Inertia while climbing

[KevinK]

Tom Kellogg says about compact frames (snipped from a previous thread)

<snipped> The big change came when I stood to accelerate or climb. As I stood up, the bike appeared to loose three pounds. The inertia of the bike as I rocked it back and fourth was reduced so much that I felt as though I was on a twelve-pound bike. Interestingly, when seated, a compact frame feels exactly like a traditional design. The compact design has no effect on handling beyond the increases responsiveness during climbing and accelerating.</quote>


That lowering the toptube reduces the inertia of the frame and makes it easier to throw from side to side is an interesting (and I believe supportable)observation. It makes sense that as the mass is moved closer to the rotational center, total system inertia is reduced relative to that center. So if one does alot of out-of-the-saddle climbing, as I do, the mass of components such as seat, post, bars, stem and levers becomes doubly important, as these are the components farthest away from the rotational center of a bike being rocked side to side. Lightening up these components will reduce effects of gravity, as well as reduce overall inertia (albeit only when rocking the bike). And the weight of the contents of your under saddle bag or (heaven forbid) seat mounted water bottles is really killing your climbing ability. Makes me want to rethink my setup, from the top down. I hear a new seat and post calling my name! :D

Kevin

[RichMc]

That might be significant if the rider is a pro and is racing for money. Otherwise ..............................? (IMO)

[znfdl]

RichMc:

It depends upon the type of riding one does. For example, my favorite type of ride is in excess of 100 miles riding over mountain passes. I like to climb in and out of the saddle. Any saving of energy over a long ride would be wlecome.

If one were to go on a 20 mile ride with rolling hills and taking it easy, you are right that the difference in inertia would not make much of a difference.

[bostondrunk]

I don't think gravity is gonna make much difference if your top tube is a few inches lower to the ground.....please.....
It makes perfect sense that the bike -feels- different when out of the saddle because the weight of it is lower to the ground. But its just how it feels. You ain't gonna go uphill faster.

[William]

I don't think gravity is gonna make much difference if your top tube is a few inches lower to the ground.....please.....
It makes perfect sense that the bike -feels- different when out of the saddle because the weight of it is lower to the ground. But its just how it feels. You ain't gonna go uphill faster.


I'll bet it would if you put a six of Old Rasputin at the top. Oh, sorry BD, make that MGD. ;)


William :beer:

[weisan]

Did Lance resort to this trick when he is givin' Jan, who's riding a sloping giant, a beating on the Ax-3 Domaines mountain stage? Did he feel disadvantage to Basso who's riding a sloping Cervelo and both ended the stage on same time?

Obviously, Lance is Lance...if we mortals "feel" better when climbing on a bike with a sloping tube, we shouldn't let anything stop us.

[Argos]

There was an article a few years ago in a European Cycling Mag about this, and how a lot of the spaniards were on a kick to have compact frames and LIGHT(!) seat and seatposts (I believe at the time there was a surge for AX Lightness products).

I've even heard this as a valid reason for sprinters to use a lighter saddle.

Myself, I would say yeah, if you are not a pro, then comfort really should come first, especially for climbers, as you are not throwing the bike back and forth so fast, nor does it matter. If you would LIKE to lighten things for this reason, it is completely your perogative.

I may be inclined to say that for a CAT 4 trying to move up or CAT 3 and above trying to get every inch out of his sprint, it may be important, especially when you have not done it and you lose by a wheel.

In sprinting the cadence is much higher, and the saddle (for example) is swinging back and forth very quickly, and very often. If you take a 135gm saddle vs a 260 gm saddle and they have 80-100 oscillations covering 16 inches total (8 inches off center, c'mon I'm just guesstimating..) during a period of 45 seconds of intense effort, I would think that haveing to move the 130 extra grams at the top of the mast all the way to the left, stop it's motion, and swing all the way to the right, repeat, repeat, for every pedal stroke cast in anger, could measure to a few watts over the course of the last 250 meters.

