[Bimmer_Boy_22]

Originally Posted by CPT Smuggs

In case anyone else can benefit from my research which pertains to a F30 M-Sport xDrive:

To calculate tire height: ie 245/40R19

Take the width of the tire (ie 245mm)
then convert to inches (divide by 25.4)
then multiply by the ratio (.40)
then multiply by 2 (tire on both sides of the wheel)
then add the wheel diameter (19").

eg: (((245mm / 25.4) * .40) * 2) + 19" = 26.72" tall

*Don't exceed +- 0.5" the stock tire height to maintain your suspension, speedometer, comfort, etc.
*Try to stay as close as possible to stock tire heights.
*The speedometer comes ~1% fast, meaning a 1% increase in tire height will give you a true speed.

18" 400M (18x8 ET34 225/45R18 / 18x8.5 ET47 255/40R18) = 25.97" / 26.03" (stock)
19" 437M (19x8.5 ET35 225/40R19 / 19x9.5 ET40 255/35R19) = 26.08" / 26.02" REP (same as stock)
19" 437M (19x8.5 ET35 235/40R19 / 19x9.5 ET40 265/35R19) = 26.40" / 26.30" REP (+1.6% / +1%)
19" 437M (19x9.0 ET29 235/35R19 / 19x10 ET40 265/30R19) = 25.47" / 25.25" OEM (-2% / -3%) - Very popular with ACS / HRSport kits
19" 437M (19x9.0 ET29 235/40R19 / 19x10 ET40 265/35R19) = 26.40" / 26.30" OEM (+1.6% / +1%)
19" 437M (19x9.0 ET29 245/35R19 / 19x10 ET40 265/35R19) = 25.75" / 26.30" OEM (<-1% / +1%)
19" 437M (19x9.0 ET29 255/35R19 / 19x10 ET40 265/35R19) = 26.02" / 26.30" OEM (0% / +1%)
19" 437M (19x9.0 ET29 255/35R19 / 19x10 ET40 275/35R19) = 26.02" / 26.57" OEM M3 *Rubs!*

A 35 ratio tire is generally around 3.5" thick sidewall.
A 40 ratio tire is generally around 3.7" thick sidewall.

I personally like the thicker sidewall for comfort (at the cost of some handling) and to minimize wheel gap (I don't plan on dropping my car more than 0.75")

Thank you