Maximum pressure available in garage is 34.8 psi. on race tyre
Pressing f12 only allows maximum pressure of 30.4 psi to be set.

If you run with any pressure greater than 30.4psi and try too add pressure via F12 'Pit Instructions' ,it always reduces your pressures and defaults to maximum 30.4psi

Not good during long race when you decide to increase those pressures a little and find you have lost 4 psi !!

After further testing in version Z,there seems to be more discrepancies in twelve of the cars ,and all tyre types.
Only seems to be on the rear.

FO8 - garage max 23.9 / F12 max 30.4

FOX - garage max 23.9 / F12 max 27.3

FBM - garage max 23.9 / F12 max 26.1

FZR - garage max 34.8 / F12 max 30.4

XFR - garage max 32.6 / F12 max 43.5

UFR - garage max 23.9 / F12 max 37.0

FZ5 - garage max 58.7 / F12 max 50.0

RAC - garage max 50.0 / F12 max 47.8

XRT - garage max 58.7 / F12 max 54.4

XRG - garage max 47.8 / F12 max 52.5

XFG - garage max 45.7 / F12 max 54.4

UF1 - garage max 39.1 / F12 max 43.5

(pressures in psi)

I found this bug while making a set for the GT Series , which forces use of R2 tyres.
Done a few laps in FZR, pressed F12 , tried to increase pressures from 32.5psi at pit stop, to find the pressure settings dropped to 30.4psi as soon as I pressed to increase pressure.

Are the rear pressure limits the same as the front pressure limits, perchance?

Yup , seem to be ,on the few I just checked