I have the 18" wheels, 255 front 275 rear. Does anyone know factory recommended Snow tire size? Tire rack says I have to use the exact same size or traction control gets messed up. That just doesn't sound right to me. The dealer says They think I should 17" wheels but can't tell me the size until later in the year. Nothing in the owner's manual. Do not understand why it's such a mystery. Anyone know?
The dealer says whaaaat? If somebody at your dealership doesn't know how to find out exactly what fits on your car, then they ain't tryin' hard enough - that kind of info should be bread n' butter for dealer parts people.... There's this: http://www.realoem.com/bmw/enUS/showparts?id=8M93-USA-01-2017-F80N-BMW-M3&diagId=36_2462 It's a little confusing, the bottom one listing the 18" size, says for vehicles with carbon ceramic brakes but below that, a comment of not suitable for retrofit kit, carbon ceramic brakes. I don't know what that means, kinda sounds like if a car was retrofitted with carbon ceramics but didn't come with them, then that tire size wouldn't fit. Maybe 17's would fit, but if there's nothing on tirerack.com for 17" wheels for your car, then my guess would be the inner barrel of a 17" wheel wouldn't stand a prayer of clearing your front brakes. Checking TR for 2017 M3 sedan, it's only showing 19's, 20's, or 21's My guess would be what's important for the traction control system is the rolling diameter staying close to your stock wheel tire combo, which would also keep whatever difference in rolling diameter there is between the front and rear axle within a pretty close range. I don't know all the particulars, I think one part of the traction control working properly is it compares how the wheels are rolling against the other wheels, and there's normal operating parameters in the software & traction control computer programming, & having the wrong sizes can have the traction control thinking one wheel or both on an axle are slipping and then it's constantly trying to compensate, overworking the traction control system all the time even though there's actually nothing happening that requires the system.
Forgot to add, that was just checking TR for wheels - checking winter wheel/tire combos for an M3 w/ standard brakes, it shows 18's - 255/40-18 or 245/45-18; 19's: 255/35-19's all 4 corners, or alternately, that size front & 265/35 on the rears. If you're in an area where you expect to deal with a lot of snow, the 245/45-18's might be preferable - on snows, narrower means all the less snow the tires have to push out of the way, maximizing the contact patch grip longitudinally. Me, I'd go for either size of the 18's, since you get more tire sidewall height there vs. the 19's. If you're looking for runflats, looks like less options there - only 2 by Pirelli in the 19's, but in the 18's, there's also a rft Bridgestone, Conti, & Dunlop in addition to the 2 Pirelli's.
You will be fine to run the 18's on this car 17 will not clear the brakes, especially if you have carbon ceramic. As for traction control the size difference would have to be drastic or one tire different size than the others. Like garrison mentioned the 245/45/18 would probably be your best bet. As for your traction under power will change but with snow tires the traction under normal driving should remain the same.
Winter Tires: I purchased the following package (see attachment) in 2019 for 2018 M3. They are very good snow tires for winter driving. I used to live in MA, but now in VA. I do not encounter much snow in VA, but they are needed when the temperature drops blows 45F. The stopping distance in the car with winter tires is significantly reduced when weather drops below 45F. I estimate another 2 more years with the winter tires.
