Calculating Tire Stretch

[SourSamo]

Hey everyone,

I am working on trying to find the right sized tires for my new wheels, but really need some proper stretch to make them fit;

20x9 ET22 I think
20x10.5 ET25

This is M3 offsets on my E90 3 series.
Any help or guides on figuring out sizes? I have talked to a ton of local tire shops but they are no help.
Thanks.

[exexpat]

tyrestretch.com, rimtuck.com and willtheyfit.com are the tools you need. Since you have a 3-series, there are already thousands of them modified, so information is very plentiful.

[SourSamo]

Excellent thank you!
Looks like 225/35-20 for the fronts and 255/35-20 for the rears should tuck nicely