How do I measure rake?

[CaptStash]

I am thinking about looking switching to a threadless fork on my ongoing re-build. The bike presently has a threaded aluminum fork. How do I go about determining the rake I need, and how much does it matter? It seems like it ought to be pretty important, but what do I know?

Saul

[dave thompson]

Pilfered from I-forget-where....

"Trail" is the blue patch along the ground in this diagram.
What it "is" is the distance away from the tire patch on the ground
that the steering axis is pointed at. The further away the steering axis
is pointed, the slower the bike steers (or more stable it feels, if you prefer)
The closer the steering axis is to the contact patch, the more nimble
the front end feels.

Generally speaking, trail falls between 5 and 6 cm's
Somewhat counter-intuitive, but more fork rake produces less trail.
More rake moves the red line forward, toward the black line of the steering
axis, thus reducing trail.

[Steve in SLO]

To re-pilfer Dave's pic, measure the rake by measuring the distance between the black line (along the center axis of the steerer) and the top of the red line (at the center of the axle) in mm. Do this measurement perpendicular to the black line. That is your rake. Usually it is between 40 and 45mm.

[akelman]

Just because someone reading this might be as stupid as I am, let me add that I think that it's actually more accurate to say that all other variables being equal, more fork rake produces less less trail. I say that because cross bikes typically have forks featuring more rake (45 or even 47) than race bikes do (a rake of 43 seems to be the norm on a race bike, right?), but I can't believe they have less trail (meaning more jittery steering) than race bikes do. Unless I'm wrong, of course. In which case, it wouldn't be the first time.

[vqdriver]

counterintuitive indeed. i tried to figure this out myself and just couldn't wrap my head around the fact that building a straight fork (inline with the ht) would increase stability.

obviously there's more at work here, and i leave that to the bike geniuses. :)

[Louis]

I may be wrong, but I think Dave Kirk once posted an ingenious way to measure rake on the fork. Later when I have time I may look for it.

[CaptStash]

Thanks guys. I'll measure the Sakai fork and see what I get. There's an Ouzo Pro with 50mm rake on eBay but I suspect that's too much rake for this bike. If anything, I wouldn't mind a little less than what I have now, the bike is a bit pokey cornering.

Saul

[akelman]

JimCav has several Ouzo Pros for sale on the forum right now. You might want to take a look at those.

[Peter B]

Excerpting a post from across the hall by Dave Kirk:

* you need the fork and three chunks of wood that are the same size and something fairly flat like a counter top. Short sections of 2x4 will work just fine. The more consistent the sizes of the pieces of wood are the better the results.

* lay two of the pieces of wood close to each other on the counter. They need to be close enough to each other so the steerer of the fork can rest on them both at the same time.

* now put the fork steerer down on the two blocks with the front of the fork facing up. You now have two of the blocks of wood under the steerer and the rake is going up toward the ceiling.

* now take the 3rd piece of wood and slide it from the dropouts of the fork up toward the crown/steerer keeping the piece of wood more or less perpendicular to the fork until it contacts the backside of both blades. At this point the fork is resting on 3 pieces of wood, two under the steerer and one under both blades.

* now using a ruler measure from the center of the axle slot of the dropout down to the table. Check both sides and tweak the wood under the blades until it reads the same on both sides. It's crucial that the steerer is still sitting on both chunks of wood.

* lastly measure the thickness of the wood under the steerer and add to that 1/2 the diameter of the steerer. This is the fork steerer centerline to the table distance. Subtract this number from the distance measured from the center of the axle slot to the counter and viola you have the actual rake. Repeat the set up a few times until you are getting consistent results to be sure and it's a done deal.

[CaptStash]

Just took a quick shot at measuring as described above and got 51mm, which seems reasonable based on the bike's "pokey" handling. I'll double check more carefully tomorrow. Now the question is, do I go with a 50mm rake fork, or risk it and try a 45?

Saul

[dave thompson]

Saul, I'd be careful selecting a new fork until you *know* the rake and *know* the trail, along with the fork 'span'. Span is the distance from the top of the fork crown (where the lower cup of the headset is installed) to where the axle on the front wheel attaches. The span of forks can be greatly different and will affect the geometry of the front end all by itself. Once you know those three criteria then you can make an informed decision about what fork to get.

Also more rake will equal 'quicker' handling and less rake will mean slower handling, so if you replaced your "51" rake fork with a duplicate that had a "45" rake, your handling would be slower. There's more to quick/slow handling than just fork rake and trail.

[shiftyfixedgear]

Too much trouble and confusion on this thread.

Don't make it harder than this needs to be - buy a new frame with a matching fork and be done with it. :)

P.S. - I don't think Sakae made a 51mm rake fork. IIRC the aluminum "Prism" road ones were available in 40 or 45mm.

[rice rocket]

Saul, I'd be careful selecting a new fork until you *know* the rake and *know* the trail, along with the fork 'span'. Span is the distance from the top of the fork crown (where the lower cup of the headset is installed) to where the axle on the front wheel attaches. The span of forks can be greatly different and will affect the geometry of the front end all by itself. Once you know those three criteria then you can make an informed decision about what fork to get.

Also more rake will equal 'quicker' handling and less rake will mean slower handling, so if you replaced your "51" rake fork with a duplicate that had a "45" rake, your handling would be slower. There's more to quick/slow handling than just fork rake and trail.

I've always heard that measurement expressed as axle-to-crown measurement.

And you have it flipped...more rake = slower, less rake = faster.

More rake moves the contact patch closer to the steer axis, reducing your mechanical trail which results in less "self centering", if you will.

[PacNW2Ford]

And you have it flipped...more rake = slower, less rake = faster.



Uhhhh...don't think so.

[rcnute]

Uhhhh...don't think so.

I'm no expert, but yeah, more fork rake/offset usually means less trail which means a quicker handling front end.

Ryan

[Peter B]

Most road bikes will vary from the mid 50s to low 60s for trail.
For a given bike, more trail (less rake) will result in stabler/slower handling at speed.
Less trail (more rake) will quicken the handling of the same bike at speed.
See the pic posted earlier.

As mentioned, a longer A-C length will effectively slacken the headtube angle and conversely a shorter fork will steepen the HTA.

[dave thompson]

I've always heard that measurement expressed as axle-to-crown measurement.

And you have it flipped...more rake = slower, less rake = faster.

More rake moves the contact patch closer to the steer axis, reducing your mechanical trail which results in less "self centering", if you will.
Span=axle-to-crown measurement; different terms for the same thing.

The closer the contact patch to the steering axis, the less 'self centering' the steering will be, i.e. quicker.

[David Kirk]

Just because someone reading this might be as stupid as I am, let me add that I think that it's actually more accurate to say that all other variables being equal, more fork rake produces less less trail. I say that because cross bikes typically have forks featuring more rake (45 or even 47) than race bikes do (a rake of 43 seems to be the norm on a race bike, right?), but I can't believe they have less trail (meaning more jittery steering) than race bikes do. Unless I'm wrong, of course. In which case, it wouldn't be the first time.

There are a few good reasons that most cross bikes have less trail than their road counterparts.

The first is the most obvious. The amount of trail desired is based on lots of stuff and one of the most important deals is how fast the bike will be ridden. Bikes with lots of trail work very well when going fast but become a real handful at lower speeds. They feel too stable and ironically 'floppy'. It's hard to get them to turn at lower speeds but at 50 mph they are great................ On the other hand bikes with low trail feel great at lower speeds - they are intuitive and precise and are easy to place exactly where you want them to be. However when speeds get higher they can become difficult to control and they get twitchy and want to wander.

So - because a cross bike is ridden at pretty low speeds most of the time a good designer will give the cross race bike less trail.

The other reason you will see cross bikes with less trail is due to the fact that the bikes are often ridden in the dirt and not on the dirt. This means that the contact patch of the tire is very long and can reach pretty far forward as the tire runs through the mud. This of course affects the functional trail and at the same time makes the bike more likely to 'crab'. We've all had a bike crab at low speeds - it's when the tire hits a bump or runs up a sidehill/camber and suddenly turns all the way to one side tossing us over the bars or causing us to highside. Running less trail makes it so the tire in the mud has a shorter lever in which to try to twist the bars out of our hands and make the bike crab. In other words we have an easier time holding out line in the deep stuff.

It's pretty late - I hope this makes sense to someone other than me.

Later and Happy Holidays,

Dave

[David Kirk]

Span=axle-to-crown measurement; different terms for the same thing.

The closer the contact patch to the steering axis, the less 'self centering' the steering will be, i.e. quicker.


Actually - span and axle-crown are a bit different and the important number here is span.

