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Old 10-02-2012, 08:14 PM   #21
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Join Date: May 2007
Location: TX
Posts: 4,089
My Ride: 330i
Originally Posted by B_Cyrus View Post
I'm having a hard time believing this. 325i's come stock with like 195/50/16
Stock tire size for a 325 is 205/55/16, which results in an overall diameter of 24.87'', not too different than that of a 225/45/17, or 205/50/17, or 225/40/18, or 255/35/18 (all stock sizes).

The correct tire size combination for a staggered 18 inch set up is 225/40/18 fronts and 255/35/18 rears (for example, stock ZHP). The overall diameters are 25.08'', and 25.02'' inches respectively, the slight difference is negligible.

OP's problem is having incompatible tire sizes in the front and rear. He could have gone with 245/40/18's all around (even though not a stock size), or 225/40/18 all around (assuming wheel width allows). Putting one size in the front and the other in the rear is a NO GO.

Let me elaborate even further:

If you install 225/40/18 in the front and 245/40/18 in the rear, rear tires will be rotating 809 times per mile, while the fronts will be rotating 829.3 per mile, the difference is quite possibly large enough to be picked up by the DSC sensors. For the correct rear tire size, i.e. 255/35/18, revs per mile is 831.3, which is much closer to that of a 225/40/18 size tire, and the difference is within DSC's operating limits.

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