Originally Posted by
cyccommute
Lowering the pressure increases the rolling resistance. Using a wider tire reduces rolling resistance over a narrow tire but not if you lower pressure at the same time.
There is also a practical limit to lowering the pressure and, in my opinion, most people are below that limit. A tubed tire will pinch flat if the tire pressure is too low. What many people don’t understand is that pinch flat is telling you something. The tube is pinched when the tire is trapping the tube between the tire and the rim. You are risking impacting the rim on the ground and the result could be a damage rim. Damaged tubes are fairly cheap to fix. Damaged rims are far more involved and far more expensive.
.
Yes, there is a lower limit... and the larger the tire, the lower that limit is. Thus, as a I said, the larger tire alows lower pressure.
As far as rolling resistance.... Sure, if you drop it too much you will have more resistance. But if - as you say - the larger tire rolls faster at the same pressures, then you can drop the pressure until the RR is the same.
Out of curiosity, do you run the same pressure in a set of 25s and a set of 38s?