On 29 Jun 2006 12:02:23 -0700, "SYJ" wrote:

Do bumpy road surfaces typically exact costs in riding efficiency?
While doing a loop that I've ridden dozens of times, I noticed that my
speed had dropped almost two MPH from my norm on a section that had
recently been chip sealed (as opposed to the baby's butt smooth
pavement that existed previously). I didn't feel especially cooked (at
least, no more than usual), there didn't seem to be any wind, and I was
able to ramp the speed back up to normal after turning off the choppy
surface, all of which led me to question whether it was indeed the
bumpiness that was affecting me.

Does anyone have any similar anecdotes? Any studies of this? Was I
dreaming? I'm curious if it is more beneficial in a long ride/race
where crappy roads are the norm to use 25mm tires vs. 23s.

TIA,

SYJ

Dear SYJ,

Yes, rougher surfaces slow tires down.

Coefficient of Rolling Resistance
Wooden Track 0.001
Smooth Concrete 0.002
Asphalt Road 0.004
Rough but Paved Road 0.008

http://www.analyticcycling.com/ForcesSpeed_Page.html

If you plug those values into the calculator and use the defaults, you
get speeds of 7.79, 7.68, 7.46, and 7.04 m/s, or 17.43, 17.18, 16.69,
and 15.75 mph.

The effect of chip seal is quite noticeable. My daily downhill speed
improved nicely years ago after the wretched chip seal was paved.

Cheers,

Carl Fogel