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

Do bumpy road surfaces typically exact costs in riding efficiency?

Yes, particularly if the bike has high-pressure tires and lacks
suspension.

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.

It was the road. There may have been an additional penalty from the
stickiness of the surface if the sealer was leaking through to the top
of the gravel layer, but a good tar-and-gravel application won't put
any tar on the top.

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.

2mm of tire won't help IMO. 15mm might, but I would expect the gain
to be small if any. I can't offer any figures to support that
assertion; it's just an opinion based on limited experience. I know
that swapping from a knobby to a smooth tire of the same size had a
benefit similar to what you saw in the case of the smooth vs
gravel-encrusted surface. Wider tires may produce increased rolling
resistance relative to a narrower one (partially due to running at a
lower pressure), and they add to the frontal profile (and thereby to
drag) somewhat as well.
--
Typoes are a feature, not a bug.
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