Axle to crown is simple - lay a ruler up there and measure it. The issue is that it does not factor in rake. If the fork has a large rake you will be measuring on a diagonal and not get a true idea of how the frame will sit on that fork.

Span is a bit different. Imagine looking at the fork from the side and seeing a line drawn down the imaginary centerline of the steerer. Extend this line down past the dropouts. Now make a line that is perpendicular to the first steerer line and have it go through the axle center - making an L shape if you will. Now if you are still with me here - measure from the crown race down the steerer line to the line that goes through the axle. This distance is span and is by far the most accurate way to figure in fork length.

The difference between span and axle/crown will depend on the fork's rake but it's usually in the 3-4 mm range. So to compare apples to apples one should always use the span number. The trouble is many builders and even big companies have no idea what span is and why they should even care so it can be tough to figure out.

Span is real. (I'm not sure that this will catch on as a saying)

Dave

[rice rocket]

The closer the contact patch to the steering axis, the less 'self centering' the steering will be, i.e. quicker.
Hmm, perhaps we're defining quicker differently.

Less self centering = slower steering in my view. It means the steering will tend to wander, which gives it a slow feel because it doesn't snap back to center as quickly.

I get what you're saying though...less force will be needed to steer...

[dave thompson]

Actually - span and axle-crown are a bit different and the important number here is span.

Axle to crown is simple - lay a ruler up there and measure it. The issue is that it does not factor in rake. If the fork has a large rake you will be measuring on a diagonal and not get a true idea of how the frame will sit on that fork.

Span is a bit different. Imagine looking at the fork from the side and seeing a line drawn down the imaginary centerline of the steerer. Extend this line down past the dropouts. Now make a line that is perpendicular to the first steerer line and have it go through the axle center - making an L shape if you will. Now if you are still with me here - measure from the crown race down the steerer line to the line that goes through the axle. This distance is span and is by far the most accurate way to figure in fork length.

The difference between span and axle/crown will depend on the fork's rake but it's usually in the 3-4 mm range. So to compare apples to apples one should always use the span number. The trouble is many builders and even big companies have no idea what span is and why they should even care so it can be tough to figure out.

Span is real. (I'm not sure that this will catch on as a saying)

Dave
Thanks Dave. I've always used span and axle-to-crown as interchangeable terms but as you can tell, I'm no framebuilder. That's why you make the big bucks!

[rice rocket]

Actually - span and axle-crown are a bit different and the important number here is span.

So basically span is the vertical distance while axle-to-crown is the hypotenuse if you were to form a triangle (rake being the 3rd side of it)?

Good to know. I can see why span is easily forgotten though; forks have sort of settled to 43mm on road frames, and it's a lot harder to measure to a virtual point than it is to the axle.

[Dave]

I've always heard that measurement expressed as axle-to-crown measurement.

And you have it flipped...more rake = slower, less rake = faster.

More rake moves the contact patch closer to the steer axis, reducing your mechanical trail which results in less "self centering", if you will.

While more rake does reduce trail, a smaller amount of trail makes the steering faster or more twitchy. Race bikes will have the smallest trail numbers and touring bikes the largest. A large trail makes for slow steering. The large trail does make the bike have a greater tendency to stay pointed in a straight line, so it takes more effort to make it turn. If you're decending a mountain and turning a hairpin at high speed, you have to push on the right side of the bars a little harder to keep the bike turning to the right and it will return to a straight ahead line if you don't maintain some countersteering pressure.

The formula for trail is R/tanH -(rake/sinH), where R is the tires radius and H is the head tube angle.

You'll get more trail and slower steering with larger diameter tires, a numerically smaller (slack) HTA or less fork rake.

You get the most trail with no fork rake at all. From the formula, you can see that all rake reduces trail.

Fork length is properly measured parallel to the steering tube and that is not real easy to do. Differences in the fork length will affect the HTA and steering trail. A 9mm change in the fork length will change the HTA by about .5 degree.

[David Kirk]

A picture is worth 100 words.

Dave

[Mark McM]

There are a few good reasons that most cross bikes have less trail than their road counterparts.

The first is the most obvious. The amount of trail desired is based on lots of stuff and one of the most important deals is how fast the bike will be ridden. Bikes with lots of trail work very well when going fast but become a real handful at lower speeds. They feel too stable and ironically 'floppy'. It's hard to get them to turn at lower speeds but at 50 mph they are great................ On the other hand bikes with low trail feel great at lower speeds - they are intuitive and precise and are easy to place exactly where you want them to be. However when speeds get higher they can become difficult to control and they get twitchy and want to wander.

So - because a cross bike is ridden at pretty low speeds most of the time a good designer will give the cross race bike less trail.

The other reason you will see cross bikes with less trail is due to the fact that the bikes are often ridden in the dirt and not on the dirt. This means that the contact patch of the tire is very long and can reach pretty far forward as the tire runs through the mud. This of course affects the functional trail and at the same time makes the bike more likely to 'crab'. We've all had a bike crab at low speeds - it's when the tire hits a bump or runs up a sidehill/camber and suddenly turns all the way to one side tossing us over the bars or causing us to highside. Running less trail makes it so the tire in the mud has a shorter lever in which to try to twist the bars out of our hands and make the bike crab. In other words we have an easier time holding out line in the deep stuff.

It's pretty late - I hope this makes sense to someone other than me.

Later and Happy Holidays,

Dave

Actually, I think you'll find that 'cross bikes typically have more trail, not less, than road bikes. While 'cross forks may have more offset, the head angle is generally about 2 degrees shallower on 'cross bikes than on road bikes (typically 71-72 degrees for 'cross, vs. 73-74 for road), resulting in more trail.

While what you say about flop being a problem at low speeds with a large trail is true, typical 'cross speeds are above the speeds where flop is an issue. MTBs are often ridden at slower speeds than 'cross bikes, but they typically have even more trail than 'cross bikes.

The need for steering stability (trail) is related not just to speed, but also to terrain. Extra stability (trail) is generally desired on rough and irregular terrain (i.e. off road), so MTBs and typically have a lot of trail despite their slower speeds. The amount of trail on 'cross bikes is typically between that found on MTB and road bikes, which is reflection of terrain these bikes are intended for (i.e., not as smooth as paved roads, but not as rugged as many off-road trails).

[vqdriver]

A picture is worth 100 words.

Dave

i like that even in your illustration, the fork is lugged. :)

[Mark McM]

counterintuitive indeed. i tried to figure this out myself and just couldn't wrap my head around the fact that building a straight fork (inline with the ht) would increase stability.

obviously there's more at work here, and i leave that to the bike geniuses. :)

The thing to keep in mind here is that the primary design feature that creates steering trail is the head angle. The contact patch of the wheel is directly below the fork tips (axle); but because the fork is angled forward from the head tube, the steering axis intersects the ground ahead of the fork tips (and therefore ahead of the wheel/ground contact point), resulting in there being steering trail. In other words, the wheel contact point trails the steering axis due to the forward angle of the fork. (On most wheeled vehicles this is called the castor).

If the forks legs were simply straight inline with the steerer tube, than the head angles commonly used in bicycles would result in very large trails and sluggish steering behaviour. So, most forks have a forward offset (often incorrectly refered to as "rake"*). This offset moves the wheel (and its ground contact patch) forward, without changing the location of the steering axis, thus reducing trail.

*The actual definition of "rake" is an incline from the perpendicular, for example if a ship has an angled bow, it is referred to as a "raked" bow. So technically, the head angle is the actual "rake" of the steering geometry. The distance from the steering axis to the fork tips therefore the fork's "offset" (not its "rake").

[Mark McM]

Actually - span and axle-crown are a bit different and the important number here is span.

Axle to crown is simple - lay a ruler up there and measure it. The issue is that it does not factor in rake. If the fork has a large rake you will be measuring on a diagonal and not get a true idea of how the frame will sit on that fork.

This is somewhat similar to the situation in describing the frame dimension between the head tube and seat tube. When the standard was a horizontal top tube, we simply called this the "top tube length". Now that many (most?) frames have sloping top tubes, the actual top tube length can be misleading regarding the actual size of the frame. Hence, adoption of the "effective top tube length" (the length of an imaginary horizontal top tube). So maybe the span could also be referred to as the "effective axle to crown length".

[David Kirk]

Actually, I think you'll find that 'cross bikes typically have more trail, not less, than road bikes. While 'cross forks may have more offset, the head angle is generally about 2 degrees shallower on 'cross bikes than on road bikes (typically 71-72 degrees for 'cross, vs. 73-74 for road), resulting in more trail.

While what you say about flop being a problem at low speeds with a large trail is true, typical 'cross speeds are above the speeds where flop is an issue. MTBs are often ridden at slower speeds than 'cross bikes, but they typically have even more trail than 'cross bikes.