What are some thoughts on this? Again, my view is it is minimal, but existant, and could be a half a wheel length. Any Mathmaticians? :bike:

[znfdl]

Weisan:

The question you should be asking would Lance perform differently on a sloping top tube bike versus a level top tube bike all other things being equal.

Comparing one individual on a bike to another individual on a different type of bike would not be a meaningful comparison,as you could not control for the rider.

Just my 2 cents.

[KevinK]

I don't think gravity is gonna make much difference if your top tube is a few inches lower to the ground.....please.....
It makes perfect sense that the bike -feels- different when out of the saddle because the weight of it is lower to the ground. But its just how it feels. You ain't gonna go uphill faster.

I believe that if you can reduce the inertia, then you will be reducing the work needed to start or keep the object in motion. Since rocking the bike side to side while climbing is a start-stop-start-stop motion, I can see where reducing the inertia of the bike to this motion will help the rider conserve energy. That being said, I'm not absolutely certain whether the rocking motion is a result of mashing on the pedals (in which case more inertia and less rocking may provide a more stable platform on which to mash) or if throwing the bike side to side makes you a more effiective pedal masher. I tend to believe that rocking the bike helps get me up the hill faster, and that reducing the inertia makes it easier to rock the bike, and therefore, reducing inertia helps get me up the hill faster. BTW, I ride a level TT.

Kevin

[flydhest]

I don't think gravity is gonna make much difference if your top tube is a few inches lower to the ground.....please.....
It makes perfect sense that the bike -feels- different when out of the saddle because the weight of it is lower to the ground. But its just how it feels. You ain't gonna go uphill faster.

bd,
no one was talking about the weight of the bike, but the placement of the mass relative to the center plane of the bike. Presumably, the argument is that moving the mass side to side uses energy and that the further from the ground the mass is, the more energy the side to side movement requires because it will be traveling a further distance. So it's not weight so much as mass.

[weisan]

z-n-f-d-l-p-a-l, it's an interesting question....but personally, I don't think the difference is as big as one may think.

[znfdl]

Weisan: I will let you know when I get my custom spectrum Ti with a sloping top tube.... :cool:

I can then compare the sloping top tube bike with my level top tube spectrum Ti.

[Johny]

Dopers are faster than slopers.

[zap]

OK, I have horizontal tt on my light bike but do have an '05 Easton EC90 post and an AX Lightness Apollo saddle. Combined weight of saddle, seatpost and misc. grease is 222 grams +/- 1%. I also do not use a saddle bag.

Is it easier to flik side to side than my other bikes with heavier seat and post? Maybe, but I can't say with any certainty. The whole bike feels different compared to my other rides.

But the physics makes sense, so flikability should improve. Mass is mass and more is not better.

[flydhest]

mass, zap, mass.

[Fixed]

Bro it's all in your head.i.m.h.o. Cheers :beer:

[Ray]

Weisan: I will let you know when I get my custom spectrum Ti with a sloping top tube.... :cool:

I can then compare the sloping top tube bike with my level top tube spectrum Ti.
I have a Spectrum Ti with a sloping top tube and also a Rivendell and RB-1 with traditional top tubes (and heavier ones to boot). On the Riv, I frequently ride a Brooks saddle, which is WAAAAAY heavier than the Aliantes I have on the others. I can tell a slight difference with the brooks saddle, but it doesn't seem to detract from the experience at all - it just feels different. I can't tell the difference rocking the RB-1 and the Spectrum at all.

It might make a small measurable difference for someone who spends a LOT of time out of the saddle, but it doesn't change the feel of the bike much if at all.

-Ray

[KevinK]

I just went out for a hard lunch ride, with 2 short hard climbs and 2 sprints. I observed that when I am pounding out of the saddle, I am throwing the bike to the opposite side of my pedal stroke. In other words, when I am pushing down on my right pedal, I am pushing the bike to the left. This action is needed to counteract the tendancy for the bike to lean to the side of the pedal stroke. push down right, throw bike left, push down left, throw bike right. So, it would seem that greater inertia would be beneficial by reducing or at least slowing down the tendancy for the bike to lean into the pedal stroke. So, just maybe, the lower inertia created by sloping TT, light saddle and post etc. may feel livelier because the bike responds quicker to each pedal stroke, but it may actually be creating more work for the rider by increasing the effort needed to counteract the quickness of the leaning action caused by the pedal stroke.

