Originally Posted by gsrbri
Ben and guys:
Any thoughts/recommendations on inflation pressure for the winter tires? I went with the Tire Rack set-up with the 18" sport edition wheels with 235 and 255 Dunlop 3Ds.
I'm currently running the recommended inflation for the factory 18" wheels on the E90 M3, but this factory recommendation is for 10mm wider tires per corner (about 35 psi all around).
Any other ideas or calculations to be had?
The short answer: OE pressure should be fine.
Longer answer: Gross Axle weight ratings may vary slightly with vehicle options, but shouldn't be much over 2300 lbs F and 2650lbs R. At 35psi your 235 and 255 setup will carry (1312lbs x 2 tires) front and (1477 lbs x 2tires) rear. So you have plenty of capacity over and above the heaviest expected weight ratings for a fully loaded vehicle.
The front Dunlop is extra-load rated, and adding 3psi or so would bring it back to the load rating of the bigger tire, but as there is no corresponding benefit for the standard-load rear tire, and given that pressure recommendations are related to ride/handling characteristics and not just load, factory pressure seems to be the best way to go.
Information on load at specific pressures was obtained from appendix B here: