Different Profile

[Colin_E]

I've finally stopped procrastinating & ditched the Bridgestone runflats for MPS4S all round. on my 2015 E89. Very happy with the way it has transformed the ride.
I went for same size (225/35 R19) at front but 255/35 R19 instead of 255/30 R19 at the rear. The fitters had inflated all 4 to 36psi which can't be right so I set about trying to establish what pressures to use.
Firstly let me say I don't want to resurrect the debate about pressures for runflats vs non-runflats - seems from a few searches that one has been done to death

However....

#1 Should the change of profile on the rears require more/ less or same pressure? Any online resource for this kind of info?

#2 Whilst trawling the web yesterday, I came across a suggestion that optimum tyre pressure can be found by inflating tyres when cold and driving for an hour & checking pressure again whilst still warm - if difference is more than 4psi , tyres are underinflated & if less than 3psi tyres are overinflated. Never heard of this before - any comments?

[Argyll Andy]

I ran my 35iS at 34F/36R on MPS4S’s took a bit of trial and error as they came out of the fitters way overinflated, 40 all round iirc.

Can’t help on the other bits but at the weekend on a forum run I never noticed any material difference between cold and warm pressures except for grip, and the tyres got very hot at some points

The G29 measures tyre pressure and temp and never flagged up an issue/variance throughout the whole weekend.

[dhobbs]

Sounds like a bit of trial and error is needed. Start with the standard psi then increase by 1 or 2 psi and see how it feels. If it squirms around a lot then under inflated. Ride gets too hard or jumps over bumps rather than holding the road, then over inflated.

I have seen the method you have mentioned but you have to do the same run each time you measure the pressures so can take a long time to do, so maybe better for track use than the road.

I've just gone up a profile size on my rear tyres 255/35/18 to 255/40/18 (e85 though) so a good thing for me to do as well.

[biZ4rreMids]

I went for same size (225/35 R19) at front but 255/35 R19 instead of 255/30 R19 at the rear. The fitters had inflated all 4 to 36psi which can't be right so I set about trying to establish what pressures to use.

I’m running the same tyre sizes as you on my E89 albeit Goodyears and pressures are 36R/34F and not experiencing any uneven tyre wear. When the tyres were fitted they were 40psi both ends and the ride was awful but after experimenting with different pressures found that 36R/34F offered the best comfort / performance.

[Colin_E]

I’m running the same tyre sizes as you on my E89 albeit Goodyears and pressures are 36R/34F and not experiencing any uneven tyre wear. When the tyres were fitted they were 40psi both ends and the ride was awful but after experimenting with different pressures found that 36R/34F offered the best comfort / performance.

That's useful to know
I've set it to 38R / 34F initially & I'll see how it goes.