Hi,I just bought a 997.2 carrera not long ago. I use 235/40/18 and 265/40/18 tire sizes.

When I drive on mountain roads, I don’t drive very aggressively, but psm will easily intervene in the brakes.

Where should I look for the problem? Four wheel alignment, tire size, or which side I didn’t expect.

It feels like the front and rear wheel speeds are different. The car thinks you are slipping, but it doesn’t.

You can’t enjoy the driving fun at all, and you are directly restricted by PSM.

 

Your rear is too large and the traction control detects your front wheels are running faster than the rears. You need 265-35-18 for the rear.

 

But the door frame sticker says 265/40/18

 

265/40-18 is the stock tire size for the C2 with the 18” Carrera IV wheels.

Turn it off then.

What tires are you running?

Having run 265/40-18 then switching to a 305/30-19, the grip is night and day. I was having PSM kick in all the time with the 265’s and the rear was more playful. With the 305’s it was night and day, no PSM flashes on the same road and same speed.

If you stay with your 10.5” Carrera IV wheels you can upgrade to a 285/35 or 295/35 rear summer tire and get more grip.

I am currently running a 235/40 and 285/35 Michelin Pilot Sport 4S. Might switch to the Conti Extreme Contacts 02 in 235/40 and 295/35 when the Michelins are done.

My car on 265’s:



My car on 285’s:

 

What does that mean? Is it ABS intervening when you are braking?

You are running stock tire sizes so tire sizing is not the problem.

 

I don't like that combo at all even if OEM sizing as yuyr rears are 3.6% different (larger) than your fronts. Go to a wider tire in the rear with an aspect ratio that better matches the front diameter.

 

As others have noted, that is the correct tire size from the factory for your 997.2 C2. Size isn’t the issue, but the tires themselves could be off…

What make/model of tire are you using?

Exact same model on both front & rear?

What’s the date code on the tires (to see if they’ve aged out)?

Please expand on the conditions where PSM has to intervene. For example…

Are you having directional instability under braking (i.e. PSM has to intervene to keep you pointed straight)?

And/or is the ABS intervening early?

In steady state cornering, does it intervene to address a front/rear balance problem (i.e. stop you spinning)?

Any unexpected understeer and/or oversteer behavior?

Any unexpected traction issue getting out of corners?

Thanks.

Karl.

 

After the chassis inspection, my left front shock absorber leaked oil... so it should be the main cause of the unstable driving

I'm going to swap out the shocks and get a feel for it