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I read lots of education around how the high pressure for a MTB tire is bad and how the low pressure is very good for the rolling resistance. I feel puzzled by these talks because they seem contradicting my experience. From the other side, I have not done any precise measurements.

Has anybody actually measured the rolling resistance as a function of tire pressure, using a MTB-like tire (so wider than 2" or about) and the MTB pressure range (somewhat between 1.8 till 4.0 bar I think), I mean experimentally? Would it be possible to see such a table or chart? It would be interesting to know if these low pressure recommendations are some contra-intuitive reality or just an urban legend, pushed by desire to sell easier generally good (soft maybe) but not pressure-tolerant tires as "high end". I understand that low pressure likely results more grip and may be better on something like sand. This question is about the rolling resistance on a reasonably hard surface, however.

There is a good chart here but it starts at 4.1 bar. This is already more than a typical MTB tire is designed to hold so does not look usable for my case. It declines till 7 bar is reached that looks for me above the extreme, only then starts growing again.

Simply "manufacturer recommendations" are out of scope of this question, unless they do provide the measurement data covering the relatively wide range.

nightrider
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    Low pressure is more about ride qualities, grip and so on. There is this concept of impedance and the effect on the rolling resistance https://silca.cc/blogs/silca/part-4b-rolling-resistance-and-impedance but I doubt you will find realistic data on realistic terain for MTB. Even for racers the best pressure is often a compromise, they do not go only for the lowest rolling resistance. In a difficult terrain a low pressure helps to stay upright. – Vladimir F Героям слава Mar 30 '22 at 16:04
  • No data then no data. – nightrider Mar 30 '22 at 16:10
  • The experimental data I've seen are specific to a particular course and trail surface. Maier et al (https://pubmed.ncbi.nlm.nih.gov/28282753/) estimated rolling resistance for MTB tires prior to the 2016 and 2020 Olympics (with good results) with varying pressure and rim width, but those were for a specific set of races by a particular rider so I don't think a general table would be very useful. They did validate the measurement method, however so if you had the time and equipment you could do the tests yourself. – R. Chung Mar 30 '22 at 16:23

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This website provides rolling resistances of MTB tires on hard surfaces. It confirms your observations: lower pressure = more resistance.

I don't remember having read that lower pressure = less resistance. What I commonly read though is that wider tires have less rolling resistance at equal pressure. So you can inflate them less for the same resistance, which is a benefit for comfort/grip.

Another point is that low pressure can also be faster on irregular terrain, since a tire with a high pressure will bounce: horizontal momentum will be converted into vertical movement. But "faster" does not imply that the rolling resistance is lower: in that case, other effects are impacting the speed.

Rеnаud
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    This website tries to compare all tyres on an equal footing by using the same rig and methodology. That's fine, but does discount the use-case where an off-road tyre at 20 PSI needs grip more than it needs low rolling resistance. So, compare the results in the class, or between several similar tyres, and don't try to directly compare the resistance of a GP5000 with a 4" fat bike tyre. – Criggie Mar 30 '22 at 20:44