Put new rear tires on 2 weeks ago and PSM engaging at frequent and unpredictable times. Can't drive aggressively---Spooky--any thoughts?

 

Front tires are worn out of spec compared to new rears. PSM can't compensate. I think you need new fronts as well bit I'm not a 996 guy so perhaps others may have a different diagnosis. Best,

 

I thought this might be an issue--but my fronts are barely worn with less that 2000 miles and had no issues before now. Now car feels unstable in tight corners when PSM engages.

F: 235/35/19
R: 315/25/19

 

Are they same brand FR/BK?

 

Yes nitto innvo

 

Alignment within spec?

 

I removed 1" spacers from rear when we put the new tires on... could that affect alignment or PSM? I had too much fender rub --cut my old tires

 

Aren't those the wrong sizes for a 996TT? Bit of a mis-match in tire diameters...maybe the newer batch of rears makes it worse? dunno

 

OP. do a search. There are a bunch of threads for compatible tire sizes with awd systems. I think the 996 is particularly sensitive with its viscous couplings. I don't know enough to have an opinion on what the removal of a spacer might do. I suppose it could change relative tire rotation in corners one side to the other and perhaps that has something to do with your issues. But that really is a WAG on my part.

 

Good advise-- The consensus at 6speed and at rennlist was this size combo for 19's. I had a new set of the same nitto's w/ these sizes for 10K+ miles with no PSM problems.

I did research on the tire size thoroughly before I purchased the first time around. Many nights reading long threads about front diff issues due to tire size mismatch. I love the search here.

The fronts were replaced about 6 months ago under warranty for a sidewall bulge. The rears I just replaced are same size as before.

I am going to check tire PSI --I imagine that with slightly worn fronts and excessive PSI on the rear they could be out as much as .5". Could this psych the PSM?

 

It would be easy enough to reinstall the spacers and rule that out as the source of the problem if that's all that changed in the replacement process.

 

And if that doesn't work, then I think you need new fronts regardless of mileage.

And if that doesn't work, then you should pay someone who really isn't making this up as he goes along. Good luck and best regards,

 

Ususally tire shops put a good 45-50psi to make them "set". If you don't deflate to something more normal sub 40 they can become pretty slippery, especially before they have been scrubbed in.

 

Now that I have had a chance to review what is going on and get feedback, I think that the rear tires are just not "scrubbed".

They must be letting loose because they are too new thus triggering the PSM. I have mostly been out in the cold and rain since the new tires. They probably just need some wear.

I will check back if they problem continues--thanks for your help everyone.

 

As Mr White suggests, check the tire pressure. Also, the Nitto Invo is a directional tire. Make sure that the shop didn't accidentally swap the left and right. There should be a "Rotation" arrow on the sidewall of the tire.