The need for steering stability (trail) is related not just to speed, but also to terrain. Extra stability (trail) is generally desired on rough and irregular terrain (i.e. off road), so MTBs and typically have a lot of trail despite their slower speeds. The amount of trail on 'cross bikes is typically between that found on MTB and road bikes, which is reflection of terrain these bikes are intended for (i.e., not as smooth as paved roads, but not as rugged as many off-road trails).

With all due respect I don't think I'll find that cross bikes have more trail than road bikes might have. I suppose there are builders/companies that build bikes with 74° head angles which would give very little trail but I can't think of any high end bikes that are that way. I find that most high end handbuilts will have more trail on a road bike than they will a cross bike but bikes can be made in lots of ways. But when designing a bike for real cross use I find it benefits greatly from trail numbers in the 55 mm range whereas my typical road race bike will have 57 mm of trail

I think that while average speeds during a cross race are high enough to not have wheel flop be a real issue on the whole, they almost always have a section or two with very tight slow turns or bumpy/slippery off camber sections that can make a bike want to crab.

I think you'll find that when designing a bike to be used on rough terrain around a skinny tire, like spring classics bikes, that they will often run reduced trail. The reduced trail helps reduce the effects of bump steer and the additional fork rake used to give this reduced trail helps make the bikes ride smoother. This is traditional on Paris Roubaix bikes used on cobbles. Adding trail to a rough road bike makes it more difficult to control when getting bounced around as the effective lever is longer and that makes it more difficult to hold the bars steady.

Getting the trail right is just one aspect of good design but it's a vital one and if it's out of the proper range the bike can be good, but never great.

Merry Christmas.

Dave

[Mark McM]

The large trail does make the bike have a greater tendency to stay pointed in a straight line, so it takes more effort to make it turn. If you're decending a mountain and turning a hairpin at high speed, you have to push on the right side of the bars a little harder to keep the bike turning to the right and it will return to a straight ahead line if you don't maintain some countersteering pressure.

This is incorrect. Trail does not increase the tendency to stay pointed in a straight line, it increases the tendency of the front wheel to turn in the direction of lean. A straight line is simply the specific case of there being no lean.

But this also means that trail does not increase the steering force required to keep the bike turning. After the bike has been leaned over into the turn, the trail can keep the front wheel steered into the turn all by itself, whereas if there was no trail, force would be needed to keep the front wheel turned.

A bike with a large trail is easier to ride no-handed, especially when doing a turn with no hands, because the trail causes the front wheel to keep steering into the lean. A bike with less trail is more difficult to turn no-handed, because its front wheel tends to wander even when the bike is leaned into the turn.

[David Kirk]

This is incorrect. Trail does not increase the tendency to stay pointed in a straight line, it increases the tendency of the front wheel to turn in the direction of lean. A straight line is simply the specific case of there being no lean.

But this also means that trail does not increase the steering force required to keep the bike turning. After the bike has been leaned over into the turn, the trail can keep the front wheel steered into the turn all by itself, whereas if there was no trail, force would be needed to keep the front wheel turned.

A bike with a large trail is easier to ride no-handed, especially when doing a turn with no hands, because the trail causes the front wheel to keep steering into the lean. A bike with less trail is more difficult to turn no-handed, because its front wheel tends to wander even when the bike is leaned into the turn.

I think you and I see this differently.

Trail is the thing that makes the front resistant to change. So it makes it more likely to want to go straight and once you start the turn more likely to stay in the turn. I agree - once in the turn more trail makes it easier to keep in the turn and harder to get back out.

Dave

[Mark McM]

With all due respect I don't think I'll find that cross bikes have more trail than road bikes might have. I suppose there are builders/companies that build bikes with 74° head angles which would give very little trail but I can't think of any high end bikes that are that way. I find that most high end handbuilts will have more trail on a road bike than they will a cross bike but bikes can be made in lots of ways. But when designing a bike for real cross use I find it benefits greatly from trail numbers in the 55 mm range whereas my typical road race bike will have 57 mm of trail

Clearly, different designers have different preferences. But if you look at typical production bikes (Trek, Specialized, Redline Cannondale, etc.), you'll see that typically 'cross bikes have trail dimensions in the 60 - 70 mm range. For example, the Gary Fisher Cronus CX (http://www.trekbikes.com/us/en/bikes/road/fisher_cyclocross/cronuscx/) has a trail of 68 mm (for all sizes), the Specialized Tri-Cross Comp (http://www.specialized.com/us/en/bc/SBCProduct.jsp?spid=52719&scid=1001&scname=Road) has trails ranging from 75 mm for the 46 cm size to 57 mm for the 61 mm size (the 56 cm model has a trail of 63 mm), and the Redline Conquest (http://www.redlinebicycles.com/bikes/cyclocross/2011-conquest-pro) has trail that varies from 70 mm for the 44 cm size to 57 mm for the 60 cm size. The Cannondale SuperX (http://www.cannondale.com/usa/usaeng/Products/Bikes/Road/Cyclocross/SuperX/Details/2638-1XC0044GRN-SUPERX-SRAM-RED) goes even further, with trail dimension ranging from 85 mm for the 44 cm size to 64 mm for the 58 cm size. I think you'll find most other manufacturers falling in line with these geometries.

(Of course others have their own preferences for road bike geometries as well. I personally prefer my road bikes to have a trail of about 50 mm or so.)

[Mark McM]

I think you and I see this differently.

Trail is the thing that makes the front resistant to change. So it makes it more likely to want to go straight and once you start the turn more likely to stay in the turn. I agree - once in the turn more trail makes it easier to keep in the turn and harder to get back out.

Dave

I don't think we're seeing this that differently at all. Trail acts to maintain the equalibrium (balance) of lateral forces on the bike. But balance does not necessarily mean upright and going straight - you can be well balanced while leaned deeply into a hard turn. "Quickness" of a bike usually refers to how quickly you can change direction, and increasing trail decreases "quickness" - but it doesn't limit how hard you can corner once you have the bike leaned over.

What I'm getting at is that there is a perception that a very stable bike with large trail only works well when you want to go in a straight line, and can't be cornered very sharply, but that is not true at all. While it may take a stronger nudge to get a high trail bike into a turn, once you've got it leaned over it will corner just as sharply (or even more sharply) than a low trail bike. And once the bike is leaned over and balanced in a corner, a high trail doesn't cause the rider to need to use extra force on the handlebar to keep it in the corner.

[JLP]

Ok, and I apologize for thread drift in advance, but why then do some randonneurs prefer low trail for riding with a bit of weight in the bars? I can see how the longer wheelbase makes sense. I would guess the longer rake might lend some more bump absorption, but why can you ride no hands better on a bike that should be "quicker?"

Is it because we are not typically moving all that fast?

Seriously, this seems backward to me.

Dave?

[Dave]

This is incorrect. Trail does not increase the tendency to stay pointed in a straight line, it increases the tendency of the front wheel to turn in the direction of lean. A straight line is simply the specific case of there being no lean.

But this also means that trail does not increase the steering force required to keep the bike turning. After the bike has been leaned over into the turn, the trail can keep the front wheel steered into the turn all by itself, whereas if there was no trail, force would be needed to keep the front wheel turned.

A bike with a large trail is easier to ride no-handed, especially when doing a turn with no hands, because the trail causes the front wheel to keep steering into the lean. A bike with less trail is more difficult to turn no-handed, because its front wheel tends to wander even when the bike is leaned into the turn.

I'm giving you my impression of riding a bike with a lot of trail (54cm Colnago) down mountain descents with hairpin turns. It seemed to me that it required more countersteering force to keep that bike leaned into a hairpin turn, than my other bike with a much smaller trail. I've ridden over 7,000 miles of mountain descents since 2003, so I'm really familiar with high speed hairpin turns.

I strongly disagree with the idea that a bike will keep turning by itself due to having trail. Anyone who has motorcycle riding experience knows that a motorcycle (or bicycle) will not keep turning or leaning by itself without the constant application of some countersteering force. This fact is not as evident with a bicycle, since the force required is small.

It requires far more force to keep a motorcycle turning than a bicycle, but the principle is the same. The first thing I learned in a motorcyle training course was to push on the right side of the bars to lean the bike to the right and turn to the right. If you quit pushing on the bars, the bike will straighten up immediately. One of the most common causes of motorcycle accidents is failing to maintain countersteering force in a turn. When making a right hand turn and swinging too wide, some people panic and quit pushing on the bars instead of pushing harder to reduce the turning radius. The result is the bike straightens up and goes across the centerline. A bicycle works in exactly the same manner. With that knowledge, I found that my high speed cornering improved, since I knew exactly what to do if my turning radius needed correction.