Or not... :confused:

Kevin

[bostondrunk]

biopace rules (as does white shimano sante).
and yer all idiots.












:beer:

[vaxn8r]

biopace rules (as does white shimano sante).
and yer all idiots.

Mmmmmmm....two of my favs. Thanks for the mental picture!

[RichMc]

mass, zap, mass.


Fly,

The important thing to remember in this discussion is where the mass is located. (Since the frame materials in question are near to the same weight in this application it is almost the same thing to speak of mass and weight as being identical, although they are different).

I think if you were to test where the actual center of gravity is on a frame you would be quite surprised that they are nearly identical. There is a pretty fun test that could be easily done for those so inclined. (no pun intended).

The rocking motion is controlled by the rider. I bet that lots of rocking motion is a lot of wasted energy. I have found that if I concentrate on holding the bike as steady as I can and put more direct effort into the leg stroke that it seems that I climb more efficiently. That could be all in my head too.

Throwing the bike when climbing or sprinting is a lot like yelling out loud when lifting weights. It feels good but doesn't necessarily make you stronger.

I have a sloper, a partial sloper, and a horizontal top tube. Can't feel the difference in any of them really and truly.

But the bottom line is that you should go with whatever floats your boat. Cheers.

[Dave]

What baloney. I alternate between a conventional frame and a sloping frame, riding the Colorado mountains and I've never noticed any difference.

There can't be more than an ounce or two difference in the weight.

[Argos]

That, Dave, is why I think it would matter more in a 250-400 meter sprint more then climbing. Faster, more dramatic swinging.


I've devised this test for all of us. Hold an average brick over you head, arms straight, and swing in left to right 20 times as fast as you can moving from over your head to over each shoulder.

Now repeat with a cinder block. :D

[Needs Help]

Presumably, the argument is that moving the mass side to side uses energy and that the further from the ground the mass is, the more energy the side to side movement requires because it will be traveling a further distance. So it's not weight so much as mass.
Since he is talking about riding bicycles on the planet Earth, it's all about weight.

Work(energy) = Force x displacement

The Force under discussion is the weight of the bike and the displacement is how far the center of gravity moves. A bike with a lower center of gravity would presumably move through a smaller arc as it was rocked back and forth.

The rocking motion is controlled by the rider. I bet that lots of rocking motion is a lot of wasted energy. I have found that if I concentrate on holding the bike as steady as I can and put more direct effort into the leg stroke that it seems that I climb more efficiently. That could be all in my head too.

Throwing the bike when climbing or sprinting is a lot like yelling out loud when lifting weights. It feels good but doesn't necessarily make you stronger.
It seems to me that rocking a bike while climbing or sprinting is a means of bringing your upper body into the pedal stroke, so I don't think it's anything like yelling while lifting weights. It may not be as efficient as staying seated or not rocking the bike, but I think it's employed as a means of going faster, and it's also a way to use different muscle groups. You have to remember that at the end of a race, the winner isn't determined by notions of who was the most efficient, it's who went faster.

[The Spider]

so if mass is mass...then you wouldn't care where your bidons go?

one of the things I stipulate in a custom frame is that the bottome bolt for the cage is 165mm from BB shell so that the bidons are as low as possible for a lower center of gravity (for the bike...I weigh 180 pounds!).

I think lowering the weight (as in position, not the actual number) does alter the feel of the bicycle.

Lowering the weight of the bicycle is felt in the back pocket too! :)

[bostondrunk]

What baloney. I alternate between a conventional frame and a sloping frame, riding the Colorado mountains and I've never noticed any difference.

