Geometry discussion?

[tylercheung]

I had heard the phrase "Italian stage race" geometry being thrown around, and found this on Google: http://redkiteprayer.com/2016/01/anachronistic/

For frame builders and people familiar w/ geometry parameters and characteristics, how much does this ring true?

Overall, I've focused mostly on basic "will the frame fit" measurements, primarily top tube, seat tube, standover height and head tube length/amount of spacers under the stem. Some thoughts re tubing diameters, materials, etc too but just a layperson's understanding...

In terms of the other types of parameters - BB drop, trail calculations from the fork, head/seat-tube angles and chain stay length...I haven't had as much exposure, although this is where the magic of the bike handling and ride characteristics happen? would be good to get a good "geometry 101" understanding in my head to better appreciate different frames....

[unterhausen]

Late '70s American crit geometry often had 75 degree head angles and 11+ inch bb height with a 20mm tubular tire, whatever that works out to be for bbf drop. Yeah, we were silly back then.

I guess things had moderated by the time designs made it to Asian manufacturers.

[Kontact]

Merckx is known for his low trail bikes, so the article seems like bunk for that and several other reasons.

Other Italian bikes had variable trail - the same rake was and still is used on all HTAs.


I have never seen nor heard of an American bike in a common size with 75° HTA, either.

Where are these numbers coming from?

Classic American geometry (if it ever existed), as far back as the early '80s, was the whole neutral steering thing.

[Kontact]

If you scan down in the comments of the article you'll find Richard Sachs calling shenanigans on the claims about historical geometry.

[tylercheung]

Ah right, the comments...interesting to pore over those...

[Kontact]

I've been pouring through geometry charts dating back to the early '80s, and most every general claim I hear about different periods or brands seems to have little to do with reality. People talk about geometry of different bikes as if they were polar opposites, but I've had a hard time finding these super tight geometry crit bikes of the '80s or how supposed long and slow Lemonds are.

But it is hard to sell "endurance" geometry if you can't make it sound like "race" geometry is actually much different.

[FlashUNC]

Just to throw something on the woodpile. Feel free to chew this apart. The numbers for my Della Santa. The best riding bike I've ridden, and the basis for my Rock Lobster as well. 42mm fork rake, a touch more BB drop and a longer wheelbase coupled with a 74-ish degree head angle.

https://c1.staticflickr.com/9/8534/8748538077_70d94bdeb2_b.jpg

[cmg]

i always thought "Italian stage race" geometry meant a longer wheelbase for riding over imperfect roads. is there a common "gravel" road geometry? i would think they would be similar. the idea is to put more weight over the rear wheel. steer with your hips. the attachment makes some good points.

[steelbikerider]

My custom Schneider is 59/59 with 72.5/74angles, 43 mm rake, 7.5 cm BB drop and 410mm chainstays. I can ride all day on it. It is on its 4th group set and well over 50000 miles. I don't know what geometry it is but it works.

[weisan]

http://www.cyclofiend.com/Images/rbw/gen1/rivcat05_roadstandard.jpg

[Kontact]

i always thought "Italian stage race" geometry meant a longer wheelbase for riding over imperfect roads. is there a common "gravel" road geometry? i would think they would be similar. the idea is to put more weight over the rear wheel. steer with your hips. the attachment makes some good points.

I don't think anyone agrees on what a gravel or endurance bike bike is, let alone their geometry.

How does having longer chainstays put you more over the rear wheel???

[cmg]

I don't think anyone agrees on what a gravel or endurance bike bike is, let alone their geometry.

How does having longer chainstays put you more over the rear wheel???

longer chain-stays is for more stablity and it lets you slacken the STA that will put more weight on the rear.

[Kontact]

longer chain-stays is for more stablity and it lets you slacken the STA that will put more weight on the rear.

If you move the rear wheel closer to you, it will take more of your weight and the front less. If you move the rear aft, it will take less of your weight and the front takes more.

If you move both front and rear they each take the same weight they did before.

The only way to put more weight on the rear wheel and less in front is to either make front center longer or the chainstays shorter.

