What is the truth behind bike weight? Does it really help THAT much?



Eden

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TheDarkLord said:
Yeah, that's true. To clarify, the force felt by the rider during a curve is centrifugal force, while the actual acceleration itself (due to change in velocity) is directed in the opposite direction and is called centripetal acceleration. So, I guess the coefficient of friction is the primary factor when it comes to cornering without the tire washing out. So, why would a heavier rider be able to corner better?
confused0006.gif

Now when I was discussing that I felt more stable with all that weight in my bag with my husband, we also thought it might have something to do with the distribution of the weight as well as the fact that there was more of it. We thought where the bag was sitting was possibly changing my center of gravity enough to make the bike feel stickier in the corners.
 

Crankyfeet

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dhk2 said:
Actually, that's the reason us heavier guys don't have an advantage in the hills. For the same power, that extra kg we drag up that steep hill costs a straight % of our total weight, while going down, we only get the square root of that % back.
The heavier guys just get square rooted... :p
 

Crankyfeet

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I think the ramifications of this debate so far are clear. If you can somehow get two water bottles full of sand and a full messenger bag from your team at the top of the hill... it could make things a lot easier on the descent. That doesn't break any rules... does it?... :rolleyes:
 

dhk2

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Aug 8, 2006
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TheDarkLord said:
Yes, it agrees with theory. I was gonna post this before, but was waiting for your input regarding the parameters you used... I posted yesterday that for a drag force that is dependent on velocity, the terminal velocity is proportional to mass. Wikipedia has an approximate analytic solution for the case where the drag is proportional to velocity square (involving hyperbolic functions; you can see it here), and as you say, the terminal velocity is proportional to the square root of mass. So, a 1% reduction in weight will give rise to 0.5% reduction in terminal velocity.

But is it really true that the power output of a heavier rider is proportional to the weight (Cranky's post)? Don't see why climbers like Chicken would be so lean then...
The drag power is a function of velocity cubed, but since the "power input" on a descent is also a function of velocity, when equating the two sides to solve for steady-state velocity, I get the following function of v squared:

V **2 (m/sec) = (2*kg*9.8*Gradient)/ (rho*cdA)

Believe in general a bigger, heavier rider will have more power output, but excess body fat doesn't contribute to that power. So, for top pro's already at their peak power development, getting down to minimum healthly bodyfat is necessary to optimize their power-to-weight ratio.
 

dhk2

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Crankyfeet said:
I think the ramifications of this debate so far are clear. If you can somehow get two water bottles full of sand and a full messenger bag from your team at the top of the hill... it could make things a lot easier on the descent. That doesn't break any rules... does it?... :rolleyes:
Good plan. On the way up, you can also throw your two water bottles to your support crew, saving up to 1.5 kg, and have them handed back at the summit.

It is fun to pass the lighter guys on the descents, but the cruel reality of the physics is hard to overcome without superior fitness or wheel-sucking skills. Last weekend, I was smoking by a 150 lb guy on his new 46mm Reynolds tubie super wheels....at 40 mph, my extra 35 lbs beat his expensive aero wheels hands down :)
 

Crankyfeet

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TheDarkLord said:
But is it really true that the power output of a heavier rider is proportional to the weight (Cranky's post)? Don't see why climbers like Chicken would be so lean then...
I wasn't saying that power was proportional to weight. I was showing an example where this was the case to illustrate how the effects of extra power can compensate for the disadvantages of extra weight on the upslope... but you get an advantage with both power and weight on the downslope.

My point was not that power is proportional to weight.
 

Crankyfeet

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dhk2 said:
Good plan. On the way up, you can also throw your two water bottles to your support crew, saving up to 1.5 kg, and have them handed back at the summit.

