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tyre size 996 turbo 19" wheels confused

turbolearner

Trainee
Joined
1 Aug 2013
Messages
72
Hi All,

need some new tyres.

currently have Kahn 19" RSC 2 Piece split rim alloy wheels. 8.5j front & 11j rear.

with 305 30 19 at the back and 245 35 19 at the front.

Been reading some posts about getting correct tyres sizes otherwise can blow the front diff
from what i have read the 997 19" tyre sizes are no good for the 996 turbo.
is anyone else running those size alloys, if so what tyre sizes are you using?

Thanks in advance


:?: :?:
 
The thing is everyone assumes on that thread that, for example, every 305/30/19 is the same rolling radius. They are not!

Tyre sizes vary from brand to brand. I recently saw the same spec N rated tyres on a Cayenne GTS: Yokohama and Pirelli. The Pirelli stood about 40mm higher.

I'm sorry I cant answer your question directly as I have no info to confimr otherwise.
 
Chris W said:
The thing is everyone assumes on that thread that, for example, every 305/30/19 is the same rolling radius. They are not!

Tyre sizes vary from brand to brand. I recently saw the same spec N rated tyres on a Cayenne GTS: Yokohama and Pirelli. The Pirelli stood about 40mm higher.

I'm sorry I cant answer your question directly as I have no info to confimr otherwise.

Surely by definition every tyre of that size should be the same rolling radius, they are the same measurements.
 
Hi,

seen that as well, where the quoted tyre size on the tyre is not the actual tyre size.

my current setup seems good, according to 6speed.

it says:

245/35-19 & 305/30-19. 783 & 769 rev/mile 1.7% diff.
Closer to stock and will likely be my next tire setup. These are also cheap and plentiful, guys have run them on lowered cars with no issues up front.

so i will stick with that.

Thanks alot, maybe someone should make a sticky with the tyre info.
 
So how many people have actually blown a diff? And was it due to incorrect tyres?
 
The front and rear rolling radius should match to better than 2% and with the rears being biased larger (if at all) - ie the 2% error is only POSITIVE.

Otherwise you'll get unwanted transmission windup in the AWD VC.

This results in an absolute new tyre rolling circumference being a maximum of circa 19 mm larger at the rear (the POSITIVE error allows for when the rear tyres are worn).
 
I'm pretty close then. 235/35/19 matches a standard 8.5J, and 295/30/19 on the rear is for a 11J, so the same tyre on an 11.5J will be about 25.5/25.7 rolling radius front to rear.[/list]
 
chriscoates81 said:
Chris W said:
The thing is everyone assumes on that thread that, for example, every 305/30/19 is the same rolling radius. They are not!

Tyre sizes vary from brand to brand. I recently saw the same spec N rated tyres on a Cayenne GTS: Yokohama and Pirelli. The Pirelli stood about 40mm higher.

I'm sorry I cant answer your question directly as I have no info to confimr otherwise.

Surely by definition every tyre of that size should be the same rolling radius, they are the same measurements.

Yes you would have thought so but see my below pics. Its a very common problem. We fitted a matching new set all round.

On 4x4's its one of the biggest issues.

I know of someone who saw a Cayenne at auction going cheap listed as 'gearbox issue'. Before the auction he checked the tyres and found they were mismatched. He won it, put new matching tyres on, gearbox whine disappeared and he sold for a £15k profit.

Cayenne 21":







Found on a 997 front 19":



Similar on this 20" off an Audi S5 - non Audi approved tyres are narrower.

 
e8_pack said:
Are they all mounted and inflated?

Excel have a good rep here so I'm inclined to accept Chris's advice on face value :D
 
Yes, its not a trick! :dont know:

I have one wheel wearing a 265/35/18 off a 996 and its width is about 30mm narrower, its quite astonishing what I see.
 
I wonder what tolerance these measurements are supposed to be done to?This is pretty shocking stuff, I wouldn't had believed it if I hadn't heard it from Chris.

MC
 
Wow! I am truly shocked.

How does say an n rated bridgestone compare to an n rated Michelin, are Porsche mire strict with their specs?
 

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