Originally Posted by
JohnJ80
How does that vary with rider weight/size?
J.
Not as much as you'd expect.
Think about riders going the same speed.
Consider an extra 100 pounds which is 45 kilograms and ignore the aerodynamics.
I measured 923kj on my last fast flat 41.8 km ride (26 miles).
Multiplying 41,800 meters by 45 kg, 9.8 meters/second^2 gravity to get force normal in Newtons, and .005 for a high coefficient of rolling resistance yields 92,169 joules. That's about 92 Calories at typical cycling metabolic efficiency, or 10%.
I measured 1932kj on my 104km metric century (65 miles) with 720 meters of climbing (about 2360 feet).
Multiplying 720 meters by 45kg and 9.8 meters/second^2 gravity yields 317,520 joules which is about 318 Calories. Add 229 for rolling resistance and you're up to 547 for a 28% increase.
For a 50 pound weight difference you'd only have 5 and 14% differences.
Aerodynamics are less related to weight. Many of us are or were Clydestales due to fat which doesn't appreciably change our surface area and therefore aerodynamic drag in the same position. At my largest I was 215 pounds; in peak cycling form 138. Same height, shoulder width, and approximate drag either way.
Where they come from size there usually isn't too much variation. The average American female is about 5'5" versus 5'10" for the average man. Assuming the same proportions that's only a 16% difference in surface area and drag.
Offset that by average women having less power than average men and more larger people being in poorer shape so the speeds are lower, aerodynamic drag lower, and Calories per mile lower.