[David Kirk]

Ok, and I apologize for thread drift in advance, but why then do some randonneurs prefer low trail for riding with a bit of weight in the bars? I can see how the longer wheelbase makes sense. I would guess the longer rake might lend some more bump absorption, but why can you ride no hands better on a bike that should be "quicker?"

Is it because we are not typically moving all that fast?

Seriously, this seems backward to me.

Dave?

The self centering effect on a bike is caused by a combination of many things but trail and the amount of weight on the front wheel are two of the biggies. If the rando bike has a bar bag on it and it's carrying weight then that puts that much more weight on the front wheel which makes it self center more. So less trail is needed when using a loaded bar bag. So you will see many rando bikes using pretty low trail.

Time to get to work here.

dave

[John M]

Clearly, different designers have different preferences. But if you look at typical production bikes (Trek, Specialized, Redline Cannondale, etc.), ......

I think one of the biggest differences you will see between production bikes and those built custom by someone like David Kirk is that the production bikes often use the same fork on all frame sizes. Trail (and other parameters) then are a result of the fork design, rather than the fork being designed as part of the overall frame design. Custom builders that use steel forks can make the fork to fit the desired trail, rather than the other way around.

Just because the major manufacturers do it one way does not mean that is the best way to design a bike, but usually that it is most financially viable approach for mass production.

[happycampyer]

I think one of the biggest differences you will see between production bikes and those built custom by someone like David Kirk is that the production bikes often use the same fork on all frame sizes. Trail (and other parameters) then are a result of the fork design, rather than the fork being designed as part of the overall frame design. Custom builders that use steel forks can make the fork to fit the desired trail, rather than the other way around.

Just because the major manufacturers do it one way does not mean that is the best way to design a bike, but usually that it is most financially viable approach for mass production.

Exactly. Those production geos are a mess. 85mm of trail?

Here is an expanded explanation of John M's comment:

"As stated above a bike that handles well does so due to the fact that it fits well and has the rider's weight placed well over the wheels. This is a pretty simple thing when you think about it. There is one common road block to this though. Pre-built forks with a stock rake. Most of the time these are made of carbon but not necessarily. The issue with these forks isn't that they are constructed of carbon but that the rake of the fork wasn't designed to complement the frame. If you are lucky and ride a 56cm frame then it might work out fine for you. If you don't then you can end up with a bike that fits well but handles poorly.

"There are two big things affected by fork rake. Front center (the distance from the bottom bracket center to the front axle) and trail (a measurement resulting from the combination of head angle, wheel diameter and fork rake). Front center and trail are the main contributors to a frame's handling. So why is it then that when you look at a spread sheet of Brand X's frame and fork geometry that all the fork rakes are the same, regardless of the frame's head angle? The head angles will vary from 70° to 74° but the fork rake is always 43 mm. The trail on these bikes will range from 7.8 cm (very long – will result in very slow handling and low speed instability) to 5.3 cm (pretty darn short – will result in twitchy handling and high speed instability). The way to cure this is to match the fork rake to the head angle to give the proper trail. I like to build with a trail of about 5.9-6.0 cm for the best handling. You might ask why Brand X doesn't do the same. It's really pretty simple. With the advent of carbon forks with threadless steerers they feel that they have a one size fits all situation. So unless you happen to need the middle of the road frame size with the right head angle to work with the stock fork, you may end up with a bike that doesn't handle nearly as well as it should.

"I feel strongly that the fork should be designed and built to match the frame's geometry and not the other way around. Somewhere along the line many have stopped thinking of forks as an integral part of the frameset package and more of a component like a seat post or water bottle cage. I design and build framesets where the fork rake will be what it needs to be to give the proper handling. If it needs 44 mm of rake then that's what it gets. If it needs 55 mm of rake….well you get the idea."

http://www.kirkframeworks.com/Fitting.htm

[Mark McM]

I strongly disagree with the idea that a bike will keep turning by itself due to having trail. Anyone who has motorcycle riding experience knows that a motorcycle (or bicycle) will not keep turning or leaning by itself without the constant application of some countersteering force. This fact is not as evident with a bicycle, since the force required is small.

That a bike can keep turning by itself due to trail is easily demonstrated. A bicyclist riding no-handed can ride in circles all day without touching the handlebars, so the only steering force is provided by the trail. The limit to how sharply a rider can turn no-handed is generally stability/balance while leaned over, not the amount of steering force available from trail.

It requires far more force to keep a motorcycle turning than a bicycle, but the principle is the same. The first thing I learned in a motorcyle training course was to push on the right side of the bars to lean the bike to the right and turn to the right. If you quit pushing on the bars, the bike will straighten up immediately.

All single track vehicles (like bicycles and motorcycles) require counter-steering to initiate a turn. But how much steering force is required to maintain a turn depends on many factors, including steering geometry and weight distribution. Here is a web page with more information on motorcycle steering (http://www.tonyfoale.com/Articles/Balance/BALANCE.htm). Here is the portion on the influence of trail on steering, where I have added bolding to pertinent sentences:

"STEERING EFFECT:

If we lean a stationary machine to one side and then turn the handlebars, we find that the steering head rises and falls depending on the position of the steering. In motion, the effective weight of the bike and rider supported by the steering head, is reacted to the ground through the tyre contact patch. This force tends to turn the steering to the position where the steering head is lowest (i.e. the position of minimum potential energy). For a given amount of trail, this steering angle is affected by rake angle and wheel diameter, one reason why different size wheels feel different, if all else remains the same. As long as we have positive trail, as is normal, then this turning effect is into the corner. Thus the amount of front wheel trail affects the amount of steering torque that the rider must apply (hence the feel of the steering) to maintain the correct steering angle consistant with the radius of the turn and the bike's speed. Some bikes seem to need to be held down into a corner, whilst others need the opposite approach."

So, not only does the trail generate a force to keep the wheel steered into a turn, but depending on other variables, the rider must either add or subract from this steering force (i.e. sometimes the rider must apply a counter-steering force, but other times the rider must add a steering force)

There is also some good information in the Wikipedia artiWikipedia article on Countersteering (http://en.wikipedia.org/wiki/Countersteering).

On bicycles we are fortunate that the mass of the bicycle is so much less than our body (and that the wheels have little gyroscopic progression and only small tire contact patches), so for most common front end geometries and weight distributions it is easy to lean the bike enough so that the trail provides all the steering force necessary to maintain a turn (as we demonstrate when riding no-handed).

Another interesting thing is that there seems to be a conflict in cornering advice given. Some riders claim that you have counter-steer continuously through the corner (push forward on the inside hand). This implies that the bike's natural tendency is to want steer too sharply into the corner. But you are saying that you have keep a constant steering force on the handlebars (pushing forward on the outside hand), because otherwise the bike wants to straighten out. Which advice is correct? My personal advice is for the rider to adjust their lateral weight distribution (i.e. shift their weight right or left) so that no additional force is needed on the handlebars to maintain a turn radius (i.e. let the trail do the work for you).

[Mark McM]

I think one of the biggest differences you will see between production bikes and those built custom by someone like David Kirk is that the production bikes often use the same fork on all frame sizes. Trail (and other parameters) then are a result of the fork design, rather than the fork being designed as part of the overall frame design. Custom builders that use steel forks can make the fork to fit the desired trail, rather than the other way around.

Just because the major manufacturers do it one way does not mean that is the best way to design a bike, but usually that it is most financially viable approach for mass production.

This argument may explain why production bikes may have different trails across a range of sizes, but it doesn't explain why 'cross bikes have more trail than road bikes.

Remember, 'cross bikes don't use forks off of some other type of bike. They use specialized 'cross forks. 'Cross forks are different from road forks, because they: 1) are taller and wider (to fit a larger tire); 2) have cantilever brake mounts; and have larger offsets (typical 'cross fork offset is 45-50 mm, whereas as road forks are typically 40-45 mm, and MTB forks are more typically 30-35 mm). While 'cross bikes (and their forks) may look similar to road bikes (and forks), 'cross bike forks are designed and built completely separate from road forks.

We all know that production road forks usually come in a single offset, typically about 43 mm. That number was chosen because it fits right into the middle of the range of commonly used road fork dimensions, and while not ideal in all situations, it is generally in the ballpark.

Likewise, production 'cross forks were designed to fit into the middle of the commonly used 'cross fork dimensions. And likewise, using a production 'cross fork will put the bike right into the ballpark of commonly used 'cross bike geometries - which just so happen to have trails in the range of 60-70 mm, which is more than typically found on road bikes.

