Originally Posted by
PeteHski
Calculators like Silca and SRAM all clearly state that they are intended as a starting point from which to fine tune your setup as required. But I haven't yet found any reason to deviate from their recommendations. If they didn't exist I think I would end up running pressures too high, especially with wider road tyres. The drop in pressure with increasing rim and tyre width is surprisingly high. More than most people would probably guess.
I am not sensitive enough to feel subtle differences, nor do I ride so consistently that marginal gains in speed will manifest themselves, so I just go with a pressure in the ballpark of their recommendations.
OTOH, last week I wanted to try 32mm tires, but I didn't want to pay $50-$80/tire to get 32mm GP5Ks to replace the 28mm GP5Ks on that bike, so instead I got 32mm Vittoria Corsa G2.0s, because Bike Closet has them for $35 each. I swapped them in, pumped them up to 70/75 (roughly Silca's recommendation) and went for my usual Sunday 59 mile ride. They were comfy, yes. Not necessarily that much comfier than the 28s at 80/85. But they were definitely SLOWER. I ended up with about 0.4 mph slower average speed over that route than my all time average for it.
Then I looked up the rolling resistance for GP5Ks and Corsa G2s on bicyclerollingresistance.com, and the Corsas have a 4w disadvantage. So I went to Bike Calculator and played with the power, and sure enough, that 8w disadvantage (2 tires) yields 0.4 mph slower speed.
So, in the end, I executed a poorly controlled experiment and learned nothing.
