[rzm3]

So, I am considering track tires for my M3. A lot of people here mentioned the Cups, so I did a little research.

The Concept M3 came with 19" CSL + Cups:

Front: 235/35/19
Rear: 265/30/19

However, the OE 19s come with:

Front: 245/35/19
Rear: 265/35/19

So, using the tire diameter calculator, I computed the difference between OE and Cups:

Front: -4.891%
Rear: -4.13%

So, my question is: is such a big difference in diameter still going to be ok on the M3? Tire rack recommends deviating within 3% of the OE diameter.

Moreover, for 19" wheels, Cups only come in:

235/35/19
265/30/19
305/30/19
325/30/19

Thus, the 235 front and 265 rear seem to be the only possible choices for Cups to be used on the M3. There is a big difference in diameter on possible 18" wheels+tires also.

Advice? Comments?