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Discussion Starter · #1 ·
Hi Guys,

Anyone tried these sizes on a 981?

1 guy says it won't work, due to 4,8% difference as where the maximum is 3%.
The other guy says he's running a setup as where the difference is 5,3% (265/35/18 F and 285/03/18 R).



So now I'm totally confused.


Br,

Tom.
 

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235/35 front should get you close. On most 981, except for GT4s, the front/rear rolling ratio should be about 1.02:1, where the fronts are smaller than the rears. The Porsche stability management system is calibrated to stock tire sizes and if you get more than 3 percent expected difference in rotation rates, the PSM will kick in and possibly brake the car unexpectedly or cut throttle or both.

Happened to me on drag strip with 235/40-19 and 265/40-19, stock sizes, and over pressured the front tires (to reduce rolling resistance) and under pressured the rear tires (for better traction at launch) and the throttle was cut at launch, creating an embarrassing situation where the car just sat for three seconds at the starting line with full throttle pressed. Setting the pressures even removed the issue.

In my current case with 245/35-19 and 295/30-19 tires, they have a 1:1 rolling ratio. I had the fronts shaved a bit to make them smaller and I run the fronts two psi lower than the rears. No problems yet.

With 235 fronts and 295 rears, this may exaggerate the tendency of the 981 to under steer at a track and will require a stiffer rear sway bar, a softer front sway bar, and possibly alignment and a new corner balance to put more weight on the front tires. This is why I had to go to an adjustable rear bar set at a stiffer than stock position and adjusted my front GT3 sway bars to the softest position and have a bit more weight on the front tires. The car is not quite neutral, but reasonably close.

V6
 

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I have a 2013 981 Boxster S and at HPDE use 255/35-18 and 295/30-18 without a problem in both Toyo R888 and Hoosier R7’s
 

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I used to run a 987 with the GT3 lower control arm mod at HPDEs. I'm looking to get back into track events with my 13 BS. Which wheels are you using with your setup?
 
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