[Peter B]

Just to throw something on the woodpile. Feel free to chew this apart. The numbers for my Della Santa. The best riding bike I've ridden, and the basis for my Rock Lobster as well. 42mm fork rake, a touch more BB drop and a longer wheelbase coupled with a 74-ish degree head angle.

https://c1.staticflickr.com/9/8534/8748538077_70d94bdeb2_b.jpg

Della who?

But seriously, I suspect Roland has forgotten more than many new builders are likely to ever learn.

BTW, get offa my lawn!

[jerk]

the article is bogus. old italian guys understood that you needed to build the race bike around the racer...those and the size of the wheels were the two constants. what that generally meant was that small bikes had steep seat angles and shallow head angles and lots of forks rake and big bikes had slack seat angles and steep head angles without much rake. i don't think you could find an italian frame builder who knows or cares about trail....especially not prior to everything moving to asia.

listen- race bikes have certain constants geometrically you need to deal with, principle among them is the diameter of the wheels and you need to do your best to keep the wheelbase within range and the weight balance where it ought to be. the way to achieve this is to put the big guy between the wheels in the right place and and put the little guy between the wheels in the right place. there isn't an "italian" or an "american" geometry- there are just good race bikes and bad ones- and the good ones deal with the riders morphology and put the wheels in the right place....like that della santa posted above. i am also 100% sure there is no way Merckx rode anything like what is described as "italian" geometry in that article or anything like that picture. having seen many of his bikes they tended to be exactly what you'd expect for a big powerful guy who carried a lot of his weight in his shoulders....moderate to slack seat angles, steepish head angles (although not at the extreme) and regular fork rakes and bottom bracket drops for bike his size. look at a stock 59cm Merckx Century geometry and you get an idea.

[Kontact]

Just to throw something on the woodpile. Feel free to chew this apart. The numbers for my Della Santa. The best riding bike I've ridden, and the basis for my Rock Lobster as well. 42mm fork rake, a touch more BB drop and a longer wheelbase coupled with a 74-ish degree head angle.

https://c1.staticflickr.com/9/8534/8748538077_70d94bdeb2_b.jpg

What size tires was this designed for? With tires less than 38c it is low trail.

[weisan]

http://farm8.staticflickr.com/7315/8747521283_b69fc4327d_b.jpg

http://farm9.staticflickr.com/8417/8914981944_1aa3276c1d_b.jpg

https://c2.staticflickr.com/2/1545/25073669085_7e21bba612_o.jpg

[marciero]

the article is bogus. old italian guys understood that you needed to build the race bike around the racer...those and the size of the wheels were the two constants. what that generally meant was that small bikes had steep seat angles and shallow head angles and lots of forks rake and big bikes had slack seat angles and steep head angles without much rake. i don't think you could find an italian frame builder who knows or cares about trail....especially not prior to everything moving to asia.



Are you suggesting they based their fork rake values solely on things like front-center and weight distribution? Or maybe that they knew intuitively the effect of rake and HTA on handling without specific reference to trail?

[ColonelJLloyd]

What size tires was this designed for? With tires less than 38c it is low trail.

I don't anyone who would call 50mm-53mm trail "low".

[ripvanrando]

I don't anyone who would call 50mm-53mm trail "low".

I dunno. My custom randonneuring bike has 70 mm trail. Tracks wonderfully at speed down twisties. 50mm trail seems meager to me.

[ripvanrando]

I don't know a whole lot about the technical stuff but my 62 cm 1973 Masi Gran Criterium is one heck of a nice all around road bike although I am sure one could do a Crit on it. I've actually toured on this thing, commuted to college and did some racing on it of course. The chain stays are a little long by contemporary standards. The fork has a nice graceful rake to it. The seat angle is more slack. It feels balanced. I feel out of balance on almost all modern bikes that I have ridden (except my custom Zinn). Maybe because I have very long femurs but I always have to slam the seat all the way back and that is with an offset post. I did not have to do this on the Masi or that old 531 framed English bike from the 70's that I loved so dearly. I think modern bikes neglect to account for proper seat angle in order for the bike to feel balanced but this is just my non technical view but I tend to value comfort over all else and balance is critical in my eyes.

[VC Slim]

http://farm8.staticflickr.com/7315/8747521283_b69fc4327d_b.jpg

Wow, I've never seen a drilled chainstay like that before. Must be some heavy duty tubing. Seemed oversized. Is it internally reinforced?

