What kind of pressure are you using in the Run Flats? Is 40-42 too high.

 

The door sticker on my 2012 MCS calls for 33psi f/r.

I'd lowered to 30, to see how that would affect the RFT's somewhat-flinty ride (it helped), but a cool morning resulted in <27 in one tire that tripped the TPMS alert.

So back to 33.

It was delivered with 47psi all around. That was "flinty" riding indeed!

 

My 2009 R55 MCS (205/45-17 Dunlop run-flats) calls for 38F/38R cold... unless you are traveling over 100 mph. Then it's 41F/44R cold.

 

i ordered my countryman s all4 with the optional 225/45-18 tires

stock pressure is 32f/32r

the ride was brutal

the manual shows an optional pressure of 38/38 for "over 100 mph"

i tried that pressure and the change was dramtically better

so i borrowed a tire pyrometer, and i found the pressure of 42f/36r to be the correct pressures, giving uniform temperature across the tread

the ride improved dramatically as well as the handling

i was ready to ditch the runflats until i raised the pressure

i will keep them until they wear out

i suggest you beg/borrow/steal a tire pyrometer and set your pressures that way

scott

edit ... i should say that the 42f/36r pressures only apply to the oem 225/45-18 pirelli p7 rfs as fit on my cms all4, different cars and different tires may need different pressures, the pyrometer will lead you to the correct pressure for your car/tire combination

 

Same here (so much for dealer prep). Skipped at every bump.

 

My 2009 s convertible calls for 35...

 

It depends on the diameter of your rims. At 16" , it is lower at 32-34 psi and with 17" it is 36-38 psi. I like mine lower as the mini ride harsher due to its short wheelbase.

 

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Not meaning to hi jack the the thread, but is the tire pressure the same for run flats and non run flats?

 

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absolutely not!

i used a tire pyrometer, at the stock 32f/32r psi, the outer edges of the tire were hot and the centers were cool, about the same temp as the air, that means way underinflatedand also a brutal ride as the tire is riding on the sidewall

at 42f/36r, my tires are even temp all the way across, the tires are wearing evenly across the tread, the fronts and rears are wearing at the exact same rate, the ride is much better and so is the handling

scott

 

i will be able to tell you next spring when i replace my oem runflats with regular tires and set the pressure using the tire pyrometer

sometime in the next couple of weeks when i put my non-runflat winter tires on i will set the pressures with the pyrometer, but since i have no previous experience with winter tires, i do not know what to expect or if it would transfer to non-winter tires, but i will post the pressures i end up using

scott

 

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Ran 40# in 205/45-17's until I replaced them this summer!