Max tire size on 9x18 rear wheel - 986 Forum - The Community for Porsche Boxster & Cayman Owners

chamilka · 03-22-2015, 08:26 AM

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

KRAM36 · 03-22-2015, 08:30 AM

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?

chamilka · 03-22-2015, 08:46 AM

Quote:

Originally Posted by KRAM36

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.

KRAM36 · 03-22-2015, 09:03 AM

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.

.

j.fro · 03-22-2015, 04:00 PM

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

KRAM36 · 03-22-2015, 06:03 PM

Quote:

Originally Posted by j.fro

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?

.

j.fro · 03-23-2015, 05:34 AM

Here are a couple of shots of 275 on 9"

Just for kicks, here's 235 on the 7.5" wheel

KRAM36 · 03-23-2015, 06:01 AM

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.

healthservices · 03-23-2015, 06:06 AM

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

healthservices · 03-23-2015, 06:20 AM

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.

stephen wilson · 03-23-2015, 06:31 AM

Quote:

Originally Posted by KRAM36

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?

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

KRAM36 · 03-23-2015, 06:45 AM

Quote:

Originally Posted by stephen wilson

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.

KRAM36 · 03-23-2015, 06:47 AM

Quote:

Originally Posted by healthservices

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.

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

healthservices · 03-23-2015, 07:14 AM

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.

KRAM36 · 03-23-2015, 07:21 AM

Quote:

Originally Posted by healthservices

Not attacking just saying. And not correct does not mean it does not work. Just because a 265 will work ideally with a 10 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.

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.

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.

.

KRAM36 · 03-23-2015, 07:37 AM

Quote:

Originally Posted by healthservices

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.

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

j.fro · 03-23-2015, 07:38 AM

Quote:

Originally Posted by KRAM36

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.

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.

BYprodriver · 03-23-2015, 07:39 AM

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!

KRAM36 · 03-23-2015, 07:46 AM

Quote:

Originally Posted by j.fro

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.

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

healthservices · 03-23-2015, 07:55 AM

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.