[FlashUNC]

Wow, I've never seen a drilled chainstay like that before. Must be some heavy duty tubing. Seemed oversized. Is it internally reinforced?

Drilled, then sleeved and the sleeves are brazed in.

In theory supposed to be stiffer, but I don't notice the difference.

[FlashUNC]

What size tires was this designed for? With tires less than 38c it is low trail.

I can squeeze a 28 in there, but its a typical 23/25 road race frame.

[dddd]

Veering slightly outside of the original topic here, but of many road bikes that I've owned and actually measured their frame angles, these few (below) stand out as having the steepest headtube angles.

Just data points here. Note that my frames range within the 56-59cm range for the most part, which somewhat rules out the need to "relax" the headtube angle for toe/tire clearance.

Most of us will have our own bias as far as what ROAD bike headtube angle falls within the normal range , depending on just what size of frames that we have been dealing with.
Today's "Endurance" geometry bikes like my Colnago CX-Zero and even my older Orbea Orca typically use headtube angles of around 72.5 degrees, while "gravel" frames will tend toward an even shallower headtube angle of around 72 degrees or less.

'52 E. Christophe "Champion de Monde", 56cm -- 76 degrees

'79 Fuji Professional 59cm -- 75 deg

'89 Basso, 58cm -- 74.1 deg

'91 Basso, 57cm -- 74 deg

'86 Triumph, 60cm -- 74.7 deg

'52 Sieber, 56cm -- 74.5 deg

'88 Merckx Corsa Extra, 59cm -- 75 deg

'97 Merckx Ti EX, 64cm -- 73.5 deg

'89 Zunow, 56cm -- 73.5 deg

'91 Merckx Century, 57cm -- 74.2 deg

'86 Nobilette, 59cm -- 74.1 deg

'88 Eisentraut Rainbow 'traut, 59cm -- 75.2 deg

'85 Centurion Elite RS, 63cm -- 74 degrees (published #)

1985 Peugeot PH501, 58cm -- 73.5 deg

Numerous late-80's Schwinn Road models, ~58cm -- 73 deg

Douglas Titanium by Lightspeed, 57cm -- 73.4 deg

1974 Peugeot PX10E, 57cm -- 76 deg (versus earlier ones at ~73 degrees!)


Just to clarify relative visual differences, here's two photos of the "steep" 1974 Peugeot lined up next to a Holdsworth Special having 73-degree angles:

https://c2.staticflickr.com/8/7152/6391899659_e100e54ded_z.jpg

https://c2.staticflickr.com/8/7173/6391900829_b1b6a34cce_z.jpg


And, a crazy-steep 1974 PX10LE having the same super-steep angles, it is a wild ride who's aggressively rider-forward positioning fully supports one's highest efforts at keeping pace amidst a better class of riders, at least for as long as I can last, ...boy is it fun when I am having a good day! Transitioning in/out of the saddle is thus effortless and quick, and even reaching for the water bottle can be an adventure in fast living!

It is only the parallax angle of the camera's position that makes the headtube angle look a bit shallower than the steep seat tube, they are actually about equal:
https://c1.staticflickr.com/9/8021/7284350756_3fc056eab9_z.jpg

As relates to our recent discussion on narrowing a cassette hub's axle spacing, here is the rear half of the 124mm-spaced 7s freewheel hub wheelset that I configured for use on the 121mm-spaced PX10LE above. It is "strong as hell" with 36 spokes, MA2 rim and as short of an axle overhang as was physically possible to use on this bike's frame. Even the French axle stops had to be heavily massaged with a Dremel stone for clearance:
https://c2.staticflickr.com/8/7076/7342076332_dba4baae22_z.jpg

[Mark McM]

If you scan down in the comments of the article you'll find Richard Sachs calling shenanigans on the claims about historical geometry.

The Frame Geometry Project (http://hiddenfortress.org/geometry/) web page has lots of bike frame geometry data from the last half century. If there's a pattern for regional or period specific geometry, I can't see it from this data - angles and fork dimension data is all over the place. If anything, it seems that modern frame geometries are far more standardized.

[Mark McM]

I People talk about geometry of different bikes as if they were polar opposites, but I've had a hard time finding these super tight geometry crit bikes of the '80s or how supposed long and slow Lemonds are.

