Arboleda

Let's ignore the the wind resistance that would be increased with a larger body size.

That ignored, would a 150 lb. rider attain the same average speed over a long distance as a 250 lb. rider if they're both putting out the same power?

spinerguy

I believe, *if* they are putting out same power, skinny pants would have significantly higher average speed.

Kind of Blued

This will give you an idea: https://bikecalculator.com/veloUS.html

On the flats, a skinny guy would go a little faster. As the road goes up, the skinny guy would go a lot faster. As the road goes down, the heavier guy goes faster.

znomit

Lets not.

carpediemracing 

My weight fluctuated severely over the last two years. I'm 5'7" and not tall on the bike.

At 180-200 lbs, I was okay but not great, put down the most amount of power (260+ watts FTP). The next year, at 155-160, I had the second best year of my life, in 20-odd years of racing (best year was a long time ago, at 133-135 lbs). I put down less power (210? watts FTP), had a weaker sprint usually (in pure power terms, rarely breaking 1200w), but won more field sprints. Finally, at 165-175, I had a bad year, with similar power numbers to my 155-160 lbs year.

Since I climb as well as an NFL linebacker, I studiously avoid races with much of a hill (over 30-40 seconds worth of climbing every couple minutes of racing). I climb hills in training, up to 120 minutes long. What I'm saying is that I ride flat roads the majority of the time, and I measure my "riding worth" on flatter roads.

Given the choice, I'd rather be lighter than I am now. 155-160 was good, even if I was weaker overall.

William I am

Seems like weight is never negligible.

Given the two guys are outputting the same power (I would expect the heavier guy to put out more power, but not necessarily)
Force due to friction = (normal force)*(coefficient of friction)
Not only would the heavier guy have increased normal force (force downward), but the tires would probably flatten more, making more of the tire contact the road at once. The increased contact patch would increase the coefficient of friction as well.

I'd say you could equate the question to "does riding with underinflated tires increase drag?".
Cheers!

LazinCajun

The heavier guy would likely be running higher pressures, so the contact patch argument isn't quite as simple as you state it. Any effects like that will be much smaller than say, the difference that weight makes on hills (obviously).

Plus, friction at the tire/road surface isn't a bad thing. Thought experiment: imagine 2 identical riders/bikes having a quick race. The only difference is one is on super-slippery ice, the other on asphalt (assume the ice rider doesn't fall). Who gets to the finish line first? Clearly, the one on asphalt -- the guy on ice just spins his rear wheel without moving! It turns out that with idealized wheels/tires (ie, no slippage), the friction at the road causes no loss of energy for rolling objects.

Rolling resistance losses are due to things like tire flex (remember: higher pressures for the heavier rider will make this more complicated) and also friction in hubs/bearings/drivetrains/etc., but definitely NOT the friction between tire and road.

Looigi

If weight is a disadvantage up hill and an advantage down hill, there exists a slope between those two where the light and heavy rider would go the same speed for the same power output. (Mean value theorem...sort of).

thump55

150lb vs 250 lb at 200 watts (flat, no wind) = .76 mph difference according to my calculator.

Not as much as you think...however, at only a .5% gradient, the difference is 1.49 mph.

hhnngg1

I think more importantly, odds are that a 250lbs guy will be as fit as the 150lbs guy are low. He'd have to be like 6"6+ or something like that compared to the 150lbs guy who could be 5'6" and still be 'light'.

pallen

I find that I can often outrun people on the flats who outclimb me - especially when there is a headwind. I chalk it up to inertia. Its that or the aerobelly.

Grumpy McTrumpy

the current world hour record was set by a very large rider on a heavy bike with special weighted wheels.

https://www.wolfgang-menn.de/sosenka.htm

wphamilton

That slope would be "0" I think, or close to 0 if you factor in a larger frontal area.

If we consider the squared resistance at higher downhill speeds we see that the lighter rider with the same power always has an advantage in velocity over the circuit if uphills and downhills are symmetrical.

to add: since the rolling resistance is negligible at higher speeds I think the difference due to weight alone is negligible on flats. Other things being equal though the larger guy usually has more power giving him the advantage.

gregf83 

If you ignore wind, the 250lb rider will lose at least 20W due to higher rolling resistance so he will be slower.

In general, with equal power, the lighter rider will win by a wide margin as the heavier rider will either be fat and unable to reach an aero position or tall and have higher drag.

If the heavier rider is lean and has the same power/weight ratio then the heavier rider can be faster if he has a decent aero position.

Homebrew01

Surprising he didn't use aero wheels

ColinL

Problem with this example scenario:

assuming similar levels of fitness, the heavier rider usually puts out more power. this can't be a surprise..

seypat

Aerobelly! Love it!

seypat

No coincidence that the fastest riders are not the 130-140 flyweights.

WhyFi

This is neither here nor there, as the OP specifically said that the only variable was weight. In any event, there are plenty of un-fit 150-pounders, too. Oh, you're also bringing BMI in to your conversation and BMI isn't useful on an individual level. And if you want to talk about odds being low, how about the odds that the 250 lb guy only puts out as much power as the 150 lb guy?

gregf83 

Aero wheels aren't allowed in the UCI hour record attempt.

UC223

exactly... At 190lbs i have to work like hell to go up hill with the skinny guys, but put me on a flat road (even with increased wind resistance) and the difference in power becomes quite noticable.

Matt Gaunt

I might have missed the point here, but if the two people are putting out the same power, then the smaller of the two would surely be quicker because he is moving less weight.

Power = work done / time taken.

In this case, the constant power output (for both riders) is fuelling the propulsion of different masses. The time variable cannot be the same for both.

gregf83 

Actually power = work / time. The only reason the smaller rider goes faster is because the rolling resistance is less.

Matt Gaunt

I spotted my typo and corrected it - thought I'd got away with it too!

rpeterson

You're absolutely right, but people grossly overestimate how much of a difference it actually makes.