Further evidence of production 'cross forks being tailored for typical 'cross bike geometries can be found by looking at their offsets. Typical 'cross fork offset is about 50 mm, which is actually longer than found on most other bikes. Offset reduces trail, so if anything, you'd expect these large offset 'cross forks to produce less trail than road bikes, not more - but instead, the 'cross forks are designed to work with common 'cross bike geometries, which feature shallower head angles, and thus larger trail, than road bikes. (The shallower head on 'cross bikes is also used to produce a larger front center and so is part of the entire 'cross bike geometry package.) The extra offset in the 'cross fork was put there to keep the 'cross bike trail from getting too large, and not the other way around.

Also, careful with the idea that the fork dimensions are the major factor in creating steering trail. Fork offset can not create trail (well, not unless you have a reverse offset fork), but instead acts to reduce trail. As I mentioned in an earlier post, it is the head tube angle that is responsible for creating trail, and is also the biggest variable in adjusting trail - For typical 700c wheel front end geometries, each degree change in head tube angle changes trail by 6 mm. Changing the fork offset is generally used to fine-tune the trail, rather than as the main variable.

I took a quick look at a number of other 'cross bike manufacturers (Ridley, Bianchi, Kona, KHS), and they all used front end geometries with 60-70 mm of trail, so this really does seem to be industry norm. Do we know of anyone other than Dave Kirk who uses smaller trails on their 'cross bikes than their road bikes?

[Dave]

Mark,

The example of a bike being ridden at a slow speed with no hands has absolutely nothing to do with a bike being ridden at speeds in the 15-50 mph range.

At very slow speeds, the bars are turned to the right in order to turn right. At high speeds, a countersteering force is required to initiate a turn and keep the bike turning. If there is no countersteering force applied, the bike will not keep leaning. In other words, you turn the wheel to the left to make the bike lean to the right and turn right.

I can tell when I'm discussing this subject with someone who has little or no experience with high speed cornering or riding a motorcycle.

You can always find an article written by an ignorant person to support an incorrect assumption, but that does not make that article correct. Spend a few thousand miles riding a bike or motorcycle on high speed descending corners. I've done both.

Your statement about countersteering force is totally wrong. My statements are not in contradiction. The countersteering force is not required because the bike wants to turn too sharply, it's just the opposite. A bike or motorcycle does not want to turn at all, when at high speed. If you don't apply countersteering pressure to initiate the lean and the turn, the bike will go straight. Either keep the pressure on or the bike won't keep turning. It will only turn too sharply if excessive countersteering force is applied.

[Mark McM]

Another interesting thing is that there seems to be a conflict in cornering advice given. Some riders claim that you have counter-steer continuously through the corner (push forward on the inside hand). This implies that the bike's natural tendency is to want steer too sharply into the corner. But you are saying that you have keep a constant steering force on the handlebars (pushing forward on the outside hand), because otherwise the bike wants to straighten out. Which advice is correct? My personal advice is for the rider to adjust their lateral weight distribution (i.e. shift their weight right or left) so that no additional force is needed on the handlebars to maintain a turn radius (i.e. let the trail do the work for you).

I forgot to mention a simple test you can perform to demonstrate that trail provides all the steering force necessary to maintain a turn.

Ride in a circle, and shift your body weight away from the bike as far toward the inside of the turn as you can, in an attempt to keep the bike as upright as possible (i.e. lean the bike away from the turn). You'll find that you need to keep an active steering force torquing the front wheel into the turn - if you don't forcefully steer the front wheel into the turn, it will try to go back to the straight ahead position. This shows that the inward lean of the bike is insufficient for the trail to steer the wheel as far into the turn as necessary.

Now shift your weight away from the bike as far to the outside of the turn as you can, in a attempt to keep your upper body as upright as possible (i.e. lean the bike down into the turn). You'll find that you now need to keep an active counter-steering torque on the handlebars, to keep the front wheel from steering into the turn too far. This shows that the inward lean of the bike is too much, causing the trail to create an excessive steering torque on the front wheel.

Between these two extremes is a balance point which will allow the trail to supply just the right amount of steering force to the front wheel to maintain the turn with no steering force applied to the handlebar. This balance point is not far from the plane of the frame, and standing on the outside pedal (which one typically does in a turn anyway) is generally enough to be able to hold this position on the bike with little effort.

[Dave]

You example has has nothing to do with a bike or motorcycle being ridden at high speed. Try turning a sharp hairpin at 30 mph with body English - it won't work. You either push on the bars (countersteering) to initiate the lean and the turn and maintain the proper amount of pressure or the bike will quit turning.

I didn't ride thousands of sharp high speed turns on bikes and motorcycles without learning how it really works.

[Mark McM]

Mark,

The example of a bike being ridden at a slow speed with no hands has absolutely nothing to do with a bike being ridden at speeds in the 15-50 mph range.

Please explain why. What laws of physics are different? Also, I ride no handed up to about 30 mph - is that in the necessary range of speeds?

At very slow speeds, the bars are turned to the right in order to turn right. At high speeds, a countersteering force is required to initiate a turn and keep the bike turning. If there is no countersteering force applied, the bike will not keep leaning.

No, a counter-steering force is necessary to intiate a turn, regardless of speed. At slow speeds this may not be obvious on a bicycle, but it is on a heavy motorcycle. The relative magnitudes of the forces and angles of steering and leaning may vary with speed, but the same physical laws apply.

I can tell when I'm discussing this subject with someone who has little or no experience with high speed cornering or riding a motorcycle.

You can always find an article written by an ignorant person to support an incorrect assumption, but that does not make that article correct. Spend a few thousand miles riding a bike or motorcycle on high speed descending corners. I've done both.[/QUOTE ]

It is true that I have little motorcycling experience, but I have plenty of experience cornering at high speed on a bicycle (which is what this discussion is about). Rather than falling into the logical fallacy of "appealling to authority", why don't we stick to what can be observed and confirmed?

[QUOTE=Dave]Your statement about countersteering force is totally wrong. My statements are not in contradiction. The countersteering force is not required because the bike wants to turn too sharply, it's just the opposite. A bike or motorcycle does not want to turn at all, when at high speed. If you don't apply countersteering pressure to initiate the lean and the turn, the bike will go straight. Either keep the pressure on or the bike won't keep turning. It will only turn too sharply if excessive countersteering force is applied.

I think there is no doubt that a dynamic countersteering action is required to initiate a turn. The question is, what (constant) steering torque is necessary to maintain the turn?

Clearly, after stabilizing into a constant radius turn, the steering angle will be constant. If a constant countersteering torque is necessary to maintain the turn, then it means that the wheel wants to steer into the turn (and we are countering that action with a countersteering torque). In this case, the trail (or some other mechanism) is generating a steering torque that we need to counterbalance to maintain a constant steering angle. If we don't maintain the countersteering torque on the handlebars, then yes, the net result will be to straighten out the turn, but that is because the the initial action will be a momentary steer further into the turn, which reduces the lean, which in turn requires the bike to straighten its line.

So, if you are saying that countersteering torque is necessary to maintain a constant arc turn, then that can only mean that the steering mechanism (predominantly the trail) is producing a torque to steer the front wheel into the turn. Since trail acts in response to the lean of the bicycle that further means that there must be some lean angle of the bicycle were exactly the right amount of steering torque to maintain the turn is generated. Leaning a motorcycle to this angle might be difficult, but it is easy to do on a bicycle.

[Dave]

Mark,

Your posts may be full of technical mumbo jumbo, but they are still wrong. Anyone with any significant amount of motorcycle riding experience knows that it requires a constant countersteering force to keep a motorcycle turning. They don't have to be able explain it to know what works and they know that a the bike won't reach some balance point where it keeps turning all by itself at high speed.

The same thing applies to a bicycle, only with far less countersteering force.

The fact that you posted a really dumb remark about needing to countersteer more because the bike wants to turn too sharply tells me that you are clueless. You countersteer more because you're not turning sharply enough. That's what I explained in plain English in my first post - the common cause of a motorcycle wreck. Quit pushing on the right side of the bars in a right turn and you will swing wide, go over the centerline and into on coming traffic, or off the left side. The same thing will happen with a bicycle. I've experienced this myself. When I first started riding long mountain descents with hairpin turns, I learned quickly that it was easy to drift wide and end up over the centerline. You can't just initiate a turn and expect the bike to keep turning at the proper radius on it's own.

You ask what's different about turning a bike at high speed versus low speed:


http://www.youtube.com/watch?v=VC_XNOXwQAo

[Mark McM]

I was away a few days for the holiday ..

The fact that you posted a really dumb remark about needing to countersteer more because the bike wants to turn too sharply tells me that you are clueless. You countersteer more because you're not turning sharply enough.

