Sorry OP, but my guess is that your problem is not just going to go away as you wear in the tires...

We have the same setup and same problem. I started having PSM problems around moderage speed corners ever since putting on 997tt wheels. My 997tt rims came with front PS2's that were about 85% good at size 235/35/19 and I bought new Nitto Invos for the rear size 315/25/19. This setup definately has caused PSM problems around aggressive/moderate cornering.

Some people said that this might go away with wear on the new rears, but it really has not and the problem is still there after 3k miles. In fact, it happened today as well. Turning off PSM does not help. I have had my steering sensor reset by Porsche ($90) after the wheel install and it did nothing either. I also had the car aligned, nothing. I believe the true problem is the mismatched tires, more specifically, using the INCORRECT FRONT SIZE. The perfect setup for 997tt wheels on a 996tt is 315/25/19 in rear and 225/35/19 in the front (both are 25.2'' in height and thus have the same rotation), not 235/35/19 (which we both have!) which are really 25.5'' in height, so .3'' taller on the front. This rotational difference, coupled with the 996's viscious coupling is likely what sets off the PSM and causes our problems, although technically .3'' disparity is supposed to be ok. I am thinking in our case, it is not. The 997tt has an electromagnic system, and is much more tolerent of tire disparities than the 996 is. This is another reason why you cannot use stock 997tt wheel sizes for use on 997tt wheels installed on a 996. It will potentiall ruin your differential over time and will also likely cause the problems we are having.

My problem might have gotten a little better with wear, but I am not sure of this really. I did have PSM go off on a very moderate corner today. Yes, it is very unsettling as well and can scare the hell out of you if you are not prepared. It could perhaps even cause a crash if you are not paying attention with a firm grip on the wheel. Hopefully you figure something out, and PLEASE LET ME KNOW!!!, otherwise, I'm planning on replacing tires in the spring/summer. Notice that this PSM problem only happens at speeds above ~30mph or so (long round highway ramps being one example of a common occurance), below that speed I have no problem with PSM power sliding or whatever. My PS2's on the front are wearing fast too, so I may just try switching the front to Nitto Invo's at 225/35/19 if I can find them and see if that helps, otherwise maybe all four new tires since I'm not mismatching again, although thats pricy with these size tires since there is very limited selection for the rears. IMO, the Invo has held up great and grips well.

Here is my thread, read though it, there is info there: https://www.6speedonline.com/forums/...che-turbo.html .

Also, here's another relevant thread:

https://www.6speedonline.com/forums/...-behavior.html

Please keep me posted of anything you find out. Mostly I've learned to live with the PSM issue I think and avoid the aggressive cornering now that its winter with salt on the road, but I'll want to get this fixed for summer driving and also want to track my car this year.

 

Just to reiterate again in case someone misses it in my long above post, these are NOT the proper tire sizes for the 996tt with 997tt wheels. You need 315/25/19 and 225/35/19 for a perfect 25.2'' matching ride height and thus matching rotations.

What sucks is the rear tires have limited selection, and PS2's cost $550 each for the rears. I'm very happy with the Nitto Invos, and have heard good things about the Toyo TR1 as well that work for us. I wish Hankook would make thier V12 or whatever in our sizes!

 

MikeR--I read the posts --thanks for the links! I did not realize there was so many with similar issues. I have Nittos on the front now so they are the same manf. but they have 2k miles and the rears are new.

I had the same manf/sizes on before this latest switch on the rears with no PSM issue in 12k miles.

Nitto web spec sizes are as follows:

Inov 235/35/19 are 25.47" and 816 revs per mile
Invo 315/25/19 are 25.28" and 822 revs per mile
Not exact but within spec tolerance --less than .8% delta

Invo 225/35/19 are 26.2" and 798 revs per mile--almost 1"+

Invo 265/30/19 are 25.31" and 821 revs --are closest but 265 up front seem too wide and no side wall.

I am thinking that I the mold seal is still on the rears and I need to get some miles on them. But not 100% on any cause right now. The reason I am leaning on this as the root cause is because of my prior mileage with the same invo set and no issues.

What do you think?

 

Do keep in mind that the "30" is '30% of 265' so 35% of 235 is the same as 30 of 265 (more or less)

The point is you cannot look at the "% sidewall" and decide there is too much or too little absolute sidewall height.

 

you are correct-- I was thinking relative to the diameter is must be shorter, but in all likelihood it could be the same.

 

Sorry guys but everything I have read is very clear that for 19s 235/35 and 315/25 are the best combo to ensure minimum difference in rolling diameter. I had all sorts of similar weird issues with PSM when my earlier wrongly sized tires wore down past a certain point. To be fair though many have warned that different brands / models don't exactly measure up relative to their markings so perhaps for Nitto's that may be the case. I switched to the above sizes for Michelin PS2s and thankfully all my problems disappeared with no apparent long term damage... My experience for what it's worth...

 

After reading all the threads I have opted to go with the following tires sizes. It shows the least number of revs delta (4) resulting in a .0453% difference.

225/40/19
305/30/19

I didn't want to push the envelope on the width of the 315. These actually fill out the wheel well very nicely. I am also running 7mm spacers on the front and 14mm on the rear. Pics to follow tomorrow in the daylight.

I found this website very useful since you can input multiple tires sizes for comparison including OD, sidewall, revs per mile, tread width, everything. Hopefully this helps eliminate the issue with the PSM kicking in. I think the tire size discrepancy is the major player. I have had zero issues but few miles as well. I'll repost if my PSM kicks in.

http://www.1010tires.com/TireSizeCalculator.asp

 

See my response here: https://www.6speedonline.com/forums/...ml#post3099683

I think those tires you've chosed are too tall and will cause rubbing.