Back on topic…Here’s the original question posted by @Bullseye.
Yes, power does not scale linearly with athlete mass, leaving the larger riders out the the back.
This is an interesting video about the 150 year history of rowing which touches on the subject:
VO2max increases at a rate of Mass^0.75
Mike
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Yes, I know!! The original question was answered very early on in the thread, which then got derailed by some folk suggesting that a heavier rider will climb faster at the same w/kg. I don’t agree with that point of view and was trying to illustrate it with real world examples, not numbers thrown into a speed calculator.
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In an elite road race their rarely racing in the context of a single effort. They have to manage their effort in the context of a stage race or a season. Yes, they have the ability to dig an incredibly deep hole with their fitness, but they have both short and long term obligations that keep them from going that deep. Playing the kJ game matters a ton in pro cycling.
I just stumbled on this video from Road.cc:
Here they take two riders, one light, one heavier and, instead of trying to hold the same W/kg, they ride side by side (so at the same speed) and see if their resulting w/kg is the same. Spoiler alert: it is not 
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Excellent find!
This is also why drafting is still important when climbing. You often hear commentators say rider such and such is being pulled up the mountain by their team mate.
Even if the rider is only saving 5% power by drafting, that is meaningful when they are on the edge of their ability.
jakchylinski’s post gives a good answer.
When we are dealing with a measure of cycling performance expressed as a physics equation (ftp in W/Kg), there is no need to make random guesses based on intuition. This is a pretty strictly numerical question.
Jak helpfully distinguishes resistances that the riders will face going uphill.
Here is how you break them down:
- Gravity: Assuming total weight of the two riders, with bike and kit included, is factored into the calculation of their ftp, neither one has an advantage. This is because as weight increases, the force required to counter gravity increases LINEARLY.
(This is assuming a constant speed, but acceleration would favor the lighter rider, and deceleration the heavier. because of intertia)
Since ftp is calculated without equipment and bike, even if gravity is the only consideration, when fully kitted, the heavier rider will ascend faster: 375watts/75Kg + 10Kg kit= 4.41W/Kg but 250Watts/50Kg + 9Kg kit= 4.23W/Kg
Advantage: Heavier rider
- Air resistance. This is a bit trickier. Drag increases proportional to area facing the direction of motion (assuming no variance in turbulence per size and speed). So if the heavier rider has a proportionally larger area facing forward, his increased drag would be directly counter-acted by his increased power. Again this is a linear progression.
Since humans increase in weight at a higher rate than they increase in frontal surface area, the heavier rider is probably not proportionally larger in drag, so this is again an advantage to the heavier rider.
We can also note that the effect of drag will decrease on both riders as they climb, since speed will drop. This makes gravity and rolling resistance more significant comparatively as the incline increases.
Advantage: Heavier rider
- Rolling resistance: This is the most complicated (I think). On the same tire, with the same pressure, rolling resistance will increase more than proportionally for the heavier rider (e.g. about 20% increase in weight might cause ~24% increase in resistance). However, increasing the tire pressure for the larger rider probably means less of a penalty for the added weight (more in the range of 16% increase in resistance for 20% added weight).
The heavier rider seems to have at least once clear disadvantage: As the angle between forward momentum and the road surface increases, rolling resistance will increase at a rate more than proportional to the weight of the rider+kit. Additionally, because power output to the tires is not smooth, as inertia becomes less of a factor, the rider’s pedaling power is expressed increasingly as torque (I think), making rolling resistance increase at a much faster rate than weight.
Advantage: Lighter rider
I don’t think the described increase in rolling resistance is significant compared to the gravitational and (reduced) drag advantages that the larger rider has. Thus calculators should give the advantage to the heavier rider.
I knew my liberal arts education would be good for something…
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You do also have to note that they had almost identical power to weight ratios on the steeper bits and below 4-5% they did drift apart quite a bit. So when you are riding on steeper 7-8% + gradients having the same power to weight you should climb at the same speed. Then when you are on the shallower gradients absolute power starts to matter much more because of aerodynamics.
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