Bicycles Asked on May 10, 2021
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 "ball-park" 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.
Correct answer by Andy P on May 10, 2021
AndyP is right - the scaling is far from linear with weight. Anyway your reading has a fairly large margin for error.
But you can approximate your calorie burn by calculations (which is likely to be less inaccurate than a cyclocomputer if that doesn't take into account ascent, e.g. if solely wheel-driven). Even so the surface is important and is ignored by anything I can find. If you're on road or very smooth gravel, this will be good enough.
Easy option: upload to a fitness website
You could upload to route to Strava (free, but you have to register) for your weight, and then change the weight to get the values for other riders (you need to delete the ride, change the weight, and re-upload for it to update). I believe Komoot and RideWithGPS will also give you this information but I use those only for planning. This is what I would do, and the estimates are OK for casual riding, touring etc.
Tedious estimation option
You can estimate without Strava though. I'll assume a perfectly flat ride for now, then discuss how to account for a bit of climbing.
Using bikecalculator.com you can plug in your weight, riding position, tyres, etc. and the details of the ride. You'll get a number out for calories burn that will hopefully bear some resemblance to what your computer says. Then you can change the rider and bike weights to estimate for other people. If you choose, you can use these to scale your recorded figure, but I'd only do that if using a bike computer with altitude (ideally barometric; GPS altitude is poor in many conditions).
If the ride isn't completely flat, break it down into sections that are consistent within themselves:
Bikecalculator's metric trip calculator allows up to 6 segments with different speeds/gradients and the same rider/bike information. Note that it's not clear whether the calculator takes into account a difference in frontal area for smaller (lighter) riders; I would assume not.
Another easy option for the future Use a mobile phone bike computer app for each rider. Plenty don't need a data connection and will run on old phones (e.g. relegated to kids' use). Giving the same details to an app and your computer will also give an idea of the spread in the estimates.
Gold standard Buy a power meter for every bike, along with a suitable head unit (or phone app), again per bike. Stupidly expensive and unnecessary even for many of us who ride quite seriously (but don't race), let alone for a family ride.
Answered by Chris H on May 10, 2021
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