[luke1990]

Hi guys,

Peculiar - and maybe very simple question . I'm going from 245/40 275/35 R19 at recommended 2.2/2.6 bar to 255/40 and 295/35 R19. Since the tire size changes, I assume I need to adjust the pressure accordingly. Could you please check my understanding - if its correct?

The way I see it its about the sidewall. We know how BMW scales it:

245/40 + 275/35 R19 has 2.2/2.6 bar recommended
245/35 + 275/30 R20 has 2.5/3.0 bar recommended

245s going from R19 to R20: -12.8% sidewall and +13.6% pressure (2.5 vs 2.2)
275s going from R19 to R20: -15.8% sidewall and +15.4% pressure (3.0 vs 2.6)

This means that the pressure adjustment is very proportional to the sidewall change. I would think the difference comes from the fact that you round the pressure.

Hence with my setup:
255 vs 245s: +2.6% sidewall so run 2.1 instead of 2.2 for -4.5% pressure or 2.15 for -2.3% presure
295 vs 275s: +7.9% sidewall so run 2.4 instead of 2.6 for -7.7% pressure

Resulting setup on 255/40 + 295/35 R19: 2.15/2.4 bar. Am I right? Thanks! I think my calc makes sense but would like a confirmation