A supple casing allows the tire to more easily deflect and therefore compared to a stiffer casing at the same tire pressure it will ride smoother and when it does deflect it wastes less energy because it's more receptive to being moved the amount that it did.
Higher tire pressure reduces the amount the casing will deflect and therefore reduces movement in the casing and thus reduces that form of casing related energy loss. Then at some variable point the roughness of the surface will dictate when too much pressure is being used - the bike is tossed about, more difficult to control, traction is compromised, and it's a pain to ride. Velodrome tracks don't have rough surfaces so it's a perfect place to capitalize on ultra high/ultra efficient tire pressure. Cyclocross is the opposite - you need that softening of the ride that lower pressure brings otherwise traction, handling, and comfort suffer.
But bottom line, lower air pressure is not lower crr with respect to the tire. Case in point is a tire at 20 psi - very, very sluggish. But in the correct range, lower air pressure could offer an increased efficiency in terms of traction, handling, comfort, but still will never be a winner in the crr arena.
Al Morrisons' tire testing has several tests with those garden hose Tufo's. He does it at various pressures. It aligns with the recent velo news test. That lower pressure might ride nicer but it brings with it higher crr.
http://www.biketechreview.com/tires_old ... g_rev9.pdf" onclick="window.open(this.href);return false; go to page 4 at the bottom.
My understanding the wider vs narrow tire is that a wider tire can be run at a slightly reduced pressure than the narrow for the same security of knowing that it is properly supporting the weight of the rider. Think for instance if you had a tubular tire the size of the truck tire that is pumped to 120 psi. When you get on that bike the tire will deflect almost zero compared to sitting on a bike with tires that are 5mm wide at the same pressure. So you have a "safe-to-operate" range for each size of tire. The lower pressure brings with it a bit more comfort. At the lower pressure you generally will see some added crr to some extent compared to a narrower tire at it's slightly higher pressure. So if you pump that wider tire to the same psi as the narrow tire (like they do in those roller tests) then you have less casing deflection on the wider tire and it will win the crr battle......but the ride should be (very) slightly more "rough" than the narrow tire. So it's horses for courses. Are you heavyweight or someone who rides rough roads who needs a tire to not bottom out and be comfortable - go wide. Are you a lighter build and good roads + aero does come into play - then the traditional 21/22 mm casing is still a winner. What you are seeing the wheel folks then doing is selling wide rims to fit well with wide tires so the profiles of each stay fairly even....and there are a lot of heavy people spending cash on go fast bikes these days....
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