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YOUR RESEARCHtires sizes for 18" NB
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Install ve wheels, 18 x 11" in in the rear
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My car ('02 C2, no pasm) is lowered and I just installed VE wheels, 18 X 11" in in the rear.
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A good reference that I use for tire sizes is Tire Rack.
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Suggestion · Original poster
If I were to run 235/40-18 and 285-35-18 it would come out to 645.20mm and 656.70mm.
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Suggestion · Original poster
I've searched the forum and it seems like some folks are running 235/40-18 and 285/35-18.
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I'm looking to get some new tires for my NB 996. I have OEM 18" on my car so the sizes are 225/40-18 and 285/30-18.
In the OEM size, I can get some Bridgestone SO4s. However everyone raves about the MPSS. Unfortunately the MPSS don't come in the proper OEM size. I've searched the forum and it seems like some folks are running 235/40-18 and 285/35-18.
Does anyone running those sizes have any comments about them? Does it have any effect on the traction control or ABS? (I have an LSD as well if it makes a difference)
The difference between the tires seem somewhat significant.
224/40 vs 235/40 has a diameter variance of 1.26%
285/30 vs 285/35 has a diameter variance of 4.54% (this is over 1" diff in height)
Based on my reading/research, it's recommended to stay within 3% or less variance.
So what say everyone? Has anyone run the 235/40 (not worried about this since the variance is so small) and the 285/35 (worried about this) long term with no ill effects? What about on the track?
Would a 275/35 makes sense or is giving up 10mm on the width not a good trade off? Are there any other tire sizes to consider?
EDIT: Forgot to mention I'll be putting my x74 suspension on as well so the car will be lower than stock. I also have the standard 7/15mm spacers which may or may not be installed at the same time. So hopefully these won't cause rubbing issues.
On the 2wd car, there are no side effects of having 285/35/18 tires. I had them for a year now. Car sits taller off the ground, great for my uses. No warning lights. I can climb more curbs, jump speed bumps, and drive the car off-road a little easier.
C4 is AWD. F-R tire size variance generally has to stay within 3% on the AWD cars to prevent any damage to the AWD system. Although some people claim that 996 system with viscous coupling is forgiving enough and can tolerate the higher size difference. I have not tested this theory, but someone with C4 can chime on this.
On 2WD cars main concern about tire size is ABS/TCS/Stability idiot lights going off due to the speed variance being outside the system tolerance level. I have not had any issues with idiot lights since I bought the car last year.
So OEM sizes are 225/40-18 and 285/30-18 respectively. This comes out to 637.20mm and 628.20mm overall diameter for each tire. So the fronts are taller than the rears, but only by 9mm.
If I were to run 235/40-18 and 285-35-18 it would come out to 645.20mm and 656.70mm. The delta here would be 11.5mm taller in the rear.
Just for reference, here are some other sizes I calculated:
275/35-18 649.70mm
265/35-18 642.70mm
In theory, either of the 275 or 265 would be closer to the overall diameter of the front, but the tradeoff would be a tire that isn't as wide.
But based on others, it looks like 285/35-18 will work. Just wanted to make sure it doesn't mess with the LSD and traction control. (Plus if/when I put the x74 in, the taller tires will actually raise the car back up a little bit -- haha)
I will speculate that you have a '99 based on the LSD and traction control. According to the manual for my '99 the rear size is 265-35-18. I think MPSS's are available in that size.
Tires are never the exact size of the marking on the sidewall. I think Michelins trend towards the larger size and I've heard that some cheaper tires are smallish, but that is all hearsay.
A good reference that I use for tire sizes is Tire Rack. Look under the specifications section of the tire you are interested in. It will tell you all you want to know and allow you to compare sizes.
I run MPSS in the sizes that you are questioning. My car ('02 C2, no pasm) is lowered and I just installed VE wheels, 18 X 11" in in the rear. No ABS issues, no rubbing and my fenders are rolled, too. She is set up with a bias towards track but not maxed out on camber etc., since I still driver her, quite frequently, on the street. The thoroughbreds get exercised at the track, plenty, and no worries. GL
I have 285x35x18 and 245x40x18 MPSS 0.533% difference in rolling diameter and fills the guards nicely. Speedometer is nearly spot on now and way more comfortable than the 265x30x18 and 235x40x18 bridgestones that were on it previously.
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