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      08-13-2013, 03:33 PM   #20
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Drives: M3
Join Date: Jun 2012
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Upon reading this thread we saw a few comments regarding tire sizes in regards to rubbing and would like to chime in with information regarding the F30 wheel and tire fitments.

The OEM F30 Sportline wheel is 18x8" ET34, and the EC-7's are 18x9.0" ET42. The EC-7's extends an additional 5mm on the fender side, while it takes up an additional 21mm of clearance on the strut side in comparison to the Sportline wheels. Also, since the EC-7's are an inch wider, this means that they are approximately 12.5mm wider per side of the wheel (half an inch wider per side of the wheel) than the OEM Sportline wheels. What this means is that using the same tire on the two different wheels will have different results, as the sidewall characteristics of the same tires will be different between the different width wheels. This may be the reason why some have not experienced rubbing issues with the 245/40/18 tire size.

Using the 245/40/18 tire on the 18x8" ET34 wheel is oversized, and due to the tires being ballooned with a narrower wheel, the tires effectively become ~240/40/18 since the tread is pulled in as the tire bead is pulled in. This happens when a tire is mounted on a wheel that is too narrow. Additionally, there would be less sidewall support from a wheel that is too narrow creating sloppier sidewalls, which in turn causes steering response to be less nimble and makes it more difficult to drive a tire at its limits. For street use this may not be an issue, but if one is looking for performance we do recommend the proper tire size and wheel width combination.