Back in the '80s, it seems there were far more small and medium sized brands, each marching to beat of their own drummer, and so there were the few outlier companies that used their own unique geometries. A class example was Rigi (http://www.classicrendezvous.com/Italy/RIGI_main.htm), who used super short chainstays and super steep head tubes, supposedly to make their bikes more responsive. In order to achieve their super short chainstays, they used dual seat tubes, with the rear wheel tucked in between the seat tubes.

https://i.pinimg.com/736x/7d/5a/b5/7d5ab5eab268e499d8570f02ebbb7072--track-fixed-gear.jpg

[Kontact]

Back in the '80s, it seems there were far more small and medium sized brands, each marching to beat of their own drummer, and so there were the few outlier companies that used their own unique geometries. A class example was Rigi (http://www.classicrendezvous.com/Italy/RIGI_main.htm), who used super short chainstays and super steep head tubes, supposedly to make their bikes more responsive. In order to achieve their super short chainstays, they used dual seat tubes, with the rear wheel tucked in between the seat tubes.

https://i.pinimg.com/736x/7d/5a/b5/7d5ab5eab268e499d8570f02ebbb7072--track-fixed-gear.jpg

I'm aware of the Rigi and several similar designs using split or curved seat tubes. But those bikes were exceptions, just like the 75° HTA mentioned earlier. These kind of bikes were never the norm, and, like I said, I have never seen that 75° HTA anywhere.

[dddd]

Those award-winning (a very prestigious Italian design award) Rigi frames were quite possibly the most radical ever, the steepest (78x78-degrees iir) angles and very shortest wheelbase.
With that short stem the above bike must be incredibly quick-steering, methinks I'm too old to even try to ride it!
Wow.

Just WOW!

[Kontact]

Those award-winning (a very prestigious Italian design award) Rigi frames were quite possibly the most radical ever, the steepest (78x78-degrees iir) angles and very shortest wheelbase.
With that short stem the above bike must be incredibly quick-steering, methinks I'm too old to even try to ride it!
Wow.

Just WOW!

That's a good point - many of these criterium wonder machines weren't American, they were made by those same Italians that supposedly made only luxurious 72° HTA road bikes.

[dddd]

Well, the pictured Rigi is a track bike, but their "road" version might be particularly adept in a team time-trial, where the following rider can safely ride in a tighter formation to the rider ahead. So there's that.
And I've heard that these bikes take to the hills really well, though with the rider having to respect cross-chaining angle more attentively.

There were riders that won races on these bikes, though I don't recall any top team ever choosing to ride them.
And before Marco Pantani's time, alas, but can you imagine?!!!
So their potential, unfortunately, remains clouded in mystery, though their "comfort potential" would seem to be in the "slim to none" category, lol.

[paredown]

Interesting that the Peugeot from 1974 had steeper angles--I know my brother's from 1969-70 was around 73 deg as you say.

Another of the vintage frames that changed dramatically was the Raleigh Pro--the earlier ones (1970-1) were 73-ish so about like my Falcon and my friend's Holdsworth Pro, and the next iteration they also went steeper...

[Kontact]

I don't anyone who would call 50mm-53mm trail "low".

If 56mm of trail is neutral, what would you call trail that is less than 56?

I'm not making a judgement, it is just that the choices are high, low and neutral.

[Kontact]

I can squeeze a 28 in there, but its a typical 23/25 road race frame.

That's interesting that you have a low trail bike and love the handling. Most builders tend toward high for that "high speed stability" thing. But low trail is stable at lower speeds, and maybe that has a lot of utility.

Merckx apparently liked low trail because of cobbles. Should be good for steep climbs as well.

[FlashUNC]

That's interesting that you have a low trail bike and love the handling. Most builders tend toward high for that "high speed stability" thing. But low trail is stable at lower speeds, and maybe that has a lot of utility.

Merckx apparently liked low trail because of cobbles. Should be good for steep climbs as well.

The weight balance is great, rides with no hands, and plenty stable on the downhills.

Dunno, I tend towards what the jerk mentioned earlier, wheels just seem to be in the right place.

[Kontact]

The weight balance is great, rides with no hands, and plenty stable on the downhills.

