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