A month ago I purchased a 2016 M Sport 340xi with staggered 19 inch M Sport wheels and can't wait to get up every morning to drive it. I live in Colorado and need to soon purchase some performance winter tires. Thinking of the Pirelli Winter Sottozero 3 in a 225 45 18 square setup. I contacted a local BMW dealer and was told that the suspension is tuned for the staggered setup and if I use a square setup it will cause handling issues (rear end will be loose). The BMW dealership recommended 225 45 18 front and 255 40 18 rear. From reading other forums many 340 owners have used a square setup for winter and nobody has mentioned a downside like poor handling. Please reply if you have used a square tire setup for winter and let me know what you think of the handling. I bought the car for the performance and don't want a significant compromise in winter. Will buy a staggered 18 winter setup if I have to.
https://www.bmwcca.org/forum/index.php?search/18609031/&q=square&o=date&c[user][0]=4814 (That should show search results of posts I've made mentioning the word "square") BMW's used to come with the same tire sizes on all four corners. Heaven forbid anyone actually know how to drive and manage a rear-wheel-drive car in today's world though. Ermagerd, sumbiddy might not actually experience or want perpetual hopeless understeer. It's a safety/liability thing from BMW's viewpoint - for liability's sake, the safest assumption is the skills and competency of all drivers are at best nominally above lobotomized zombies with zero learning ability or memory and micro-millisecond attention spans. If they under-width the front tires, then when insert-generic-no-skill-driver-here drives way too fast into a turn failing to brake adequately in advance (or just idiotically turns when going too fast), and their instinctive reaction to the front understeering towards the outside of the turn is oh-gee-whoopsie-going-too-fast-I'd-better-slow-down-so-now-I-better-brake, the throttle-lift and it's weight-transfer to the front axle with corresponding slight boost in front traction due to the now-slightly-larger-tire.contact-patch will have the car coming back to a pathway that keeps it on the road, without the butt-end of the car simultaneously saying buuuh-bye-I'm-a-goin-out-thataway. With a square setup, the front will have more traction, therefore less understeer, and an increased possibility of an oversteer skid in certain scenarios or conditions. If you have decent car control skills, common sense, a sense of self-preservation, and aren't inclined to drive like a total idiot, there may be a reasonable chance driving around on the same size tires at all four corners is something manageable instead of the potential-death liability freakout it may be from BMW's view. The advantage of narrow snow tires is changing the proportions of the shape of your contact patch - a narrower tire has less snow to push out of the way, for the same fore-aft contact-patch length you'd have with wider tires. 225's all around might be just perfect for what you need in Colorado winters, I don't know what you have to deal with - but, I suspect a 225 would be on the narrow size on the whole given the size & weight of the car. You'd have to be cautious all the time in winter driving about skidding due to the reduced lateral grip with the narrower size. Whether that's the appropriate tradeoff for your winter driving is your assessment. I'd say call the Tire Rack and talk to someone, they should have pretty good advice in that regard. Me personally, I like Michelin snows. For Colorado, Blizzaks might be the bomb, with their hydrophilic compound for about half the tread-depth - presumably the winter weather conditions there mightn't have you wearing out the best part of the winter tread compound prematurely. Here in SW Ohio, the very occasional ice-storm and highly-variable winters typically wouldn't justify using blizzaks - they'd just get worn out too fast on dry pavement running. Offhand, I'd guess maybe a compromise width perhaps might be something like a 235 or 245 all around. Personally I tend to like slightly larger dia. snows than stock for a slight boost in ground clearance (I'm rarely much concerned about speedometer variation), plus I'll go for the lightest, smallest dia. wheels to reduce unsprung weight and be able to run as much sidewall as reasonably possible. Yes, you get more sidewall rollover (which goes back to taking it easy on turns and not flying around like a crazed banshee), but it also softens the ride a bit - I couldn't say definitively, but I think a little additional give there has the potential to help grip in low-traction conditions, vs. potential having a wheel/tire combo bounce more. As for me, a square setup doesn't bother me - I don't want a staggered setup on any of my vehicles; you'll have to judge & decide. With your all-wheel drive system, it's important front & rear axles stay within a certain range of their rolling diameters lest too much of a difference freakout the traction control systems. No problems there with a square setup. If you have a limited-slip-differential, great. If not, not that big a deal with the all-wheel drive... but, I'd recommend leaving the traction-control systems enabled. The combo of awd, no LSD, & all traction-control off one time with an injudicious throttle punch caught me out and had me scrambling to (luckily) avoid power-skidding into a pole - so, I would heartily recommend not doing that! Note, running narrower widths than the stock rear 255's means exercising some judicious caution and restraint in winter driving when transiting all curves (large or small), turns, & corners. Throwing a 255 up front though might mean fitment issues, including wheels, and for winter driving, the higher width has the potential to make slogging through snowpack more of a problem, compared to something narrower. Not being able to run the same spec wheel all around also means not being able to swap tires front & rear to even-out wear.
Appreciate your prompt response and comments on BMW's engineered understeer. I have had the fortunate opportunity to do 10 BMW CAA high performance drive schools, including two days at Laguna Seca during the 2013 Oktoberfest. I have learned a lot from the incredible instructors and will continue to do so in the future. One day I will own a rear wheel drive BMW but it can't be my only vehicle based on where I drive in winter. I will contact TR and get a recommendation for a 18 inch square setup. Last question is on camber adjustment. Can I just bolt on the new 18 inch tire/wheel setup without camber adjustment? Don't want to assume the camber setting is the same for square vs staggered setup and potentially wear my new tires prematurely.
I've never heard anyone or place suggest swapping wheel/tire setups would necessitate adjusting or changing camber. Typically BMW camber settings are zero degrees front, with some neg. camber on the rear wheels (for stability & handling - helps to somewhat otherwise delay the onset of oversteer). That's why swapping tires front to rear & vice-versa at intervals evens out tire wear (and is a plus of a square setup). The fronts wear evenly across the tread-width, the rears wear the inside edges, and swapping them changes the wear areas. Around every 5k miles is probably pretty good, or, using snows - seasonally presumably would be ok too. Mark your snows with a grease pencil or something, or make notes of what's to go back on where for the next winter; easy to lose track!
