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      07-29-2015, 07:39 PM   #1
dvdtfiend
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okay I know it's still July....

...but I'm looking at winter tires since I'm about to buy OEM 18"s to serve as track/winter wheels.

Tire Rack recommends 235/40 square or 255/40 in the rear. Every one on this forum runs 40 series on 18s. Do 45s not fit? 225/45 + 245/45 are only 1% taller. They would be much better than the 40's for winter, especially since our cars have no RFT or spare and that can of fix-a-flat in the trunk does nothing for a blowout.

On the e46 m3, I had 17's with 45's, and they were good in the winter (still had a few pothole blow-outs though ), but no 17s with these big-ass rotors!

45's are still risky but 40's or 35's in the winter is just asking to freeze to death waiting for a tow truck on the Sunday night trip back from ski weekend , not to mention bent rims and control arms

Has anyone tired to fit a higher profile winter setup?
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      07-29-2015, 10:21 PM   #2
Amirsm3
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Quote:
Originally Posted by dvdtfiend View Post
...but I'm looking at winter tires since I'm about to buy OEM 18"s to serve as track/winter wheels.

Tire Rack recommends 235/40 square or 255/40 in the rear. Every one on this forum runs 40 series on 18s. Do 45s not fit? 225/45 + 245/45 are only 1% taller. They would be much better than the 40's for winter, especially since our cars have no RFT or spare and that can of fix-a-flat in the trunk does nothing for a blowout.

On the e46 m3, I had 17's with 45's, and they were good in the winter (still had a few pothole blow-outs though ), but no 17s with these big-ass rotors!

45's are still risky but 40's or 35's in the winter is just asking to freeze to death waiting for a tow truck on the Sunday night trip back from ski weekend , not to mention bent rims and control arms

Has anyone tired to fit a higher profile winter setup?
Your calculations are slightly off - but you're right, the variance isn't that big. Further down I'll speculate as to why the wider 255 was suggested. For reference, though...

245/45/18 overall height : ~26.68"
255/40/18 overall height : ~26.03"

That's roughly a 2.5% variance.

The OEM sized rear is 265/40/18, IIRC or: ~26.35"

Essentially, I think the real reason the 255 is suggested is because the 245/45 will stretch on the OEM 18" rear wheel (9.5" wide) - unless you're running a square set up of the front wheels (8.5" wide).
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      08-01-2015, 12:50 PM   #3
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I've ran square 245 40 winters before
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      08-04-2015, 10:34 AM   #4
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Don't be too hung up on the numeric aspect ratio. The actual physical dimensions are what matter.

225/45R18 has no more resistance to potholes than 245/40R18.

Taking the Blizzak WS80 for an example:

225/45R18XL - diameter 25.9", section width 8.8" load index 95
245/40R18XL - diameter 26", section width 10.2" load index 97

Height is the same, and the 245 actually holds more air because it is wider. The larger air chamber gives a bigger overall cushion to soak up bumps and impacts.

The wider tire will also protect the wheel better assuming you are running normal widths for the M3.

I've seen guys run the 225s and do fine, but if you're worried about impact the 245/40R18 is better.
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