Max tire size on 9x18 rear wheel
 

Car: 2000 Boxster base
Wheel: 9x18 Turbo twist Porsche Factory Wheels
Rear suspension & camber: Car has stock suspension & camber alignment.

Currently I have 265/35/18 on the rear wheels.
Qn: what is the max tire size I can install in my 9x18 wheel without having to use any spaces, fender rolling, any rubbing and performance issues?.
Tire preference: Michelin Pilot Super Sport tires. Car will be used in both track and street.

Following are some options, let me know what you think:

Michelin Pilot Super Sport 275/35/18
Michelin Pilot Super Sport 285/35/18

Thank you.
Chamilka

You're already running the max recommended tire width for a 9" wheel.

Tyre Size for Rim Size/Width Calculator - What's the best tyre size for my rim?

Thank you, I didn't realize 265 is the max, I though I have heard people using 275 but may be that for 10 inch.
Thanks for you input and the link.

I'm not saying 275 won't fit. I would worry about the contact patch not being as good (since it will be putting a bow in the tire) as if you were running a 265 tire.

EDIT: I am curious as to your tread wear using 265's on a 9" rims.


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I've never had a problem w/ 275s on my 9" turbo twists.

Do you deflate the tire? How are you getting the tire to get full surface contact? A 275 tire is 10.83 inches wide.


Do you happen to have a close up picture of this combo?

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Here are a couple of shots of 275 on 9"
http://986forum.com/forums/uploads01...1427117209.jpg
http://986forum.com/forums/uploads01...1427117226.jpg
Just for kicks, here's 235 on the 7.5" wheel
http://986forum.com/forums/uploads01...1427117630.jpg

By this picture it looks like your under inflating the tire and still not getting full contact of the tire and it's showing the bow.

http://986forum.com/forums/uploads01...1427117226.jpg

I had 295s on my mercedes with 9 inch wheels. There is the recommended best size and then there's everything else

heck, many cobra guys ran a 315-35-17 on a 17x9 inch rim until the aftermarket companies made replicas to 17x10.5


Not saying you should put such a big tire back there but just because someone says its not ideal does not mean its not possible.

Not true. The Michelin 275/35 is suggested for a 9-11" rim.

It is too true. I said the recommended size, not what you can get fit on a rim.

Understand this, 9" rim, 275 tire is 10.83 inches wide. That's not a proper combination. Not even close. 265 is stretching the the recommended size for a 9" rim.

Please by all means ignore the tire/wheel site I posted.

This is the wheel I have decided to go with on my Boxster. Notice the rec tire size, from Tire Rack? 265 and that's on a 10" wheel. However I will be going with 275 tires on the rear.

http://i60.tinypic.com/ngovhw.jpg

I never said it was impossible. People do unrecommended things all the time, doesn't make it correct.

Not attacking just saying. And not correct does not mean it does not work. Just because a 265 will work ideally with a "XX" inch rim does not mean a 275 won't work better even though a 275 may work better with a larger rim. I love the big tire look, but in many cases it just does nothing but deter the performance.

Here is my old car with the big tire. Yes I know today most are into the other direction and like the stretched tire look but I'm old school.

http://mbworld.org/forums/attachment...29535rear1.jpg

I'm sticking within the recommend size for those wheels. 235 front, 275 rear. This combination gives a better front to rear tire speed rotation too.

http://i61.tinypic.com/xf42gj.jpghttp://i62.tinypic.com/2upzv3p.jpg

The are lots of things to look at when buying tires, way more then how wide a rear tire you can fit on a wheel.


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Yeah, I don't get the stretched tire deal either. Looks hideous to me.

On the rears I keep pressures at 34 psi. The car does have -3.2 degrees camber and it wears the inside edges. Since these tire are directional, about mid tire life I'll flip the tires on the rims and put them on the other side.

Loss of torque multiplication is the unavoidable downside of running taller than spec rear tires. This is very noticeable on 986's. That leaves a 285/30/18 as the only option along with 10" X 18" wheels. Now the car resists rotating into turns! :(

What's the recommended psi for those tires, 50?

I tell you what, the 275/295 combo on the benz sure was undrivable in the snow! Esp since they were summer tires they just floated on top of the snow... lol

And just to re-emphasize, when you have so much camber with a wide tire, and low sidewall, you will get a lot more tire wear than a narrower tire.

I'm not following you on this one.

Here is what my car originally came with.

http://i59.tinypic.com/sw4iev.jpg

This is what I'm moving to.

http://i58.tinypic.com/qrmbd5.jpg

Not only is the tire diameter smaller the front to rear tire rotation speed is much much better. The car should handle much better.


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Please please please send me photos of your car after you fit these on. I'm looking to buy the same.

Your car came with 265/35/...not 40 series

I also look at tire weight. I'd run 255/35/18 since it decreases overall dia, and weight and will provide me with enough lateral grip.
Tire choice within the mfg's range also determines how the tire performs because it affects the shape of the contact patch ie. how fast it breaks away in various directions. These ultra -low profile tires offer the sharpest response at the expense of a gentle breakaway and the widest 'approved' choice will provide the most lateral grip at the expense of a gentle breakaway to wheelspin and a locked tire.

Your right. I was going off this guys listing since my wheels got swiped before I purchased the car.

http://986forum.com/forums/boxster-parts-sale-wanted/54450-fs-porsche-boxster-18-carrera-light-ps2.html.

Always made me wonder why Porsche ran those size tires?

2003 Porsche Boxster Options & Packages Prices - Motor Trend Magazine

Anyways, with the 265/35 series the 275 is only 1.1% more in circumference size. Doubt one could tell the difference from seat of the pants and get the speedo closer to the actual speed of the car lol.

http://i61.tinypic.com/25ksyn9.jpg

1.1% the wrong way--decrease in overall gearing and increase in weight. 255 is win/win but no doubt 275 looks better. I ran 225 all the way around for 4 months and the only real difference was looks and the car was noticeably quicker. I think the 's' is overtired from the factory in order to keep people on the roads including the degree of stagger front to back. Sometimes less is more but no doubt bigger looks better.

Like I said 1.1% your not going to notice and since this is a daily driver it could offset the weight with lower RPM's and better gas mileage during my commute to work, which is 90% highway.

My car has 255's on the rear for the summer and there's just not enough grip for me. The rear end comes out too many times running my favorite twisties with those tires, which are Dunlop Direzza DZ101. I'm going with Michelin Pilot Super Sport tires and lighter OZ Alleggerita HLTwheels, think I'll be just fine with that combo.

If you didn't notice a difference in cornering capability with 225's, you're not driving hard enough to care. I could feel the difference in balance just going up 10 mm on the fronts. Wider tires will benefit cornering grip, with a minor detriment to acceleration.