Dunno, I tend towards what the jerk mentioned earlier, wheels just seem to be in the right place.

Low trail is probably the most stable with no hands - unless you are riding downhill no hands.

[exapkib]

I love this topic, and wish I understood it better than I do.

The most striking ride characteristic of my Yamaguchi (the geometry of which I wish had knew exactly) is closely tied to the tendencies that have been discussed above.

At slower speeds the steering is incredibly quick--some might say twitchy. As you move from 25 to 30 miles an hour, something changes. The steering suddenly tightens, and while the bike still changes lines quickly, it becomes stable in a most confidence-inspiring way.

I've always attributed this to some 'magic' in the bike's geometry, but I wish I could know more about which angles make the biggest difference.

The numbers that I can reliably measure:

ST: 55.2 (ctc)
TT: 55
HT: 14
Chainstay: 415
BB drop: 8.2

I'll grab the other measurements when I get home, but just wanted to throw this up there to see if any of you have had bikes with similar manners.

Thanks!

[Kontact]

I love this topic, and wish I understood it better than I do.

The most striking ride characteristic of my Yamaguchi (the geometry of which I wish had knew exactly) is closely tied to the tendencies that have been discussed above.

At slower speeds the steering is incredibly quick--some might say twitchy. As you move from 25 to 30 miles an hour, something changes. The steering suddenly tightens, and while the bike still changes lines quickly, it becomes stable in a most confidence-inspiring way.

I've always attributed this to some 'magic' in the bike's geometry, but I wish I could know more about which angles make the biggest difference.


Sounds like typical high trail behavior.

[oliver1850]

Veering slightly outside of the original topic here, but of many road bikes that I've owned and actually measured their frame angles, these few (below) stand out as having the steepest headtube angles.

Just data points here. Note that my frames range within the 56-59cm range for the most part, which somewhat rules out the need to "relax" the headtube angle for toe/tire clearance.

Most of us will have our own bias as far as what ROAD bike headtube angle falls within the normal range , depending on just what size of frames that we have been dealing with.
Today's "Endurance" geometry bikes like my Colnago CX-Zero and even my older Orbea Orca typically use headtube angles of around 72.5 degrees, while "gravel" frames will tend toward an even shallower headtube angle of around 72 degrees or less.

'52 E. Christophe "Champion de Monde", 56cm -- 76 degrees

'79 Fuji Professional 59cm -- 75 deg

'89 Basso, 58cm -- 74.1 deg

'91 Basso, 57cm -- 74 deg

'86 Triumph, 60cm -- 74.7 deg

'52 Sieber, 56cm -- 74.5 deg

'88 Merckx Corsa Extra, 59cm -- 75 deg

'97 Merckx Ti EX, 64cm -- 73.5 deg

'89 Zunow, 56cm -- 73.5 deg

'91 Merckx Century, 57cm -- 74.2 deg

'86 Nobilette, 59cm -- 74.1 deg

'88 Eisentraut Rainbow 'traut, 59cm -- 75.2 deg

'85 Centurion Elite RS, 63cm -- 74 degrees (published #)

1985 Peugeot PH501, 58cm -- 73.5 deg

Numerous late-80's Schwinn Road models, ~58cm -- 73 deg

Douglas Titanium by Lightspeed, 57cm -- 73.4 deg

1974 Peugeot PX10E, 57cm -- 76 deg (versus earlier ones at ~73 degrees!)



Add 60-62 Ritcheys to the list. Their 74 degree HTA combined with fairly low (5.17 cm) trail makes for pretty quick handling. Never measured my Basso or Centurion but think of them as being a bit more stable than the Ritchey.

