How to determine the minimum tire pressure if the manufacturer does not?

Question

Some tires only have the maximum pressure written on them, stating nothing about the minimum. For soft and comfortable rides, the recommendation is to inflate them to lower pressures, but then how to avoid under-inflation? Should we just not overthink it and stick to a reasonable value, such as 80% of the maximum pressure? (That's what I would estimate based on a few pressure charts I have seen.)

Batman · Accepted Answer

Smaller tires need to be run at higher pressures to accommodate the same weight. You want to have enough air that the tire's rolling resistance is good but you don't get pinch flats / damage from appropriate road hazards. Too little/much air can affect control to some extent as well. If you have tubeless tires, you can usually run lower pressures (since there is no tube to pinch flat); your rims may or may not be setup for this.
If the tire isn't deflecting, the tire is overinflated. You should see some (but not a huge) amount of deflection when the tire is loaded. Here are some pictures from Schwalbe:

I'd start with some guide like this one from Schwalbe as a guideline (interpolate/extrapolate for your body weight/tire size, and move up / down if it seems over/under inflated)

Tire Width
Body Weight

130 lbs (59 kg)
185 lbs (83 kg)
240 lbs (109 kg)

25 mm
85 psi
100 psi
115 psi

28 mm
80 psi
95 psi
110 psi

32 mm
65 psi
80 psi
95 psi

37 mm
55 psi
70 psi
80 psi

40 mm
50 psi
65 psi
80 psi

47 mm
45 psi
55 psi
70 psi

50 mm
35 psi
55 psi
70 psi

55 mm
30 psi
45 psi
55 psi

60 mm
30 psi
45 psi
55 psi

80% of the sidewall pressure may be too high/low for you; it depends on how heavy you are and what that manufacturer put on the sidewall. However, once you pump up your tires a few times and get a feeling for what tire pressures work for you for your tire sizes, you won't really worry and will have a natural feel for it.

How to determine the minimum tire pressure if the manufacturer does not?

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Tire Width	Body Weight
	130 lbs (59 kg)	185 lbs (83 kg)	240 lbs (109 kg)
25 mm	85 psi	100 psi	115 psi
28 mm	80 psi	95 psi	110 psi
32 mm	65 psi	80 psi	95 psi
37 mm	55 psi	70 psi	80 psi
40 mm	50 psi	65 psi	80 psi
47 mm	45 psi	55 psi	70 psi
50 mm	35 psi	55 psi	70 psi
55 mm	30 psi	45 psi	55 psi
60 mm	30 psi	45 psi	55 psi