Tire pressure for fastest speed has been a hot topic in the roadie world for the past few years. It turns out there is an optimum pressure that depends on the road surface roughness (as well as tire and rim size, and rider weight), and it is usually lower than most people think (at least for road/gravel riding).
At too low pressure, you lose power deforming the tire as it rolls, and at too high pressure you lose power by lifting the bike and rider up and over all the little bumps instead of absorbing them in the tire (assuming we're talking about non-suspension bikes here). The rougher the surface, the lower the pressure you want for max speed.
Most people equate the road feedback they feel with high pressure tires to speed, but if you can feel every little bump in the road you're actually wasting power with all that vibration. Plus, if you're hanging on for dear life to stay in control, you're probably not pedaling as hard as you could.
This chart is a good starting point for pressure vs rim size, tire width, rider weight, and surface type. I don't know if these pressures are optimized for speed or something else, but I just got my best Strava segment result ever (2nd place!) on a gravel path following their gravel pressure recommendation.
https://www.enve.com/en/tirepressure/
Depending on your riding goals, you may want to adjust your pressure for something other than max speed (e.g. lower pressures for traction and a more comfortable ride, or higher to prevent rim strikes or pinch flats).
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