[weisan]

the article is bogus. old italian guys understood that you needed to build the race bike around the racer...those and the size of the wheels were the two constants. what that generally meant was that small bikes had steep seat angles and shallow head angles and lots of forks rake and big bikes had slack seat angles and steep head angles without much rake. i don't think you could find an italian frame builder who knows or cares about trail....especially not prior to everything moving to asia.

listen- race bikes have certain constants geometrically you need to deal with, principle among them is the diameter of the wheels and you need to do your best to keep the wheelbase within range and the weight balance where it ought to be. the way to achieve this is to put the big guy between the wheels in the right place and and put the little guy between the wheels in the right place. there isn't an "italian" or an "american" geometry- there are just good race bikes and bad ones- and the good ones deal with the riders morphology and put the wheels in the right place....like that della santa posted above. i am also 100% sure there is no way Merckx rode anything like what is described as "italian" geometry in that article or anything like that picture. having seen many of his bikes they tended to be exactly what you'd expect for a big powerful guy who carried a lot of his weight in his shoulders....moderate to slack seat angles, steepish head angles (although not at the extreme) and regular fork rakes and bottom bracket drops for bike his size. look at a stock 59cm Merckx Century geometry and you get an idea.

http://alicehui.com/bike/jerk/good1.jpg

http://alicehui.com/bike/jerk/good2.jpg

http://alicehui.com/bike/jerk/good3.jpg

http://alicehui.com/bike/jerk/good4.jpg

http://alicehui.com/bike/jerk/good5.jpg

http://alicehui.com/bike/jerk/good6.jpg

http://alicehui.com/bike/jerk/good7.jpg

http://alicehui.com/bike/jerk/good8.jpg

http://alicehui.com/bike/jerk/good9.jpg

http://alicehui.com/bike/jerk/good10.jpg

[Kontact]

Add 60-62 Ritcheys to the list. Their 74 degree HTA combined with fairly low (5.17 cm) trail makes for pretty quick handling. Never measured my Basso or Centurion but think of them as being a bit more stable than the Ritchey.

74 degree head tubes are pretty common on tall bikes. It is either that or no one over 6'2" gets to hang in the corners because their wheelbase is so much longer.


I don't think it is constructive to look at HTA as anything more than a way to control wheelbase. Small bikes are going to have relaxed HTA, tall bikes steeper. Neither group has a handling advantage, both can have the same trail. Differences in wheel flop are a fairly small percentage.

[marciero]

Low trail is probably the most stable with no hands - unless you are riding downhill no hands.


My experience is the opposite of this. Is easier to initiate counter-steer with your hips with the greater wheel flop that results from higher trail. Also worth noting that higher trail generally makes a rider-less bike better able to self-right and remain upright. ("Generally" since it is possible to design a riderless bike with zero and even negative trail which can self-right.)

[ripvanrando]

Low trail is easier to ride no-hands than a high trail bike?

A well designed high trail bike is very easy to turn and very easy to ride no hands compared to low trail provided one is not climbing like a snail in which case, low trail wins in my experience.

[Mark McM]

Low trail is probably the most stable with no hands - unless you are riding downhill no hands.

I've seen many and often contradictory descriptions of how trail affects bike stability at low and high speeds. I suspect that it is difficult to make a general description, since trail is only one part of bicycle stability (the human is the largest part).

My personal preference is for low trail bikes - high trail bikes tend to want to follow their own track (be it either a straight line when the bike is upright, or in a constant curve when the bike is leaned over), and I find that I have to 'muscle' the handlebars when I want to make a quick course correction. I even find low trail bikes to more stable in a straight line, as they react less to an rocking of the bike. (Oh, and I have no trouble riding downhill with no hands on a low trail bikes.)

[cmg]

more trail, more stable, less fork rake. less trail, quicker steering, twitchy, more fork rake. i ride small frames with 72-72.5 HTA i like to use forks with 50mm rake. that's the happy medium.

[unterhausen]

I've had a hard time finding these super tight geometry crit bikes of the '80s
a couple of people have mentioned my comment in passing. I think the extreme geometry bikes were never that common, and probably got retired relatively quickly. I am not aware of any production bikes like that. When I was racing in the mid '70s to early '80s, most of us were on European brands. And there were lots of Paramounts around too. Most American builders of that era were building perfectly sensible bikes that had geometry that was very similar to European bikes of that time.


I feel like some more than one person is mixing up trail and rake. Or maybe it's my mild dyslexia.

[Kontact]

more trail, more stable, less fork rake. less trail, quicker steering, twitchy, more fork rake. i ride small frames with 72-72.5 HTA i like to use forks with 50mm rake. that's the happy medium.

This is generally not considered to be true. High trail is stable at high speeds, but twitchy at low. Low trail stable at low speeds, vague at high speeds.

