On Fri, 15 Dec 2017 16:07:29 -0800 (PST), HaloTupolev
wrote:
but don't say anything about width-vs-speed penalties.

Compass generally claims that width itself doesn't cause significant
differences in net performance.

I can't remember which issue it was (43 maybe?), but one of the
editions of Bicycle Quarterly included testing on the apron of
Marymoor Velodrome where the entire range of Compass tire widths
performed identically, within the precision of their measurement
methodology.

I haven't read that one, but their earlier ones involved roll-down
testing and (from one of the photos in the article) timing with a
wris****ch. I put little credence into that article because if the
likelihood of noise in the data.

They later did some interesting testing using a power meter, which
struck me as a better way to assess performance.

That said, I think that Compass is correct in that given identical
construction (casing, tread thickness, rubber compound) the effects of
width as a variable would be small. The more traditional drum tests
suggested (e.g. the ones done for Avocet). For as long as I can
remember, most wider tires also feature heavier casings and much thicker
rubber- wide high performance tires were rare. Compass has pushed in
that direction quite aggressively and good for them.

Compass's assertion that inflation pressure has little impact on
performance is out of keeping with that testing, although when
real-world road textures/roughness are included there may be relatively
little adverse impact from lower pressures. Jim Papadopoulos wrote
about that in this forum many years ago under the rubric of suspension
losses, and his thinking had a direct impact on Compass's tire design
philosophy.

My bike with 26 x 1.8 Compass tires seems as fast as my bikes with 700 x
25 or 700 x 28 Paselas. At least based on average speeds on my cycle
computer and similar subjective effort. That is of course far from a
scientific approach!