Hello everyone, My wife needs new tires on her 2018 X3 M40i and I would like to get her Ultra High Performance All Season tires. I have been to Tire Rack where I usually do my comparisons but there are no options available in the current size on the vehicle, 245-40-R21 (Front) and 275-35-R21 (Rear). The top rating tire in this category on Tire Rack is the Continental Extreme Contact DWS 06 Plus (which I currently have on my E46 M3 and really like.) Those tires come a little bigger than what is currently on the M40i, so my question is does run or know if 265-40-R21 (Front) and 295-35-R21 (Rear) will fit? I have done the calculations and the front tires would be: .6" taller and .7" wider. The rear tires would be .5" taller and .8" wider. Please let me know your thoughts! Thanks, Mike
I use this to help estimate tire and wheel fitments, no experience with your car though. https://www.rimsntires.com/specspro.jsp Not that anyone wants the expense of extra wheels, but, personally, I prefer square setups for both the handling and ability to rotate tires. If I could determine if the rear size fit ok on the front, me, I'd downsize to 19" rims of the right width to run the same 275 width as the rear all around, which would soften the ride a bit and make for more comfortable daily driving while having more sidewall as protection against bent rims or blowouts from potholes, etc; also should make for less unsprung weight and allow the suspension to work better. Fwiw, the Conti DWS you mention is made in 275/45-19. In the long run, presumably, you recoup the extra wheel expense in getting longer usage out of the tires, with proper rotation. Typically, with staggered, the fronts would be fine for a long time but the rears are gone and you're stuck with the dilemma of replacing half-worn fronts also or if lucky having them last as long as the 2nd set of rears wearing out. However, not rotating as frequently, there is something to be said for the safety factor of being on fresh tires all around more frequently - better grip, rain (aquaplaning), etc. In that sense, one can justify not getting max wear out of tires since new tires, whatever they'll cost, is cheap compared to the consequences or potential consequences of an accident due to too-worn tires. If the car's a lease or won't be kept long term, the extra expense of wheels likely wouldn't be worth it. Also, one might prefer the aesthetics and looks of the lower-profile tires and larger wheels. With the AWD, the main thing probably is to keep the same ratio at least of the front and rear wheel/tire rolling diameters if you switch sizes. Otherwise, it's rubbing issues. You could look and measure wheel-well clearances to help guesstimate.
