How does one extrapolate riding calories to fellow riders? A 30-kg child, a 60-kg adult, and a 90-kg adult go on a bike ride.
The 60-kg adult uses a cyclocomputer, which knows the weight of the adult—and gender and age, as well as the weight of the bike.
At the end of a ride, the cyclocomputer declares that the trip used 1000 calories.
Would it be accurate for the 60-kg adult to declare to the child and to the other adult that—if we were to ignore gender + age differences, as well as the difference in bike weights, which may well be serious omissions—that the child has just spent roughly 500 calories and the adult 1500 calories?
Two cyclocomputers may not even agree on the estimation of calories, and so this question only seeks a very rough &quot;ball-park&quot; confirmation whether the relation is linear.
In short, do cycling calories scale near-linearly with weight?
Since older children are typically quoted as needing 1500 calories per day, compared to an adult's 2000, before factoring in exercise, might we use this to expect that a child is using 75% of the calories during exercise as well?
No, calorie burn does not scale linearly and can vary based on a great many factors.
Calorie consumption is very closely tied to power output.  Power in watts x4 is usually considered a good estimate.
If the entire ride was on a steep climb using tyres with virtually no rolling resistance, then in this case you would be correct.  However on a real ride other factors come into play (rolling resistance and aerodynamic drag).
In terms of rolling resistance, there is a large variance between tyres - or even between the same tyres at a different pressure.  This will also change (but not linearly) with rider weight.
Increases in body mass also do not lead to a linear increase in aerodynamic drag.  Further to this, power output can change a lot due to a riders position and clothing.