I'd like to see better science. There are only two data points above 120 psi in the graph presented in http://www.slowtwitch.com/Tech/What_s_i ... _1034.html
" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; referenced above, and it implies that 130 psi has the same Crr as 75 psi (and ~150 = 60). I don't believe it. Two data points measured with a PowerTap do not make a statistical conclusion. Even so, the delta Crr in the graph between 115 and 130 psi is about .001. If somebody farted in front of him it would have skewed the results more than that.
Is there a better scientific study on this? I fully agree there is a sweet spot. 130 psi on Vittoria CX clinchers felt "bouncy" on certain stretches of chip & seal, and I could feel it was inefficient, but that versus the entire ride at 75 psi and I would think 130 would still prevail.
I could probably help you with that, especially since I took that data and wrote the article
If you read the article carefully, you'll see that what is actually measured in a field test like that is NOT the tire's Crr, but the entire "bike + rider" system's "resistance to forward motion". That's a subtle difference. Although the tire's inherent Crr is reducing with increasing pressure, at some point the tire basically becomes so "stiff" that it starts transmitting undue amounts of vibrational energy THROUGH the tire (instead of being absorbed by the "air spring" of the tire and mostly returned to the road surface) where it is dissippated in the rider's "squishy bits" <to use a technical term>
THAT'S why (for a particular tire, rider weight, pressure, and speed) there's a "breakpoint" pressure above which the resistance to forward motion (i.e. the thing we REALLY care about) starts increasing...and apparently dramatically so.
People seem to forget that the pneumatic tire is the MAJOR source of suspension on a road bike. Don't "lock out" that suspension by pumping your tires up too high.
BTW, those data points are the result of literally hundreds to thousands of individual power readings taken during the course of a field test run
Oh...and a delta Crr of .001 is ~equivalent to a 10W difference in power at TT race speeds. That's a strong
Here's the funny thing I remember about that test...if I had to choose what felt
faster in a blind test, I'd pick the highest pressures. But, that just shows you how fallible human perceptions can be. Luckily, the stopwatch and power meter don't lie