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Hey all, throwing this out there. M550s and M850s run a tire that is around 26.75" OEM diameter. The M5s and M8s run tires that are about 27.75" in diameter.
I've had the M550, two M5s and now have an M850. I feel the tires are just to small for this car - aside from being smaller by an inch in diameter, they also run 8" fronts and 9" rears - as opposed to the M5 & M8 at 9.5" fronts and 10.5" rears.
So, in the spring I am looking at new Vossen wheels and going to 9" fronts and 10.5" rears. I'd like to go up one profile, too, to gain that other inch in height (the wheel wells really need to be filled up a bit more - and it would ride a teensy bit better with more rubber in the side wall).
I took my M5 snow set down to the tire shop to have a look with them on the M850. They mostly fit, however the offsets are just a bit off, but the inch larger tire really looks good. They said a different wheel with the taller tire would be no problem.
I went to my BMW dealership and talked to the tire guy. He waffled about going up a tire size. He checked with the service techs. They said no, don't mess with the OEM diameter. I went to my performance shop guy where I am getting the new wheels. He said don't mess with the OEM diameter. With all the computers, AWD, DSC and what have you, the car could possibly not perform correctly.
If you keep the front and rear wheels within a 1% diameter tolerance between axels and go up a profile size, does the car really care if everything is rolling along, but at a 3% or so, different rate of speed on the axel rpm? I know people have gone wider all the time, but you never really hear about changing diameters that much. I know people do this, just don't know what the consequences are, if any, aside from a speedometer that will be slightly off. (I think it would bring the speedo speed closer to the true speed of the car, thus offsetting the 2-3 mph difference built into BMWs - if I remember which way the math works for this application. I could be wrong - maybe it's the other way around, but I don't feel like checking it now.)
Any thoughts appreciated.
Thx
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