Weight and bike speed ratio

I would think it would depend in good measure on the course. Formula's going to be different on a 12% uphill than on a flat course or a 12% downhill, isn't it?

Stop thinking and go ride. Oh yeah, drop some poundage while you're at it. You'll still be sexy (yeah, right) when you're little.

Why the "Resident Curmudgeon" tag?  Oh wait....nevermind

I think there are way too many variables that you have to assume are constant to get any sort of ratio based on weight vs. speed.  For example, if you're assuming that the rider weight is reduced (presumably through exercise?), then it might not be reasonable to assume that power output would be constant, since you'd normally improve fitness in the process.  You'd also have to assume same course, same environmental conditions, etc., etc.

But I guess if you could do it and if you assumed that all weight counts, not just body weight, then you could figure out how much faster you'd be riding naked.  That might be interesting...

Bripod - 2008-03-17 7:07 PM All I know is that when I was out riding with two other guys who didn't weigh as much as I did I coasted down the hill faster! So that's gotta count for something They wanted to blame my bike, but I say it's force=mass x velocity.

close: your weight being higher produces more propulsive force during downhill travel (F=ma, a being due to gravity) and your aero drag being about the same as theirs means that you will see a higher coasting velocity than they will. There's even a non-dimensional measure called ballistic coefficient, which is essentially the ratio of weight to drag. Higher the ballistic coefficient, the faster the object goes before the drag force causes it to stop accelerating.

mac - on the flats it's not gonna make that much difference because once you are up to speed most of the resistance is due to aero drag, which is not a function of mass. On uphills it makes a big big difference since you are now fighting gravity to pull the mass uphill. On downhills, the heavier object will have the speed advantage (all other things being equal).

I think this is the big reason why in a bicycle stage race the "big guys" (relatively speaking) do well on the flattish sprint stages and the better climbers tend to be the "little guys."

Your example is true in a vacuum.  Outside the vacuum, air resistance comes into play.  All other things equal, the heavier object will be able to better overcome air resistance and reach a higher terminal velocity.

(I think.)

Whenever I ride in group rides and races I pass people left and right going downhill and then they pass me right back as we head back up the next climb.  In Louisiville last year I played leap-frog with another rider like 12 times on the rolling hills.  I'd pass her on the down and she pass me back on the up.

It's not  a zero-sum-game though as it's simply takes more energy to move a bigger mass over a given distance.  Sunday I biked 50 miles and averaged 16.47 mph.  I'm 265 lbs.  If I would drop 50 lbs, I could probably average 29 mph!  OK, probably not....but I'd be much faster for sure.

~Mike

yup, well said Johnny

Not at all. It would have to have a lot more descents for you to spend more time going downhill than up, which is the only way being heavier would be an advantage.

I rode in Denali National Park one time and we biked uphill for about a mile and then rode downhill the next 15 miles.  It was awesome!  Not a race of course, but a really fun ride.

~Mike

I've often thought in Tahoe that they should run the ski lifts in the summer for bicycles, especially coming down off of Spooner Junction going south.

but if I ride lots then I will lose weight and, thus, my downhill speed advantage

I need a Twinkie