Nothing is so simple as more of X is only stable. Bikes are made low trail for very good reasons.

[dddd]

I think that there is semantics at work here. People usually refer to a twitchy bike as one that darts around at high speed, not low. I would call that low-speed issue steering flop, but that's semantics as well I suppose.

And likewise I would call the low-trail bike twitchy at speed, not "vague".

But perhaps we're all trying to say basically the same things?

[marciero]

I think that there is semantics at work here. People usually refer to a twitchy bike as one that darts around at high speed, not low. I would call that low-speed issue steering flop, but that's semantics as well I suppose.

And likewise I would call the low-trail bike twitchy at speed, not "vague".

But perhaps we're all trying to say basically the same things?

The terms "twitchy" and "vague" are not necessarily in conflict or contradictory. We typically use the former to describe how the bike responds to steering input; that is, while changing the turning radius. The latter, at least in my mind, seems to suggest how the bike feels when trying to go straight or maintain a constant turning radius. The "on rails" feel that high trail bikes have cornering at higher speeds is really a resistance to changes in turning radius- equivalently, a lesser sensitivity to steering input. Low trail bikes are less resistant/more sensitive to changes in turning radius. For some riders this causes the bike to feel "vague" when maintaining a given turning radius and twitchy when actively changing the turning radius.

[ripvanrando]

Low trail bikes have a tendency to shimmy at speed compared to high trail bikes although a leather clad handlebar bag and wide supple tires tend to mitigate as does the fat of a chubby rider, especially if wearing a blue woolen jersey. It is a system. Not just the bike. We don't have the equations or the eigenvalues; so, we all just worship at our respective alters.

[dddd]

The terms "twitchy" and "vague" are not necessarily in conflict or contradictory. We typically use the former to describe how the bike responds to steering input; that is, while changing the turning radius. The latter, at least in my mind, seems to suggest how the bike feels when trying to go straight or maintain a constant turning radius. The "on rails" feel that high trail bikes have cornering at higher speeds is really a resistance to changes in turning radius- equivalently, a lesser sensitivity to steering input. Low trail bikes are less resistant/more sensitive to changes in turning radius. For some riders this causes the bike to feel "vague" when maintaining a given turning radius and twitchy when actively changing the turning radius.

You described all of that pretty well.

I had one steep-angled bike that was a bit on the big side and I used a 9cm stem on it. I would often steer into higher-speed corners only to have my trajectory come in too far too early, so I often took such corners in a less-than-smooth line at more cautious speeds. I thought the the trajectory "vagueness" was in my head until I downsized to a smaller frame of the same model (1991 Specialized Epic) and fitted a 10cm neck. The second bike handled just about perfect and I still have it! I still call the first bike twitchy though, if only because I think it's what the term means to the most people.

[Mark McM]

The terms "twitchy" and "vague" are not necessarily in conflict or contradictory. We typically use the former to describe how the bike responds to steering input; that is, while changing the turning radius. The latter, at least in my mind, seems to suggest how the bike feels when trying to go straight or maintain a constant turning radius. The "on rails" feel that high trail bikes have cornering at higher speeds is really a resistance to changes in turning radius- equivalently, a lesser sensitivity to steering input. Low trail bikes are less resistant/more sensitive to changes in turning radius. For some riders this causes the bike to feel "vague" when maintaining a given turning radius and twitchy when actively changing the turning radius.

Furthermore: The steering inputs required to keep a bike in balance (either in a straight line or in a turn) vary with speed. A steering input which causes a small lateral deflection at low speed will cause a much larger lateral deflection at high speed. And steering trail acts to oppose steering inputs

At low speed, large steering inputs are required to stay in balance, and since trail tends to oppose steering inputs, a bike with high trail may seem "unstable" at low speeds, because the rider has to work harder to apply the steering inputs to keep it in balance. A bike with low trail will react more readily to steering inputs, making it easier for the rider to provide the steering inputs to stay balanced.

At high speeds, a bike which reacts quickly to steering inputs may feel "unstable", because the bike may have large reactions to even the smallest steering inputs. A bike with low trail may therefore feel "twitchy" at high speeds. With high trail, the bike reacts less to applied steering inputs, so will better tend to stay on track, both in a straight line and when turning.