Tire size

GregW / Oregon · 09-05-2007, 11:06 PM

Sorry if this is old news, but I just looked closely at the E92 M3 specs in the German press release, and discovered the rear tires are larger in diameter than the fronts.

Tyres, front/rear 245/40 ZR18 / 265/40 ZR18
Rims, front/rear 8.5J x 18 EH2+ IS 29 aluminium, forged/9.5J x 18 EH2+ IS 23 aluminium, forged

According to my calculations, since the aspect ratio is same front and rear, the rears are .40 x 20 mm x 2 = 16 mm ( 5/8") larger in diameter. This is confirmed by Michelin specs which show .60" difference (809 vs. 790 rpm) Anyone else notice this?

ChitownM3 · 09-06-2007, 12:07 AM

What?

GregW / Oregon · 09-06-2007, 12:15 AM

Quote:

Originally Posted by ChitownM3

What?

What, what? The E46 M3 used 225/40/18 fronts and 255/35 rears (subtract .05 aspect ratio for 19s). That results in front and rear tires of about the same diameter. If the specs are true for the E92 version, the rears are larger in diameter. This does not mean anything in particular, it's just a departure that I don't know has been previously recognized. If the diff ratio is lower (which it is at 3.846), the larger tires are offset to some degree in overall drive ratio.

aerisolphaln · 09-06-2007, 01:00 AM

Quote:

Originally Posted by GregW / Oregon

What, what? The E46 M3 used 225/40/18 fronts and 255/35 rears (subtract .05 aspect ratio for 19s). That results in front and rear tires of about the same diameter. If the specs are true for the E92 version, the rears are larger in diameter. This does not mean anything in particular, it's just a departure that I don't know has been previously recognized. If the diff ratio is lower (which it is at 3.846), the larger tires are offset to some degree in overall drive ratio.

Hmm, and what does all of this mean?

I think that's what his "what??" was all about...because it's my "what??" too.

ChitownM3 · 09-06-2007, 01:53 AM

Quote:

Originally Posted by aerisolphaln

Hmm, and what does all of this mean?

I think that's what his "what??" was all about...because it's my "what??" too.

Haha, right!

thekewl1 · 01-23-2008, 01:53 AM

Quote:

Originally Posted by GregW / Oregon

What, what? The E46 M3 used 225/40/18 fronts and 255/35 rears (subtract .05 aspect ratio for 19s). That results in front and rear tires of about the same diameter. If the specs are true for the E92 version, the rears are larger in diameter. This does not mean anything in particular, it's just a departure that I don't know has been previously recognized. If the diff ratio is lower (which it is at 3.846), the larger tires are offset to some degree in overall drive ratio.

i was noticing the same thing. why are the rear wheel rolling diameters larger than the front wheels? Will that have any negative effects?

09-05-2007, 11:06 PM	#1
GregW / Oregon Commander-In-Chief Drives: 2008 M3 Coupe, 2006 ML350 Join Date: Nov 2005 Location: Lake Oswego, OR Posts: 6,051 iTrader: (1) Garage List 2006 M-B ML350 [0.00] 2008 E92 M3 Coupe [4.75]	Tire size Sorry if this is old news, but I just looked closely at the E92 M3 specs in the German press release, and discovered the rear tires are larger in diameter than the fronts. Tyres, front/rear 245/40 ZR18 / 265/40 ZR18 Rims, front/rear 8.5J x 18 EH2+ IS 29 aluminium, forged/9.5J x 18 EH2+ IS 23 aluminium, forged According to my calculations, since the aspect ratio is same front and rear, the rears are .40 x 20 mm x 2 = 16 mm ( 5/8") larger in diameter. This is confirmed by Michelin specs which show .60" difference (809 vs. 790 rpm) Anyone else notice this? __________________ Greg Lake Oswego, Oregon, USA 2008 M3 Coupe - Alpine/Fox Red/Carbon 2001 M3 Coupe - SOLD 3/08 2006 Mercedes-Benz ML350 (2012 ML350 BlueTEC on order) Last edited by GregW / Oregon; 09-06-2007 at 12:49 PM.
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09-06-2007, 12:07 AM	#2
ChitownM3 Lieutenant Drives: 2001 SS Camaro Join Date: Jun 2007 Location: Burbs of Chicago Posts: 476 iTrader: (0)	What?