Wow, these statements completely dumbfound me that you can't see the logical flaw in them. Countersteering is pushing (torquing) the handlebars to steer the front wheel away from the direction of the turn. The only way that you can stay in a turn while trying to steer the front wheel away from the turn is if there is some other torque on the front wheel steering it toward the turn, counterbalancing the countersteering torque. This is the simple physical principle of action/reaction. Newton's law's of motion demand this, and there is simply no way around it (if you believe otherwise, then you are essentially denying the fundamental principles of physics).

Quit pushing on the right side of the bars in a right turn and you will swing wide, go over the centerline and into on coming traffic, or off the left side. The same thing will happen with a bicycle.

These statements just confirm the existence of a torque steering the front wheel into the turn. As you should know, in order to straighten out a turn, you first need to steer the front wheel more sharply into the turn momentarily, which acts to reduce the angle of lean, and with the smaller lean angle the turn radius will be larger (essentially similar but opposite to the countersteering that initiated the turn). If the rider doesn't turn the front wheel in themselves to widern the turn, then there must exist some other steering torque which is turning the front wheel more sharply into the turn.

It is unfortunately that you don't recognize this torque that acts to steer the front wheel into the turn, since this discussion was started about the affect of trail on cornering, and trail is the primary factor in generating this steering torque. The steering trail causes the front end geometry to respond to a lean by generating a torque to turn the front wheel into the lean (also caused the castor torque). By varying the amount of lean of the bicycle, the amount of trail steering torque is also varied, which varies the amount of countersteering that needs to be applied. In fact, the lean can be adjusted so that no countersteering torque is required to keep a bicycle turning. Here's a related tidbit: Keith Code (http://en.wikipedia.org/wiki/Keith_Code), a motorcycle racer & coach and founder of the California Superbike School (http://www.superbikeschool.com/), also co-authored a book on bicycle racing technique called A Gear Higher (http://www.amazon.com/Gear-Higher-Bicycle-Handbook-Techniques/dp/0965045005), which primarily concerned itself with bicycle cornering technique. I have read it, and not once does it mention countersteering to stay in a turn.

You ask what's different about turning a bike at high speed versus low speed:

http://www.youtube.com/watch?v=VC_XNOXwQAo

This video says nothing at all about how gyroscopic precession effects a bicycle at all, let alone why there should be a difference at different speeds. However, this book says quite a bit about gyroscopic precession (and many other variables) on both motorcycles and bicycles:

Motorcycle Handling and Chassis Design Design, the Art and Science (http://books.google.com/books?id=84hF-qoR5I8C&printsec=frontcover&dq=motorcycle+handling+and+chassis+design&source=bl&ots=FYE1tGR7Kj&sig=02mNzcQ0VB6VXxKFxSQN2LJN3w8&hl=en&ei=iCUYTfrfCYa8lQfXipHICw&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CBoQ6AEwAA#v=onepage&q&f=false)


Of particular interest here is section in chapter 4 (Balance and steering) called "Self-steering", which describes the ability of the front wheel geometry to have a self-steering affect when there is an imbalance of lateral forces, and that the direction of self-steering will depend on the direction of imbalance. Or, in other words, countersteering by the rider will be necessary if the bike is laterally imbalanced, but it is not necessarily if the bike is balanced. Or at least so says the guy that wrote the book on motorcycle chassis design.

I have no doubt that you are a good bike handler and corner well at high speed. But, there is more than one to corner on a bicycle (or a motorcycle), and there are ways to corner a bicycle without the necessity to continually apply a countersteering torque. (And remember, being able to do something is not the same as understanding how it is done.) But in the end, if you still contend that a bicycle does not have an inherent self-steering effect causing to remain steered into a turn, then you need to argue with Isaac Newton and Tony Foale (the author of the motorcycle chassis design book mentioned above).

[akelman]

you need to argue with Isaac Newton

His screen name used to be "!%?@ing Apple", but everyone assumed he was a PC guy, so he changed it to something else. He's pretty hard to reach now. Has been for a few hundred years.

[Dave]

What I recognize is someone with no real experience with the subject that he claims to understand.

The techniques that I describe work, or I would not have survived thousands of miles of high speed cornering descents on both bike and motorcycle.

You'd do well to take a motorcycle training course. The same principles apply to a bike. The only smart way to turn either one is using the simple method that I describe.

About all you have to remember is to push on the side of the bars, in the direction you want to turn and keep the inside pedal up, so it doesn't hit the ground. If the turn is too tight, let up on the pushing and the bike will straighten itself. Some people insist in weighting the pedal that's down, but it's not necessary. About all it does in increase the weight on the front a percent or two. It might yield some benefit if your setup makes the front of the bike too light. I haven't found a rider yet that I couldn't keep up with or pass on a technical descent. At some point, it becomes a contest to see who's most willing to risk a slideout, since there's really no way to judge the available traction. Hit a little patch of sand and it's all over.

[Mark McM]

What I recognize is someone with no real experience with the subject that he claims to understand.

Right back at ya!

The techniques that I describe work, or I would not have survived thousands of miles of high speed cornering descents on both bike and motorcycle.

Yes, the technique you describe has been used quite successfully by many people. But it is not the only technique that can be used successfully.

You'd do well to take a motorcycle training course.

If I were to take up motorcycling, that would probably be a good idea. However, I have participated in several bicycle handling workshops, including ones lead by John Allis (http://en.wikipedia.org/wiki/John_Allis) and Dick Ring (sometimes called the "Voice of New England Racing", Dick Ring was head coach of the North American School of Bicycle Racing, which he co-founded with Bill Farrell who you may know as the developer of the "Fit Kit" bicycle fitting system).

About all you have to remember is to push on the side of the bars, in the direction you want to turn and keep the inside pedal up, so it doesn't hit the ground. If the turn is too tight, let up on the pushing and the bike will straighten itself.

In addition to pushing forward on the inside handlebar, you are probably also pushing down on the handlebar, causing the bicycle to lean into the turn a bit more than your CG. This extra bicycle lean causes the trail to generate a caster torque which acts to steer the front wheel more sharply (and which you are opposing with your countersteering torque).

The method taught by Dick Ring was the opposite of your method. He taught that the rider should try to keep the bicycle as upright as possible, and to actively push forward on the outside handlebar to keep the bicycle steered into the direction of the turn. With this method, the bicycle is actually leaned less into the turn than the CG, which causes the trail to generate a reverse caster torque, which the rider has to oppose by torquing the handlebars into the turn. Dick Ring claimed that this method gave better tire traction, although I don't believe this claim, and I personally don't believe that this is the best way to corner.

My preferred method is instead to adjust the biycle lean angle so that the caster torque is just enough to keep the front wheel steered into the corner, eliminating the need for the rider to actively torque the handlebars. (this also keeps the rider more in plane with the bicycle, improving stability.)

So, different methods are possible to corner a bicycle, and each method uses the self-steering effect (caster torque) of the front end geometry differently, and different riders may prefer different methods. You may have noticed in motorcycle racing that some riders stay nearly centered on their bikes, while others actively hang off their bikes towards the inside of the turn - again, different methods to accomplish the same task. (The motorcycle design book referenced above talks a little about the affects of each one in regard to turn initiation rate.) If you study steering dynamics more deeply you'll see that both motorcycles and bicycles have an "inversion speed", in which the direction of the rider steering torque reverses, and this speed depends on many factors including steering geometry, gyroscopic procession and tire width and friction (more on this can be found in the book Bicycling Science (http://books.google.com/books?id=0JJo6DlF9iMC&pg=PA291&lpg=PA291&dq=motorcycle+caster+%22steering+torque%22&source=bl&ots=Tr0BEMgzj0&sig=Jd7EXNk_1yjhdwSEDcYFyX6yKJA&hl=en&ei=v2EZTfmYJoaglAe9pdDbDA&sa=X&oi=book_result&ct=result&resnum=10&sqi=2&ved=0CEsQ6AEwCQ#v=onepage&q&f=false) ) .

(And of course, regardless of which turn method used, ALL turns must be iniated, and finished, with countersteering. But whether that countersteering torque must be maintained in the middle of the turn depends on the lean method used for the turn.)

I haven't found a rider yet that I couldn't keep up with or pass on a technical descent. At some point, it becomes a contest to see who's most willing to risk a slideout, since there's really no way to judge the available traction.

Yes, I agree that the degree of confidence and/or daring of the rider is a major factor (and sometimes the biggest factor) in how fast a rider can corner/descend. (And likewise, I'm one who doesn't get left behind on a downhill. Uphills are different story ...)



