# E36 M3 98 Tire upgrade to 18



## m3goalie (Sep 20, 2002)

Wanted to switch to some 18" rims. 
Probably some M parallel Wheels.

What would the suggested tire sizes Be ?

235/35/18 seems to make sense.
225/40/18 might also fit.

Does anyone know what would be correct or recommended.

Currently running Breyton Inspiration 17"x8.5 with 
225/45/17 and 245/40/17 Yoko AVS

Not sure what that new wheel sizes would do to the ASC it has.


Car is a 1998 M3 Coupe with ASC
Thanks


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## Dennis33 (Nov 4, 2003)

The best sizes would be:
- front - 18"x8" wheels with 225/40x18" tires
- rear - 18"x9" wheels with 245/35x18" tires 

The smartest size would be:
- front & rear - 18"x8" wheels with 225/40x18" tires
- you could rotate the wheels for even wear.


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## Bruce (Dec 24, 2001)

To keep the ABS and ASC happy you want the overall diameter to be +/-5% of the current setup. Check the internet for any number of calculators that can do this calculation for you. Also go to the Tire Rack's tech section and look at the plus concept stuff (+1 +2).


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## idratherbe007 (Dec 22, 2003)

Bruce, I found your +/-5% input quite helpful with regard to keeping everything (ACS/ABS/speedometer) happy. I did not find anything useful at Tire Rack's tech section on this topic. Do you have a specific link? I have not been able to get any help from the dealer (or BMW's web site) at all re up-sizing... Very frustrating!!! I have a couple of questions for you, regarding your +5% recommendation. My '99 M3 stock front is 225/45 and rear is 245/40. If I'm correct, the overall diameter is 25.1"/24.9" (front/rear). The question is, where to apply the 5%? Using the front tire as an example, 225+5%=235 (rounded down), 45+5%=50 (rounded up)... Resulting in a 235/50 which has a diameter of 26.6" and that is 6% over the stock 25.1" diameter. So... Would it be safer/better to apply the +5% to the overall diameter and look for a tire size that will put the diameter at 26.3" front and 26.1" for the rear (25.1+1.2=26.3 and 24.9+1.2=26.1)??? And, keeping with that 26.3/26.1, will I have any interference issues? 235/45, 245/45, 225/50 (front) are all under 26.3" and 255/40, 245/45, 255/45 (rear) are all at/under 26.1". Will any/all these sizes work ok? I'd sure hate to make the investment only to find it rubbing or interfering with something!!! Your expertise and words of wisdom will be much appreciated.


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## Bruce (Dec 24, 2001)

Not as good as I remember it but... http://www.tirerack.com/wheels/tech/plusone.htm

You want +/- 5% to be the overall DIAMETER, not tread width (the first number- i.e. 225), nor the circumfrence (although they are just different by pi)

Edit to add: http://www.miata.net/garage/tirecalc.html

If those 2 things don't help ask another question.

Really you probably can only fit 235s in front and 255s in back on a 99 M3.


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## idratherbe007 (Dec 22, 2003)

Bruce, Thanks for the prompt reply/post. The Miata tire size calculator is very handy and quite useful. My interest in this is visual esthetics (not performance edge). Personally, I don't care for the strait-up vertical sidewall look of the stock setup. I don't necessarily want to go wider but would like to achieve a more rounded look. Besides visual esthetics, this will also put a little more rubber beyond the edge of the rims. And what's so good about that? Well, in case I (or my wife) get too close to the curb, we'll be scrubbing the rubber instead scraping the rims. At any rate, the Miata calculator puts the diameter of the 235/50 (front) at 26.3 inches (5.2% over), BUT the Michelin Pilot Sport A/S data sheet says that the 235/50 is 26.6 inches (6.4% over). And, the Miata calculator puts the 255/45 (rear) at 26.0 inches (5.3% over) and the Michelin data sheet says that the 255/45 is 26.1 inches (5.7% over). Would 225/50 (3.6% over) and 245/45 (4.0% over) work better??? Is it your understanding that either the 235/50:255/45 or the 225/50:245/45 setup will work OK without any clearance issues??? This is going on the stock 7.5/8.5 rims. Assuming either setup will work without any clearance issues, which setup will give a more rounded look: The 235/50:255/45 or the 225/50:245/45??? Thanks again.


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## Bruce (Dec 24, 2001)

I think you options are more limited than you think. I don't recall anybody making a 225/50 or a 255/45. The normal sizes are 225/45 and 255/40 IIRC. You just need to go to tirerack.com and look at the available sizes. Most manufacturers offer the same numerical sizes (but that doesn't always translate into absolute widths- i.e. one manufacturers 225 is another 235 or 245- particularly true when talking about Hoosiers but we aren't talking track tires).


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## idratherbe007 (Dec 22, 2003)

Bruce, the Michelin Pilot Sport A/S:

http://michelinman.com/assets/pdfs/doc_pilotsportas.pdf

comes in all the sizes outlined in my last post (235/50:255/45 and 225/50:245/45). I know they are available at:

http://www.tiresavings.com/

Don't know if they are available at the Tire Rack. Apparently tirerack.com thinks that cookies are an essential element of ones ability to search for tire sizes.

I would still like to know which setup you think would work better, the 235/50:255/45 or the 225/50:245/45. And, is it your understanding that either the 235/50:255/45 or the 225/50:245/45 setup will work OK without any clearance issues??? This would go on the stock 7.5/8.5 rims. And, if both setups will work without any clearance issues, which setup will give a more rounded look: the 235/50:255/45 or the 225/50:245/45??? Thanks again.


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## Mantic6t9 (Jan 13, 2004)

What is the offset of the M Parallel? Is your car lowered? I'm running 18x8.5 Racing Dynamics with a 34 offset, tires are 225/40/18 Bridgestone SO-3s. My car is lowered on KW V2 coilovers so i have to run a 10mm spacer in the front to clear them. I think this is a great combo. If you have any further questions let me know.


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## idratherbe007 (Dec 22, 2003)

Mantic6t9 said:


> What is the offset of the M Parallel? Is your car lowered? I'm running 18x8.5 Racing Dynamics with a 34 offset, tires are 225/40/18 Bridgestone SO-3s. My car is lowered on KW V2 coilovers so i have to run a 10mm spacer in the front to clear them. I think this is a great combo. If you have any further questions let me know.


As far as I know, it's stock setup on original (standard) factory rims (7.5x17 front and 8.5x17 rear).


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