Test both front and rear wheels.

I'd start with 30 psi, on hard, dry, flat and smooth surface.

If the chalk wear is not even, test again with 2 psi increase or decrease, according to the first result.



Rim width affects chalk test result.
A rim which is wider than the tire specs, would allow the tire to cave in at what would have been the correct pressure.
So, for even tire wear and good road grip, the psi would be higher and the ride will be harder.
For a rim which is too narrow for the tire, it's the other way around.
Those who use wider or narrower rim width than the tire specs, and want optimal road grip and even wear, have to compromise -- higher pressure & harder ride, or lower pressure and somewhat mushier steering feel.