I have an '04 X50 with 19" HRE's on it with Hankook Ventus V12 tires. The car is stock other than a GT2 front bumper and the wheels. I've been driving 996 models for years and many miles now and I've never run into this problem.

I recently replaced the rear tires with some new ones. The fronts are 235/35-19 and the rears are 305/30-19. The fronts are 1/2 worn and I was replacing the rears after about 8k miles and left the fronts per the normal change the rears twice as often as the fronts schedule. After the change, the PSM started engaging when I go around turns, especially left turns. This is when I'm on the highway or even on local roads and I take a really sharp mountain turn at 30 mph. It also engaged when I was going straight yesterday and was running it up to about 120 mph while getting onto a highway. It was a little frightening to suddenly have the PSM kick in out of nowhere at that speed and it started to make the car go side to side at triple digits.

If I turn the PSM off, it seems to go away, but then I have another weird behavior. The ABS kicks in really easily, especially if I brake while turning. It seems to just be the front right wheel that's doing it, whether it's the PSM kicking in, or the ABS when the PSM is off.

I've had another weird problem that doesn't make sense. Twice I've triggered a flashing CEL when the front right wheel has hopped at 120ish mph and lost traction. A flashing CEL is supposed to be due to a misfire, but that's not the problem.

I wonder if I have a bad ABS sensor, or if it's the rotational difference of the tires that's doing it. Anybody else ever run into this problem?

 

The car was set up for 18" wheels and specific tire sizes. My car came with aftermarket wider 19" wheels and plus 1 tires that tend to cause the PSM and ABS to get a bit instrusive. For fun I put a stock set of 18" wheels and tires on and the problems when away. PS I'm running 315/25/19 on the rear.

 

The problem is the fact that you put on the wrong size rear tire which is too tall vs the front. The fact that the front is worn and rear is new makes the discrepancy even greater. You need a 315/25/19 on the rear to go with your 235/35/19 front. Your fronts, since they are smaller, are rotating faster than the rears and the PSM is interpreting that as a loss of traction on the front and thus intervenes. And you are trashing your viscous coupler with your set up......

 

I had similar problem when I swapped out my rears only.

I had to drive with pasm off because it would randomly go off when going around a turn.

It went away after about 1kmi. I guess that's when the rear tires got more settled in and firmed up. It was much less of a problem when I did both fronts and rears because they were both soft.

I would stay below 100mph until your rear tires get broken in.

Hope this helps.

 

You need 315/25/19 on the rear.

 

wrong size. should be 225/35/19 & 315/25/19. You can also use 235 in the front

 

Unfortunately, they don't make a 315 width in the Ventus. I looked for one before I bought the 305 again.

A 225 seems awfully narrow up front with the 315 in the back...

 

225/315 combo is 0% Rolling Diffrence front vs back...