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  #1  
Old 09-15-2005, 12:36 PM
KevinK KevinK is offline
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Talking Inertia while climbing

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!

Kevin
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Old 09-15-2005, 12:54 PM
RichMc RichMc is offline
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That might be significant if the rider is a pro and is racing for money. Otherwise ..............................? (IMO)
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Old 09-15-2005, 01:16 PM
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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.
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Old 09-15-2005, 01:24 PM
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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.
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Old 09-15-2005, 01:31 PM
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Quote:
Originally Posted by 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.

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


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Old 09-15-2005, 01:38 PM
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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.

Last edited by weisan; 09-15-2005 at 01:42 PM.
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Old 09-15-2005, 01:40 PM
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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?
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Old 09-15-2005, 01:46 PM
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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.
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Old 09-15-2005, 01:49 PM
KevinK KevinK is offline
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Quote:
Originally Posted by 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.
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
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Old 09-15-2005, 01:50 PM
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Quote:
Originally Posted by 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.
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.
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Old 09-15-2005, 01:59 PM
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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.
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Old 09-15-2005, 02:07 PM
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Weisan: I will let you know when I get my custom spectrum Ti with a sloping top tube....

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

Last edited by znfdl; 09-15-2005 at 02:19 PM.
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  #13  
Old 09-15-2005, 02:14 PM
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Dopers are faster than slopers.
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  #14  
Old 09-15-2005, 03:41 PM
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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.

Last edited by zap; 09-15-2005 at 05:01 PM.
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  #15  
Old 09-15-2005, 03:46 PM
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mass, zap, mass.
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