I was thinking in recent days about the power consumption involved in cycling. I knew from experience that speed costs energy, but how much I didn't know. I went looking for an online cycling calculator and found http://bikecalculator.com/. I inputted my weight 154 pounds and my loaded touring bike (bike and cargo) at 55 pounds and started to play around with different speeds, on level ground. As I suspected power consumption increased rapidly with speed.
A brisk walking speed is about 4 mph, at this speed it takes about 10 watts to keep me and my touring bicycle moving. At six mph energy consumption jumps to 18 watts. Eight mph needs 35 watts. Ten mph will burn 43 watts and after this power consumption increases rapidly. Twelve mph will need 64 watts. At fourteen mph it takes 90 watts. Sixteen mph needs 124 watts and twenty mph requires 217 watts.
It takes five times more energy to move a bike at 20 mph than it does at 10 mph. The modest jump in speed from 10 mph to 14 mph doubles the energy used.
When I go cycle touring my aim is to maintain an average speed of around 10 mph, as I can keep going for many hours at this speed. The longest I've yet cycled is 146 miles in a day, to do this I spent nearly 15 hours out of 18 on the bike. At the end I was mildly tired rather than exhausted.
I also tested out the impact of weight on power consumption. My Carrera TDF road bike weighs 26 pounds, to move it at 10 mph takes 40 watts, a saving of only three watts over a 55 pound loaded touring bike. At 20 mph it takes 210 watts to move the road bike a saving of only 7 watts on the touring bike. On flat ground there is very little difference in the energy needed to move a loaded touring bike and a light road bike.
Even a very heavily loaded touring bike will not take much more energy than a light road bike. The heaviest weight I ever carried (bike and cargo) is 79 pounds, to move this at 10 mph only needs an extra 6 watts over a light road bike.
Weight does however tell when climbing hills. Climbing a 5 % gradient at 4 mph on touring bike will burn 109 watts. The same slope can be climbed at the same speed on a road bike for 84 watts.
The question of power consumption is a bit more complex than this, it fails to take account of things like rolling resistance of different tyres, and how well serviced a bike is. But it is a good rough guide to the kind of power consumption involved in cycling.
