Bore Size and ET M3

[ajrettke]

I know the bore size is 64.1mm and bolt pattern is 5x114.3, ET +40mm. If I use hub-centric rings can I use any bore size larger than 64.1? And for the ET, I should subtract ~6mm per .5" increase in wheel width...i.e. stock is 8.5" and ET40, so 9" I should goto ET34mm is correct?

 

[emotiveeng]

Yes to hubcentric rings, assuming you do not have a Performance with the stepped hub lip.

Your math to match the OEM backspacing is correct, but there is room on the inside for a higher offset and room outside for a slightly lower offset. Depending on tire size, ride height, alignment, willingness to modify fenders etc. you can get away with +25 to +40, +30 to +35 being a fairly safe bet.