Tyre pressures, Resistance and Rollers
Lead Photo by Teocalli
With the current trend to wider tyres and tubeless there is also a trend to running lower pressures. The manufactures and the science says that there is no net loss in speed and/or efficiency in running lower pressures and some claim it may be faster. Well, I guess I have to believe the testing behind all that.
Unless you are on Rollers.
Over the winter I was doing a Roller session and started to get rather worried as the whole thing was getting harder and harder to maintain anything like my normal speed. Given my recent history I was getting quite worried until I noticed that I had a slow rear puncture! I must have had a small stone sliver in the tyre at the start and the greater point pressure of the rollers had caused it to puncture, though at a slow rate.
Having noticed this I pumped back to 100 psi and found I was back up to speed, for a while, till the tyre started to deflate again. It had got down to 60 psi and at that pressure it was like being on a pretty decent incline.
Anyway, this week I had cause to think on this when I was doing a roller session due to rain (and being a whimp). I pulled a bike from the rack and did not check tyre pressures but found I was down on comfortable max cruise speed by 2-3 mph. On checking pressure I was at about 80 psi. Pumping to 100 psi and I was back up to a healthy speed (for me).
So, my conclusion is that starting from 100 psi on 25mm tyres I’m losing about 1 to 1.5 mph for every 10 psi pressure loss. I don’t run a power meter so I can’t do any empirical measurement but it might be interesting to run a test as pressure is lowered and see what power increment is required to maintain speed.
It does make me wonder how the manufacturers take their measurements of rolling resistance.
Anyway, if you are on Rollers and want to run a resistance session the cheapest solution may be to just lower your tyre pressure!