I was long skeptical of the "lower is better" line. Why? Because of literally hundreds of hours of road-testing different models of Mtb tires at different pressures over several years. I tested them on roads much rougher than any roady or triahtlete will ever see. Here's one of the smoother parts.




The results of this testing were very consistent: higher pressures were better. This lead me to ride (and win) the Mt. Ashland Hill Climb race several years running with Mtb tires inflated around 80psi.

So how do we resolve that with Tom & company's tests? You'll note that the bikeradar guy, like me, tested up a steep grade. I have speculated that, at low speeds up steep grades, the big torque from the rear wheel stretches the tire in a circular fashion. If you watch a low pressure Mtb rear tire as you go up a hill, you can actually see the ripples in the tire indicating this. So in addition to the normal hysteresis loss that we think of, you have a sort of torsional loss.

Some day, I'll redo these tests on both the hill and the flat ground. My suspicion is that the lower pressures will do much better on the flat than on the hill.

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