Question about proper rolling diameter

[zeroboot]

For 22" wheels:

If I have 265/35 front and 315/30 rear, will that give me the correct ratio for proper rolling diameter front to back?

Thanks,
jb

[overheadvalve]

Front outside diameter with the 265/35 is 29.30 inches. Rear outside diameter with 315/30 is 29.44 inches so only a .14 difference. My OEM combination on my 335i has a .18 difference. I think you'll be fine.

[Draper]

It's unlikely, but you're best bet will be to check the specs for the actual tires you are looking at - 'revs per mile' in particular.

OEM revs per mile are matched exactly...any variation is done at your own peril.

[theaudir8fan]

Originally Posted by jzbm3

It's unlikely, but you're best bet will be to check the specs for the actual tires you are looking at - 'revs per mile' in particular.

OEM revs per mile are matched exactly...any variation is done at your own peril.

not completely true, OEM 20' bridgestones are matched exactly, OEM 21' dunlops and michellins all aren't the same. The way a tire sits on the rim, ie stretch and poke will also effect the rolling diameter

[Draper]

Originally Posted by theaudir8fan

not completely true, OEM 20' bridgestones are matched exactly, OEM 21' dunlops and michellins all aren't the same. The way a tire sits on the rim, ie stretch and poke will also effect the rolling diameter

Good call. So that would be your max variance, though personally I'd still prefer an exact match.

[eswimm]

3 revs per mile difference on those 22's. OEM 20's are less than .5 revs different. Still, only a ~0.5% difference and probably okay.

[theaudir8fan]

Originally Posted by jzbm3

Good call. So that would be your max variance, though personally I'd still prefer an exact match.

matching and as close as possible would defiantly be good, but i say up to 1% of variance should still be ok, truthfully no one will know until a problem occurs that can be attributed to it.

[Draper]

Originally Posted by eswimm

3 revs per mile difference on those 22's. OEM 20's are less than .5 revs different. Still, only a ~0.5% difference and probably okay.

This is based on nominal tire sizes, which can often times be misleading. You really need to look at the actual tire specs to get the rolling diameter and revs per mile. For example, the same spec Michelins will vary based on whether they have a star (BMW) or N1/N2 (Porsche) on the sidewall.

Originally Posted by theaudir8fan

matching and as close as possible would defiantly be good, but i say up to 1% of variance should still be ok, truthfully no one will know until a problem occurs that can be attributed to it.

I agree, no one really knows the threshold and probably no one ever will. There was one guy about a year ago who had a poorly matched set (I'm pretty sure it was over 1%) that did run into drivetrain issues shortly after installation.

IMHO, getting a properly sized set of wheels to go with a properly matched set of tires trumps any savings or 'look' you may get with a wheel brand that doesn't carry X5 specific widths.

[gan23]

If you look at the original tires
Dueler H/P Sport RFT
275/40R20
315/35R20

Both are 726 revs per mile according to the tirerack

The 21' kit I've installed is the same one as MY2015
Michelin
PILOT SUPER SPORT
285/35ZR21 721 revs per mile
325/30ZR21 725 revs per mile

I don't have any trouble at all and these are BMW approved tires.

[theaudir8fan]

the 21' dunlops are 723/728. By comparison, 22 pirelli 295/335 should have a much greater variance, pirelli doesn't list the rolling diameter for the front, but the rear is 722, the front is noticeably taller sitting on the ground, my guess would be the front is in the 715 range. Sometime there just isn't much choice as consumers

[PJB]

My 22in tyres are Pirelli Scorpions.

335/25/22. Bloody wide !