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      04-30-2013, 05:41 AM   #1
Messiah9000
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M-size tires on 3.0si coupe

Hello,

I am planning to buy new tires for my 3.0si coupe (Vredestein Ultrac Sessanta is on my shortlist). I our country there are lot of rough roads and potholes etc. So with my current factory spec RFT Bridgestones the ride is awful - tramlining, nervous, unstable, harsh, high noise etc. I want to go one hight level up, that means M-size tires. Stock 18 inch is front 225/40 and rear 255/35 and I want to go front 225/45 and rear 255/40. I have stock 18 inch wheels, 8 front and 8.5 rear. Has anyone tried M tire sizes with stock wheels? Comments I've read in different forums are not conclusive, some say rear will rub, some say it fits and drives fine.

Second question is that is there any tire manufacturers that make M-tire sizes without XL load marking? Sessanta is XL only. XL means higher load capacity and therefore stiffer sidewall. Stiffer sidewall means more tramlining and harsher ride. I've read a lot about tires the past few days and most folks say that Sessanta is the quietest and softest tire with XL marking. But does any manufacturer make this size without XL?

Thank you in advance!
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      04-30-2013, 06:07 AM   #2
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Buy hankook v12. Soft sidewall comfortable tire
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      04-30-2013, 08:14 AM   #3
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they should fit just fine, but acceleration and fuel economy will suffer.
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      04-30-2013, 08:17 AM   #4
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I did exactly what you are talking about when I had my 3.0si coupe. I was sick of the RFT's and wanted to change to regular tires. Bought M-sized tires which were slightly (very) taller. In fact, I bought the Hankook V12's. No issues at all with rubbing. Bonus was that the taller tires actually made the speedometer MORE accurate than before. BMW traditionally sets these to read a few mph's faster than you are really going. It was almost dead on after the tire change.
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      04-30-2013, 08:19 AM   #5
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it should fit....but your rough ride issue is more of a run flat problem than a small sidewall problem....like others said, fuel economy will change, and your speedometer will change
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      04-30-2013, 09:53 AM   #6
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I did not notice any increase or decrease in fuel economy. This is a VERY small change in the O.D. of the tire. If anything, I would have expected to see an increase in mileage since the O.D. is increasing.
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      04-30-2013, 06:33 PM   #7
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a change of over 4% in diameter is a large difference when comparing performance of tires in relation to engine and chassis dynamics.

as far as fuel economy is concerned, increased diameter will not only change the overall rear end gearing so that more fuel is required to get to X speed at Y time compared the smaller diameter, but it also increases rotational inertia which creates acceleration and deceleration issues. it's possible (though I believe highly unlikely) to over-lever the rear brakes on the non-///m due to the substantially smaller rotor size when paired with too tall of a tire.

if the car is being tracked, I personally would not consider this move. instead, consider a 235/40r18 front and 265/35r18 rear.
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      05-01-2013, 04:26 PM   #8
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Just ditch the RTFs. I did and all those issues you mentioned went away. Much, much better ride. Your rear could rub and you may need to do a fender roll to accommodate it.
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      05-02-2013, 08:50 AM   #9
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Thank you all for your help! I will stay with stock size and buy Michelin tires. I'm checking PS2, PS3 and PSS for prices and decide between those three. Which is the softest and quietest?
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      05-02-2013, 08:55 AM   #10
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they are all relatively equal on those terms...the pss are obviously the best performing, and maintain the comfort aspect as well
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      05-02-2013, 08:57 AM   #11
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^ +1
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      05-02-2013, 02:36 PM   #12
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One more for the PSS. Mine are great.
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      05-06-2013, 07:31 AM   #13
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In our country I cant get 255/35R18 rear supersports only ps3. Does anyone have experience running 265/35R18 tire on a stock 8.5 rim?
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      05-06-2013, 07:54 AM   #14
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Quote:
Originally Posted by Messiah9000 View Post
In our country I cant get 255/35R18 rear supersports only ps3. Does anyone have experience running 265/35R18 tire on a stock 8.5 rim?
here, post #62
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