And speaking of trail, I forgot to mention the other reason off-road bikes typically have larger trail: It reduces the chance of reverse trail occurring. Trail is the distance between the tire contact point and the where the steering axis intersects the ground. With normal (positive) trail the tire contact point is behind the steering axis. But if the rolling wheel hits an obstruction (rock, root, etc.), then depending on the size and shape of the obstruction the tire contact point on the obstruction can be ahead of the steering axis, resulting in a momentary reverse trail (tire contact point ahead of the steering axis). If the front wheel isn't aimed directly ahead, this reverse trail can momentarily generate a reverse caster torque, which tries to turn the front wheel in the wrong direction and causes instability. In extreme cases it can cause a "jack-knifing" effect, which, if the rider doesn't react quickly and steers against the reverse caster torque, can cause the front wheel to steer out from under the rider and dump them on the ground.

A larger trail moves the steering axis further ahead of the wheel contact point, reducing the chance of reverse trail occurring, and reducing the reverse caster torque if it does occur. X-Country MTBs typically have about 80mm of trail, and downhill MTBs will generally have more.

[Dave]

I've never seen anyone who could write so much and say so little.

For example: "My preferred method is instead to adjust the biycle lean angle so that the caster torque is just enough to keep the front wheel steered into the corner, eliminating the need for the rider to actively torque the handlebars. (this also keeps the rider more in plane with the bicycle, improving stability.)"

All that and you've told the reader nothing about how to steer the bike. What bit of magic eliminates the need to torque the handlebars? Why would my technique keep the rider less "in plane" with the bicycle? I don't deliberately lean to the side in a turn.

If you'd ever ridden a motorcycle, you'd know that this does not happen. A bike or motorcycle will straighten up and quit turning if the bars don't have some torque on them. You apply the amount of torque needed to turn at the required radius. If you're not turning sharp enough, push harder on the inside bar. This method is simple enough for anyone to understand. The problem with a bicycle is the force required is small and not always apparent to the rider.

There is no way that you could push on the outside bar and turn in the proper direction. The outside bar in a right turn is the left side. Push on the left and the like will turn left, not right, and then it's the inside bar.

Your comments about riders hanging off the side of a motorcycle also reveals how little you know about the subject. It's not a "different" way to turn a motorcycle. Those guys are still pushing on the right side of the bars to turn right. The idea is to lean the bike less at a given speed, or attain a greater speed at a given amount of lean. It's totally unnecessary for normal street riding. Only sport bikes with lots of footpeg and muffler clearance can benefit from that technique. Cruiser bikes will drag the pegs or pipes with far less lean angle.

[RPS]

IMHO you are both missing a bigger picture – dynamic and very fluid problems can’t be analyzed successfully using static reasoning; and to discuss in such terms will only lead to confusion, frustration, and ultimately insults.

While visiting family for the holidays I followed this thread with interest and curiosity as it morphed from measuring rake, to the effect of rake on trail, the effect of trail on steering, to how to ride a bicycle, to the need for the infamous coutersteering …… and to cover all bases motorcycles too. I think that covers most of it.

It’s a great topic deserving discussion but seems odd under a thread questioning how to measure fork rake – not that there is anything wrong with drifting. Bottom line it appears to me that one of you is arguing primarily based on theory and the other on practice ...... kind of the why versus the how things work. Minor distinction if both correct. ;)

[dave thompson]

RPS, thanks for saying so much to so many in so few words! :beer:

[Dave]

We can't both be right. You'll never find a discussion on motorcycle steering that mentions the point where no countersteering force is required and motorcycle just turns by itself. At any decent speed, that does not happen. You have to push harder on the bars to turn sharper - that's simple to understand and easy to prove on your first ride.

There are techniques that can be used to reduce the amount of countersteering force for a motorcycle (applying weight to the inside footpeg), but you can't do that with a bicycle. The only peg on a bicycle is the pedal and the inside pedal better be up.

[Mark McM]

I've never seen anyone who could write so much and say so little.

And likewise, you appear to read so little and ignore so much. I've provided several references to material on bicycle and motorcycle turning and stability, but it appears you have decided not to look at any of it.

For example: "My preferred method is instead to adjust the biycle lean angle so that the caster torque is just enough to keep the front wheel steered into the corner, eliminating the need for the rider to actively torque the handlebars. (this also keeps the rider more in plane with the bicycle, improving stability.)"

All that and you've told the reader nothing about how to steer the bike. What bit of magic eliminates the need to torque the handlebars?

You just quoted the answer above - it is the caster torque (from the steering trail) that can be used to eliminate the need to torque the handlebars. Why are you deliberately ignoring this effect?

Why would my technique keep the rider less "in plane" with the bicycle? I don't deliberately lean to the side in a turn.

I presumed that you leaning to generate a caster torque. You have still not said what torque you need to countersteer against.

If you'd ever ridden a motorcycle, you'd know that this does not happen. A bike or motorcycle will straighten up and quit turning if the bars don't have some torque on them. You apply the amount of torque needed to turn at the required radius. If you're not turning sharp enough, push harder on the inside bar.

I have never disagreed that pushing on the inside bar will initiate a turn, and pushing harder will sharpen the turn. Where we disagree is whether you need to keep pushing on the bar to maintain a turn. Depending on many factors (speed, steering geomtry, gyroscopic precession, tire forces) you may not have to torque the bar at all to maintain the turn, and in some cases the rider will have to actively torque the bars into the turn.

There is no way that you could push on the outside bar and turn in the proper direction.

That's not what everyone else says. For example in the published paper Motorcycle Steering Torque Decomposition (http://www.iaeng.org/publication/WCE2010/WCE2010_pp1257-1262.pdf) says that in some speed realms a positive steering torque may be required:

"Among the three tested vehicles, the decomposition analysis is detailed herein only for the touring motorcycle. Figure 5 depicts the steering torque while cornering on a right turn with speeds from 5 to 30 m/s and lateral accelerations from 0 to 6 m/s2, i.e. in a range of motion conditions which contains the tested conditions. The torque is negative, which means outward the turn, only for low speeds (lower than 10m/s) and then increases both with speed and lateral acceleration (i.e. roll angle)."

Your comments about riders hanging off the side of a motorcycle also reveals how little you know about the subject. It's not a "different" way to turn a motorcycle. Those guys are still pushing on the right side of the bars to turn right.

Yes, but those hanging off the bike countersteering less. See Steering in Bicycles and Motorcycles (http://www.utahsba.com/docs/SteerBikeAJP.pdf). This paper has some simple graphs showing required handlebar torque during a turn. Note that there is essentially no torque in the middle of the turn, the only handlebar torque is countersteering torque to start the turn and steering torque to end the turn. It also describes how, on a motorcycle, using lateral hip thrust (as in leaning off) can reduce the amount of countersteering torque to initiate a turn.

[Mark McM]

IMHO you are both missing a bigger picture – dynamic and very fluid problems can’t be analyzed successfully using static reasoning; and to discuss in such terms will only lead to confusion, frustration, and ultimately insults.

Yes, I agree that it is a dynamic situation with many variables. Also, I wasn't the one that dragged in motorcycle dynamics (I've only responded to it because there is much more material published about motorcycles than bicycles). I have only been trying to explain that caster torque (governed largely by steering trail) is sufficient to keep the front wheel of a bicycle steered into a steady state turn without the rider having to continuously push on the handlebars. Also, I have said several times that there are several techniques that can be used to corner a bicycle, which use the dynamic forces of cornering to a greater or lesser effect. It is Dave that insists that there is one (and only one) way to corner. I've been trying to refrain from insults, and instead tried to explain and add material to support my arguments

Bottom line it appears to me that one of you is arguing primarily based on theory and the other on practice ...... kind of the why versus the how things work. Minor distinction if both correct. ;)

See the quotes from motorcycle instructors in the next post to see how the theoretical meets the practcal.

[Mark McM]

We can't both be right. You'll never find a discussion on motorcycle steering that mentions the point where no countersteering force is required and motorcycle just turns by itself.

I guess this means that you are the one that is wrong. Here is a current discussion on the California Superbike School forum about countersteering (http://forums.superbikeschool.com/index.php?showtopic=2547) , in which one of the schools riding coaches (Jason Wood) says in response to a question about countersteering:

"Once the motorcycle is at speed you initiate a turn by counter steering, once the bike is leaned into the turn, you release the pressure on the bars entirely, the motorcycle will remain at that chosen lean until you tell it to do otherwise. The pressure sequence on the bars is simple: Press, then Release.

Suspension, tire pressure and wear may have an influence but for the majority, just press, then release.

There's a VERY important reason why releasing the pressure on the bars is beneficial, anyone able to chime in with reasons as to why we would want to get as relaxed on the bars as soon as possible? "

So, the superbike racing coach says that you don't need to countersteer after turn initiation. If you disagree, maybe you should join in on that discussion.

