Staying on this tangent..
Originally Posted by
brianogilvie
This is a little off the main topic, but since it came up:
Jan Heine and Mark Vande Kamp measured the real-world performance of various tires, and they determined that a wider tire (28-30mm on 700C rims) with a supple casing, run at moderate pressure, was more efficient than narrower tires run at high pressure. The higher rolling resistance of the wider tires was more than balanced out by the lower suspension losses from road irregularities. See Jan Heine and Mark Vande Kamp, "The Performance of Tires," Bicycle Quarterly vol. 5, no. 1 (2006), p. 1. (Not available online, unfortunately.)
If it's related, I can keep pedaling harder and longer if I'm on a smooth road -- or, if the surface is a little rough, I'm on a bike with suspension.
If I'm on my road bike and am on a rough, crappy, washboard section, or maybe a wooden bridge, I'm spending more effort just to absorb the shocks with my body. I don't get the chance to sit there and pedal. But, if I'm on my FS MTB, I can barrel down a limestone trail, chattering washboard and ruts and all, pounding away on the pedals nonstop.
Back on the road bike -- I think there's a balance between distruptively-bouncy-hard and energy-sapping-soft with tire pressures. If I use the recommended pressure from that BQ article or the pressure from psimet's formula, it works pretty well. I would consider lower pressure for rougher conditions, but then I'd be more worried about pinch flats and rim damage -- which means that I'd rather use bigger tires instead.