3 ms·

There is some research into how much energy is lost to suspension style losses, and it's on the order of 100W (was 300) when riding at 20mph/30kph over rumble s

There is some research into how much energy is lost to suspension style losses, and it's on the order of 100W (was 300) when riding at 20mph/30kph over rumble strips. (https://www.renehersecycles.com/myth-17-bigger-wheels-roll-faster-amended/ https://www.renehersecycles.com/myth-17-bigger-wheels-roll-f...). This can be changed pretty dramatically with good tires and proper inflation. On more reasonable road surfaces, it's less than 1/10th of that number. (but good tires make ooooh so much of a difference. I don't notice bad chipseal. My clubmates -- not so much) (edit sorry -- rereading the article, I misread the graph. 300W on the rumble strips ~200 on the smooth pavement beside them)

franciscop 6y ago
Thanks for linking the article! It seems to say that 300W is the energy needed on the rough terrain, not the energy consumed by the bumps: "We measured the power required to pedal the bike at 32.2 km/h (20 mph) using an SRM crank." Then it goes on to measure the energy required on the smooth pavement and it's around 230W. So around 70W of INPUT energy is needed because of the strips. Now if speed is constant, it stands that a part of these 70W are converted to vertical motion (the rest lost to heat in many forms). This is where I don't dare to understand thermodynamics enough to even make an (un)educated guess of how little of those 70W are converted to vertical motion.
- wiredfool 6y ago
  Yes, I edited that when I reread the article. The conclusion drawn from the article is that the 70+W is vibration of the bike that is damped (lost) in the rider's body. Adding suspension by running supple tires at lower pressure reduces the energy required to go over the rumble strips (https://www.renehersecycles.com/myth-16-higher-tire-pressure-is-faster/ https://www.renehersecycles.com/myth-16-higher-tire-pressure...). That one compares 26mm tires at 75 vs 95 psi, but there's a page somewhere that I think shows wider (think 42mm+ tires) at more like 25psi.

franciscop 6y ago

Thanks for linking the article! It seems to say that 300W is the energy needed on the rough terrain, not the energy consumed by the bumps: "We measured the power required to pedal the bike at 32.2 km/h (20 mph) using an SRM crank." Then it goes on to measure the energy required on the smooth pavement and it's around 230W. So around 70W of INPUT energy is needed because of the strips. Now if speed is constant, it stands that a part of these 70W are converted to vertical motion (the rest lost to heat in many forms). This is where I don't dare to understand thermodynamics enough to even make an (un)educated guess of how little of those 70W are converted to vertical motion.

wiredfool 6y ago
Yes, I edited that when I reread the article. The conclusion drawn from the article is that the 70+W is vibration of the bike that is damped (lost) in the rider's body. Adding suspension by running supple tires at lower pressure reduces the energy required to go over the rumble strips (https://www.renehersecycles.com/myth-16-higher-tire-pressure-is-faster/ https://www.renehersecycles.com/myth-16-higher-tire-pressure...). That one compares 26mm tires at 75 vs 95 psi, but there's a page somewhere that I think shows wider (think 42mm+ tires) at more like 25psi.