It is fun to pass the lighter guys on the descents, but the cruel reality of the physics is hard to overcome without superior fitness or wheel-sucking skills. Last weekend, I was smoking by a 150 lb guy on his new 46mm Reynolds tubie super wheels....at 40 mph, my extra 35 lbs beat his expensive aero wheels hands down :)
If only some races were just downhills intermixed with some flats (no uphills). You could get an entirely different physical specimen who specializes in these type of races... :rolleyes: :p
 

dhk2

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Crankyfeet said:
If only some races were just downhills intermixed with some flats (no uphills). You could get an entirely different physical specimen who specializes in these type of races... :rolleyes: :p
Actually, it is surprising how strong some overweight cyclists are on the flats. I've learned never to judge a rider by first appearances.....that big guy with 30 lbs of extra bodyfat is great to draft behind, and may just end up pulling you home at 22 mph :)
 

Crankyfeet

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dhk2 said:
Actually, it is surprising how strong some overweight cyclists are on the flats. I've learned never to judge a rider by first appearances.....that big guy with 30 lbs of extra bodyfat is great to draft behind, and may just end up pulling you home at 22 mph :)
The extra weight can give them more momentum that makes it easier to sustain speed into a headwind. Same as the flywhel effect in a car (though that is mainly to sustain momentum during gear changes). And under that fatty cushioning, there might be some serious muscle that remains hidden from view... :)
 

sogood

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dhk2 said:
Actually, it is surprising how strong some overweight cyclists are on the flats. I've learned never to judge a rider by first appearances.....that big guy with 30 lbs of extra bodyfat is great to draft behind, and may just end up pulling you home at 22 mph :)
I agree, especially on a typically flat criterium course.
 

TheDarkLord

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Crankyfeet said:
If only some races were just downhills intermixed with some flats (no uphills). You could get an entirely different physical specimen who specializes in these type of races... :rolleyes: :p
I'm thinking of that super-fat rider that you posted in the FID thread. :p

But sure, a heavy rider picks up more momentum going downhill, but if there is a flat stage after a downhill, how long will that advantage last? The increased air drag, etc. should kill off the advantage after a while, right?
 

swampy1970

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Feb 3, 2008
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TheDarkLord said:
I'm thinking of that super-fat rider that you posted in the FID thread. :p

But sure, a heavy rider picks up more momentum going downhill, but if there is a flat stage after a downhill, how long will that advantage last? The increased air drag, etc. should kill off the advantage after a while, right?
.... and what about the braking distances? Even Dura Ace calipers aint gonna do too well if you're talking "that super-fat rider that you posted in the FID thread" - disk brakes front and rear me thinks with custom super soft compound slick tires.
 

TheDarkLord

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swampy1970 said:
.... and what about the braking distances? Even Dura Ace calipers aint gonna do too well if you're talking "that super-fat rider that you posted in the FID thread" - disk brakes front and rear me thinks with custom super soft compound slick tires.
If it is a really long descent, even disk brakes may not help, and drag brakes may be required - of course not feasible in a race (which would disqualify the "super-fat dude" from participating in such a race me thinks :p ). It is the same problem with tandems - can't use rim brakes or even disk brakes for long descents.
 

artemidorus

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swampy1970 said:
.... and what about the braking distances? Even Dura Ace calipers aint gonna do too well if you're talking "that super-fat rider that you posted in the FID thread" - disk brakes front and rear me thinks with custom super soft compound slick tires.
DuraAce Calipers=105 calipers. It's the pads and rims that make all the difference.
 

swampy1970

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TheDarkLord said:
If it is a really long descent, even disk brakes may not help, and drag brakes may be required - of course not feasible in a race (which would disqualify the "super-fat dude" from participating in such a race me thinks :p ). It is the same problem with tandems - can't use rim brakes or even disk brakes for long descents.
So how do tandems get down mountains then? Do the riders make like Fred Flintstone and Barney Rubble and don some slate soled shoes and give it some serious foot on floor action? :eek:
 

TheDarkLord

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Dec 24, 2007
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swampy1970 said:
So how do tandems get down mountains then? Do the riders make like Fred Flintstone and Barney Rubble and don some slate soled shoes and give it some serious foot on floor action? :eek:
If it is a really long descent, they use drag brakes.
 

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