There can't be more than an ounce or two difference in the weight.

what he said

[flydhest]

needs help,

first, I was twitting zap. second, mass is actually the point since we're not talking about counter-acting the force of gravity (in which case the two would be indistinguishable) but counter-acting side-to-side motion, which is independent of gravity.

[Sandy]

That, Dave, is why I think it would matter more in a 250-400 meter sprint more then climbing. Faster, more dramatic swinging.


I've devised this test for all of us. Hold an average brick over you head, arms straight, and swing in left to right 20 times as fast as you can moving from over your head to over each shoulder.

Now repeat with a cinder block. :D

Such a lousy test!! I tried the test because I believe in you. I was doing ok with the brick up to about 12-15 swings, but then I started to get tired and the brick was getting heavy. Swings 18-20 resuted in smashing my head and ears into a swollen black and blue mess.

But you are a respected and likeable Forum poster, so I tried it with the cinder block. Bad idea! Really bad idea! I lifted (sort of) that cinder block over my head but was unable to support its weight. The cinder block fell out of my hands and smashed my beautiful head, causing a big gash and severe pain that travelled all the way down to my toes. I am in the emergency room with a swollen head, waiting patiently for the doc to sew up my head!! :)

Sewing Stiches Serotta Simpleton

[zap]

Sandy, put the brick on the saddle, sprint, then report back to us.

[toaster]

I'm waiting for someone to fill a bottle with pills and name them Climb-Tabs or Climb-Endurox and then type up some ad copy explaining how the science of thermogenic properties combined with electrolyte replacement and free radical oxidation will allow the user to lose more weight while riding up grades as they move faster and actually gain minutes on their usual climbs lasting 20 minutes or more.

It would be better to make those psycological changes to a rider's head than to mess with his top tube.

[Tom]

What you need is a counter-inertial mechanism so that when the top tube is going left, the C.I.M. is going right and vice versa. It all cancels out and you scoot up the hill like you're on the wings of Mercury.

What everybody needs is the Ambros Sinusoidal Counter Acting Mechanism! ASCAM will give you everything you need to out-duel your riding pals. Yes, ASCAM is the answer.

[Argos]

Sandy,

Great post, good laugh!

[chrisroph]

Comparing my sloping spectrum ti to my non-sloping serotta legend, the difference between them in out of the saddle climbing is so huge as to be almost noticeable.

[Needs Help]

mass is actually the point since we're not talking about counter-acting the force of gravity (in which case the two would be indistinguishable) but counter-acting side-to-side motion, which is independent of gravity.

Weight and mass are not indistinguishable, and nothing on the surface of the planet Earth is independent of gravity.

If the two bikes are identical except that the sloped top tube bike has a lower center of gravity(i.e. the bikes weigh the same but one bike's weight is closer to the ground) and the same person rides both bikes and climbs with identical form, then the only difference will be the affect of gravity on the bike as it is rocked back and forth.

[flydhest]

Weight and mass are not indistinguishable, and nothing on the surface of the planet Earth is independent of gravity.

If the two bikes are identical except that the sloped top tube bike has a lower center of gravity(i.e. the bikes weigh the same but one bike's weight is closer to the ground) and the same person rides both bikes and climbs with identical form, then the only difference will be the affect of gravity on the bike as it is rocked back and forth.

whazzajiggyhuh???

The rocking back and forth . . . first, despite, as you point out, that gravity does pull on things, abstract from gravity for a second. Moving an object side to side requires force. That force is a direct function of the mass of the object. Starting on the left, one must accelerate it into motion F=MA. At the right end, you have to slow it to a stop . . . F=MA again. Then you have to move it back to the left. All of this independent of gravity. Now, put gravity back in the picture, you have to hold it up against gravity, but that doesn't change the fact that you have to accelerate the mass side to side, this latter part being completely independent of gravity. Now, to the extent that the object is moving in an arc and not flat side to side could introduce some effect by moving in the vertical plane, but that's less than second order.

what does that first sentence mean, anyway?