Originally Posted by StephenH

I was playing around with the numbers on this site:
Bike Calculator

Suppose your course is 85 miles of level, 7.5 miles of 5% uphill, 7.5 miles of 5% downhill, no headwind, 70 degrees, 500' above sea level elevation, constant power output the whole time.
Mr Heavy is 240 lbs on a 25 lb bike.
Mr Lite is 140 lbs on a 20 lb bike.
Suppose both average 16 mph over this entire course, riding on hoods the whole time.
I would call that "comparable riders".
Well, Mr Heavy requires 176 watts power. That's 0.733 watts/lb.
Mr Lite requires 138 watts power. That's 0.985 watts/lb.
So first note, "comparable riders" don't necessarily have the same power output, or the same output per pound of body weight.

Next, assume both are putting out that same output, but riding on level ground into a 20 mph headwind.
Mr Heavy can go 8.64 mph or, if he has aerobars, 11.38 mph.
Mr Lite can go 7.64 mph or, if he has aerobars, 10.22 mph.
So riders that are comparable in that first course, the heavier rider can handily leave the lighter in a headwind.

Next, assume both start up a 5% grade, no wind, same power level.
Mr. Heavy can go 5.65 mph.
Mr. Lite can go 7.08 mph.
So the lighter rider can handily outclimb the heavier rider.

This pretty much mirrors my experiences, although I can't vouch for the actual numbers.
In actual riding, most people increase their power output going into the wind or up a hill and let up on the downhill, but the amount that they do so varies considerably.
In the headwind case, the logical thing is for Mr Lite to duck in behind Mr Heavy, and it may be fastest for the team for Mr Heavy to pull the entire way.

For the uphill case, Mr Heavy can make up a small part of the extra time on the downhills.

Theoretically, I suppose you could have heavier and lighter riders with exactly the same power output per pound, but there aren't too many riders that get much past 200 lbs without carrying some extra flab. Then also, you may have less heart/lung capacity per pound of body weight with larger people, that would explain why football linemen aren't out winning the marathons.

Originally Posted by Kontact

But output on flats is power, and larger people have more power.

Originally Posted by HTupolev

Performance on the flats is power versus aero profile, not just power by itself.


It seems to me that a vacuum would just eliminate the power-to-aero advantage that the larger people have, and it would become just about entirely a power-to-weight game. For anything other than a sprint event (where the aerobic-capacity-to-weight thing isn't so much of a problem), the bigger folks would lose their benefits on the flats and they'd still be screwed on the climbs.

Originally Posted by Kontact

On flats, power to weight is meaningless. It's flat.

Originally Posted by HTupolev

It still affects acceleration. Rolling resistance is complicated. But yeah, I'm not saying that the smaller people would crush the bigger ones on the flats; I'm saying it's not obvious that they'd be disadvantaged on the flats, and they'd retain their climbing advantages.

Originally Posted by Kontact

In a motor pacing environment, a 200 watt rider would crush a 100 watt rider, regardless of weight.

Originally Posted by HTupolev

It doesn't make any physical sense to say that power is the only consideration. What resistance is the power being used to overcome? It's always something.

A 100W cyclist with 100lb bike+rider system can accelerate just as quickly as a 200W cyclist with 200lb bike+rider system. Rolling resistance also tends to increase with load; as I said this is more complicated, but it's not a trivial thing that can simply be ignored.
It's true that reduction of air resistance through drafting is a considerable part of why tiny riders can keep up with bigger ones on the flats. But air resistance - and in particular the smaller rider's aerodynamic profile having been larger relative to their power, due to the latter often scaling faster with linear size than the former - is also the main reason that they might have been slower in the first place.

Originally Posted by Kontact

power minus rolling and bearing drag will predict top speed.

Originally Posted by HTupolev

Power divided by rolling and bearing drag will predict top speed. When you're at the top speed, the power of the rider is equal to the power lose to those drags. If this weren't the case, the system would be accelerating.

If you're delivering 200W to your rear wheel in a vacuum at a steady cruise, you'd be going insanely fast and you'd have nearly 200W of rolling resistance with the rest being taken up by bearing drag.


In my experience it's frequently the opposite. Bigger riders frequently have very good 20-second power to weight, it's over longer efforts when their poorer cardio-to-weight catches up that they have a problem. I know plenty of clydes who can fly away from me up quick rises, but who I totally destroy on long ascents.