You mentioned taking a motorcycle training course. Here's some advice on cornering from the Motorcycle Education of New Jersey (http://www.rider-ed.com/stability-cornering.aspx) organization which offers coursed approvedy b the Motorcycle Safety Foundation:

"Once the bike is leaned over to give the turn radius you want, ease pressure on the bar. Motorcycle steering geometry (primarily trail again), tire profile and other factors tend to keep the bike stable in the turn. Depending on a number of factors, the motorcycle may even track through the turn with no subsequent steering input (ie it may require NO steering force in the turn to keep the bike stable through the corner)."

So there it is again in plain English from a motorcycle riding instructor - no steering force may be necessary to keep the bike in a corner. If you believe they are wrong, maybe you should contact them and alert them to their error.

Further, there are several publications on motorcycle (and bicycle) dynamics which discuss the "inversion speed", when the rider steering torque reverses, and the rider may need to apply torque into the direction of the turn. I have already mentioned this above, and referenced several sources which talk about it, but here is some more information from the book Motorcycle Dynamics (http://books.google.com/books?id=rJTQxITnkbgC&pg=PA254&lpg=PA254&dq=motorcycle+capsizing+steering&source=bl&ots=DXjQEfaPsE&sig=wDgQKIKNSo2-wvIs3DlK754KcjI&hl=en&ei=rgsaTYjVE42asAO0ts3cAg&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CBMQ6AEwAA#v=onepage&q=motorcycle%20capsizing%20steering&f=false) by Vittore Cossalter:

"4.8.1 Torque components

In Fig. 4-28 the variations of the torque applied by the rider to the handlebas of the sample motorcycle is shown. It is useful to recall that the torque exercised by the rider is, by definition positive if it tends to increase the steering angle into the turn.

This means that there are essentially two possible situations:

- at low velocities the steering torque is negative. Therefore, in steering, the rider must block the handlebars, which otherwise tend to rotate further. When the values of the steering torque become strongly negative, the inclination and the entry into the turn become easier;

- with an increase in velocity, the torque to be applied to the handlebars becomes positive. This circumstance, if the values of the torque remains high, generates in the in the rider the unpleasant sensation of driving a motorcycle that is hard to incline and insert into turns."

This is saying that in some situations, at higher speeds the rider may have to actively steer the handlebars into the turn, not countersteer.

More from this book:

"Rider Position

A forward displacement of the rider's center of mass has a slight self-steering effect. The vertical position of the rider's center of mass has a very small aligning effect. The result is that if the rider moves, always remaining in the plane of symmetry of the motorcycle, the steering behavior doesn't change significantly. On the contrary, a lateral displacement of the rider toward the inside of the curve has a strong aligning effect. Considering that sport riders usually move sideways considerably it is obvious that the steering characteristics of the motorcycle are strongly influenced by the driving stye. An expert rider can take advantage of this phenomenon and shift the zone of low steering torque to match the current steering conditions and thus gain better, easier steering control."

This again confirms that riding style influences the amount of steering torque required from the rider - just like in bicycles.

There are techniques that can be used to reduce the amount of countersteering force for a motorcycle (applying weight to the inside footpeg), but you can't do that with a bicycle. The only peg on a bicycle is the pedal and the inside pedal better be up.

Not true - shifting your upper body to one side or the other can also produce the desire weight shift (some describe this as angling the hips). Since a bicycle has much less mass than motorcycle (and much less mass than the rider as well) it is easy to induce a significant weight shift and change in lean angle of the bicycle by angling the upper body. And since the gyroscopic precession and tire shape/friction forces are much less on a bicycle than on a motorcycle, not a lot of lean is required to adjust the caster torques (from lean and trail) for the bicycle to self-steer to maintain the turn.



But, I'm probably wasting my breath here. You keep insisting that you are right, but won't provide any outside evidence to back it up. You won't address or comment on references to descriptions of the torques/forces involved in cornering and instead reply with ad hominens. Your assertions contradict published books on bicycle and motorcycle design and handling. Your cornering technique descriptions go against the advice of Motorcycle Safety Foundation instructors and the teaching of an an instructor at the California Superbike School who say that motorcycles can be self-steering in a turn. You appear to be acting like a flat-earther who dismisses any evidence that disagrees with your own viewpoint, and can not be dissuaded by any argument.

At this point all I can do is shrug my shoulders and say "whatever, dude."

[Dave]

The problem is that you can't put into simple English, what the other methods of turning are.

I say push on the right side of the bars (countersteering) to make the bike lean to the right and turn to the right. I say that the bike will return to a straight-up and straight ahead position if you quit pushing. Also push harder if the turn radius is not sharp enough or let off a bit if the turn is too sharp. The bike won't keep turning by itself.

I also say that there is no body English or special body position required to make an effective turn at high speed. Just don't forget to keep the inside pedal up. While it may be possible to turn a bike in some other manner, it's not going to enhance cornering precision or get the bike around a corner any faster.

My only evidence that this works is surviving thousands of cornering manuevers over about 7000 miles of high speed mountain descents, since I moved to Colorado in 2003. If what I describe doesn't work, I'd be dead. I have no lengthy technical argument. I just know what works and it's not complicated.

I've only ridden a motorcyle about 4000 miles. I rode a sport bike, not a cruiser, for one year, mostly in the mountains. I never experienced a self-steering condition, ever. I just followed the instructions that I got from my instructor, a veteran motorcycle cop. It seemed to work. It's the same method that I describe for turning a bicycle, except for keeping the inside pedal up. I lived through a lot of the same mountain corners that I rode with my bicycle. Never failed to stay on my side of the road.

What I find odd about some of the motorcycle countersteering discussions is no mention of how to stop the turning, if the bike is really turning by itself with NO countersteering. I never pushed on the opposite side of the bars to quit turning, I just quit countersteering and the bike quit turning all by itself. Of course, I never quit countersteering in a turn either, since my instructor never mentioned a bike turning by itself, after a turn was initiated. The idea of "easing up" on the countersteering after initiating a turn is not the same as no countersteering force at all. I always made adjustments to the countersteering force, as required to keep the bike where I wanted it, but I never felt that the bike was steering itself. I also never used my left hand to bring the bike out of a right hand turn. If I ever resume motorcycle riding, I'd certainly give that tecnhique a try, but it was not what I was taught.

http://www.rider-ed.com/stability-cornering.aspx

Just as a test, I have completed high speed right hand corners on my bicycle, using only my right hand, with an open palm, so it was not possible to pull on the bars or push on the left side to bring the bike out of a turn. All I did was push to turn and quit pushing to quit turning. I make a special effort to make my right turns only with my right hand and left turns with my left hand.

[swg]

Remember when we had stingrays? We would throw our baseball glove onto the handlebars and carry the bat on our shoulder. We could then pop a wheelie and ride for blocks and if I remember correctly it was easier to turn left with the bat on your right shoulder and right with the bat on your left shoulder. Or was it the other way around?

[vqdriver]

no joy

[PacNW2Ford]

Remember when we had stingrays? We would throw our baseball glove onto the handlebars and carry the bat on our shoulder. We could then pop a wheelie and ride for blocks and if I remember correctly it was easier to turn left with the bat on your right shoulder and right with the bat on your left shoulder. Or was it the other way around?

Not only that, you could flip the front wheel completely around and ride with a slack head tube angle and negative rake, and dream about how you would impress people with your theories on bicycle handling on the internet. 'Cept of course, no one had ever heard of the internet in 1969 and we actually rode our bikes for fun.

[swg]

Actually I have enjoyed the thread and have learned several things about rake, trail, span, etc. that I didn't know. That is what is great about this forum. I also thought about how I cornered and I think the opposing opinions have probably prompted most of us to think through how we take a corner. These gentlemen are actually so close to describing the same technique that it is quite amusing. One element that I don't remember being mentioned is acceleration at the apex of a turn which is very critical to executing a turn and impacts the balance of the bike/motorcycle and the need to keep proper pressure or lack of pressure on the handlebars. (that should get it going again) It seems to me the sharpness of the turn has much to do with how it is executed. Hairpin or sweeper? Downhill or uphill? We all do it without thinking and that is what made me think back to riding our stingrays around corners while doing a wheelie with a bat on our shoulder. Thought it would lighten things up and to remember that we indeed ride our bikes for fun. Forgot about flipping the handlebars around.

[NRRider]

So question--if a bike has a wheelbase of 99.2 cm specified for a 4.3cm rake and instead the fork being used has a 4.7cm rake, can you tell me what the difference in wheelbase will be?

[David Kirk]

The rake is pretty close to being a horizontal measurement so you can figure about 3-4 mm longer.

dave