I ride a 2006 Rans Stratus XP with dual 26" Velocity wheels and
Schwalbe 559-28 (26" x 1.1") tires. I also have a set of the same
Velocity wheels (same rims and hubs, but fewer spokes) in the 650
size from my Bachetta that have Continental Ultra Gatorskins 571-23
(650 x 23 cm) on them.

I was curious if the 650 wheels with their thinner tires might have
less rolling resistance than my 26-inchers. So I roll-tested both
sets of wheels/tires. There is a hill near my home with a relatively
steep initial slope and then levels off to a steady shallow slope. I
started each run from a dead stop, accelerating by gravity alone. I
noted the time elapsed at the bottom of the hill, 1.05 miles from
the start. I did 3 runs with each wheel/tire combo. Top speed was
23.0 to 23.5 mph and the runs ended at around 12 mph.

The only variable I could not control was wind. I had a very slight
tail wind of about 3 mph - and it seemed fairly consistent - perhaps
a little more tail wind with the 650 runs - there were a few flags
with some movement, but when I tested with the 26" wheels, the flags
were completely limp - so I may have had a tad more tailwind during
the 650 tests.

Below are the tabulated results:

571-23
Distance Seconds Ave.Spd.
1.05 254 14.88
1.05 253 14.94
1.05 246 15.37
1.05 251 15.06 Average

559 - 28
Distance Seconds Ave.Spd.
1.05 243 15.56
1.05 258 14.65
1.05 251 15.06
1.05 251 15.08 Average

If these numbers are to be believed as meaningful, it would seem the
two sets of wheels/tires have approximately the same rolling
resistance. Both types of tires were pumped up to between 120 and
125 psi. Perhaps it is true what they say about fatter tires at the
same pressure have lower rolling resistance than thinner ones.

The wider tires have a noticeable smoother ride. I think I'll be
keeping the 559s on rather than going to the 650s.

Hope this is of interest to someone.

Terry Farrell
Tampa, Florida
80 degrees & sunny today!