[Roman G]

EDIT: UPDATE----

Thought Id post some feedback for anyone undecided....

The car has been absolutely unstoppable in the snow, slush, rain. I take my car in the mountains all the time, all year long and in the winter (rock/ice climbing, fishing, camping, skiing and so forth)

Multiple times I've been in a blizzard this past winter and I have been blown away by the winter set up and not once have I been stuck or lost control (occasional small slide but nothing to even worth mentioning).

I went skiing in PA when a blizzard hit the area out of nowhere. The road takes you up a hill which is very steep for over half a mile going up. The snow rapidly accumulating. Steep enough that if you stop, you will not get going and simply slide back in the snow. I was behind a 4x4 truck with chains. I had multiple cars behind me. Cant stop and turn around because of oncoming traffic. The 4x4 with chains was sliding and fighting all over the place. He managed to stay on it. I was behind him, scared shitless thinking this is it, I'm f8cked, powering through with winters only with a small slide of about a foot to the side when I gave a bit more throttle. I managed through, happy, elated and blown away by the winter tires.

I think of my self as an excellent driver (don't we all) and I am a smart driver. If you want to drive with RWD and winter tires, you must be smart with the throttle, anticipate understeer, compensate and expect oversteer, and there is plenty of OVERSTEER fun in the RWD car with winter tires. You can have as much fun as you want with the car dancing on every turn or stay in control as much as you want. Be smart with the throttle, leave all nannies on (comfort mode is best for more gradual modular throttle in the snow).

I went with Michelin X-Ice Xi3s in 225/45/R17 and a set of 17s wheels in the same size from Tire Rack to clear the Msport brakes.

Having an 228 xdrive with all season tires prior to this car, I can attest that a RWD with winters is a far more capable weapon for fun and practicality and even safety than an xdrive with all seasons.


ORIGINAL POST------------
I'm settled on a Sport Line Track Pack 6mt which comes with a staggered setup:

225/40/R18 -front
245/35/R18 -rear

Will be running winter tires and the only winter tire available for the rear is the PIRELLI SOTTOZERO in the OEM size. I would like to run X-ICE xi3s or the WS80(leaning towards X-ICEs due to better dry pavement wear)

This will be my first time running a tire size other them OEM size and wondering if I can put a different size tire on a 8x18 rear than OEM size-245/35/R18. I've been playing around with the formulas and calculators and need better advice.

It seems that I can put 235/40/R18 on the rear and still be close to my diameter. The calculator says I can fit a 225/40(same as front) on an 8x18 size wheel. Is this correct? If so, I would just run 225/40 all around (7.5 front and 8inch rear), however I'm not too sure I can run a 225/40 on an 8inch wheel.

Please point me in the right direction as getting another set of winter wheels is not an option. I will only be buying tires.

Thank You,

Roman

[aerobod]

225/40-18 tyres can be used on 7.5" to 9" wide wheels, according to Michelin X-ice Xi3 specs. 225/45-18 tyres will also work on 7 to 8.5" wide wheels, I'm using that size of Sottozero 3 on 18x8 ET45 wheels all around without any rubbing, giving a bit more pothole protection and 12mm more ground clearance.

[Maynard]

I run a separate set of 17" winter wheels and tires. Easier in so many ways, vs. swapping seasonal rubber onto the same set of wheels (I also have that staggered summer setup, but narrow is better in winter). And IIRC it opens up the full range of brand options - I'm partial to Conti's myself but you can also go w/ Blizzaks, Michelins, or Hakki's.

[Roman G]

hmm the 225/45/18 is more attractive for more pothole protection (almost half inch of extra sidewall height) for the cheese grated NYC roads despite a floppier ride, but I can live with that to get thru the winters.

However, there is almost 3 inches difference of tire circumference and I've been lead to believe you don't want to have more than 1inch difference. Do you get any ABS lights or tractions lights?

Thank You

[cxp213]

The car doesn't know the difference between a tall tire and a short tire, or wide or narrow for that matter. All it sees is the rotation of the front wheels in relation to the rear. So if you change one end, you want to ideally change the other end just as much in the same direction (increase for increase, decrease for decrease) in terms of total percentage difference from their original size.

That said, cars generally allow up to around 3% difference from the opposite end to account for other similar sizes and tire wear. So, it's a total percentage, not an arbitrarily assigned number in inches (ex. 1" diff on a truck tire isn't the same as 1" diff on a Geo Metro).

Again, diameter change doesn't matter to the car as long as it's done evenly. What will matter is fitment of taller/shorter diameter tires since clearance can be an issue.

Another thing you want to keep in mind is that you don't necessarily want narrow tires as that reduces the protection it can offer to the wheel rim/lip/barrel due to the tire stretch, although I think there's plenty of sidewall in your example. Curbs (and other things) are harder to see in the snow, so I like similar width for my tires as my wheels, assuming it's not too wide.

[VMRWheels]

The 225/40/18 square setup would probably work best. The narrower tires tend to cut through snow better while a staggered tire setup may promote a bit of understeer. The 225/45/18 seems a little tall, but if others are running similar wheel specs with that size without any issues, it might be a consideration.

There are an abundance of quality winter/snow tires available in 225/40/18.

[aaaaah]

I endorse the 17" wheel and tyre setup as that will get you the extra sidewall you seek to absorb the potholes and also means you don't have to always pay for tyres to be switched.

[aerobod]

Originally Posted by Roman G

hmm the 225/45/18 is more attractive for more pothole protection (almost half inch of extra sidewall height) for the cheese grated NYC roads despite a floppier ride, but I can live with that to get thru the winters.

However, there is almost 3 inches difference of tire circumference and I've been lead to believe you don't want to have more than 1inch difference. Do you get any ABS lights or tractions lights?

Thank You

No ABS or traction control issues with the 225/45-18 tyres, the speedometer is now 100% accurate to the nearest GPS verified km/h. Tyres do vary a bit in size and cross-section profile for the same nominal size, but the 225/45-18 Sottozero 3s on 18x8 ET45 wheels all around I'm using have enough clearance from the wheel arch liners, struts and bodywork on full lock and suspension compression.

[GS235XI]

Anyone gone down to a 16" rim for winter.
My friend has a set of 205/55r16 that he will give me for cheap with the rims and like new snow tires but I don't know if they would fit the M235. Size chart shows they are practically the same overall height.

[aerobod]

No 16” wheels will clear the brakes on an M235i, some 17” wheels will, but not all.

[GS235XI]

Originally Posted by aerobod

No 16" wheels will clear the brakes on an M235i, some 17" wheels will, but not all.

Thanks