jrockwood

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

Fronts are less that 6 months old >2k miles

F: 235/3/19
R: 315/25/19

LVDell

What brand and model are the tires front and rear? Also I assume you meant 235/35/19 for F?

Bob Rouleau

Are the diameters of the tires very close to the diameter of the OEM tires? PSM gets upset if it sees different wheel speeds front to rear, often caused by a bigger difference in rolling diameter than the system is programmed for. You can use tire rack's specs to check. If the car is the one in your avatar, I suspect it was never designed for 315's in back.....

Best,

jrockwood

I did a ton of research here and elsewhere to determine proper size and manf. 235/35/19f and 315/25/19r nitto invo was my choice. They are within 1.5% delta front to rear size and +8 total rpm rolling delta.

I had the same sizes and same manf for 10k miles with no issues. The fronts have less than 2k mi on them.

I did remove the spacers in the rear prior to this round of swapping rears--could this have changed the camber/alignment thus spooking the PSM?

LVDell

Those sizes are just fine. The spacers should have zero impact on that.

Maybe it is the mold release agent on the tires that has no fully be released creating a slick tire condition triggering the PSM?

cannon1000

When exactly is it engaging? When you get on the throttle or just driving straight at highway speeds? If the first, I agree with LVDell...getting some minor slippage which will cause PSM to start taking over (feels weird when it does), if the latter, then you might need someone to look at it.

jrockwood

On throttle in tight high speed turns and on long high speed bends - like tight on-ramps. That was the first I felt it after the new tires... freaked me a bit --quick brake, shutter in the steering wheel and then grip.

Only time I have had the PSM engage prior to new rear tires was on WOT from a start. How long is a break in period for the new tires?

One thing I love about this car is it the most predicable and stable to drive of any car I have driven at high speed, yet now I am spooked guessing when the PSM is going to come on.

Is there are reset for the PSM to get new parameters? Do I need to pull the battery?

Thanks BTW for your help!

LVDell

The tire rack site recommends 500 miles (see below). With that said, I have heard a little as a couple hundred miles will do the trick.

Tires are comprised of many layers of rubber, steel and fabric. Due to these different components, your new tires require a break-in period to ensure that they deliver their normal ride quality and maximum performance. As tires are cured, a release lubricant is applied to prevent them from sticking in their mold. Some of the lubricant stays on the surface of your tires, reducing traction until it is worn away. Five hundred miles of easy acceleration, cornering and braking will allow the mold release lubricant to wear off, allowing the other tire components to begin working together.

cannon1000

Have you driven an Autocross yet? I did my first one a few months ago...first time I "REALLY" felt PSM engage...it was quite frightening at first...I had what seemed like ABS on the back left tire and power drop on others - at the same time! (I am used to my truck's DSC which will reduce power to a wheel to prevent spinning).

PSM can make your car do some funky things....but it works. I am sure it was keeping me from spinning on the AutoX course that day - which is fine by me.

I think you are just being too aggressive on your new rear tires - where most of the power is going ... so you have good grip on the front, but only like 35% (i don't remember exactly) of the power. I would get the tires heated up safely (long drive on an interstate is good where you can go faster legally) and get some wear on them as well - get them warm - pull into an empty parking lot and do a lot of S-turns to get some wear.

When I got new motorcycle tires I spent a whole day breaking them in...I was very cautious with them at first - get them heated up, find a nice empty parking deck and do ever smaller circles...first one way, then the other. When they were "scuffed" sufficiently - I quit worrying about them.

MK19

I've had the same experience with new rears using older front tires.......all stock sizes, stock wheels etc. I'm running Yoko Advan Sports. In my case it didn't really start until there were 4-5k miles on the new rears. I'll admit that the fronts probably have 25-30k miles on then and are at about 35% tread. In my case, it occurs under relitively light trurning, not under high loads.........but still un nerving as it seems the wrong brake is activating which upsets the car ........ie in a turn to the right where you might expect the rear to slip/swing out, the right front bake activates which torques the car even further into a clockwise spin. But its so momentary, and under light conditions, there's plenty of grip and no time to get into real trouble. Under these light loading conditions it might just be that the fronts are too cold to grip.

jrockwood

Great advise--after reviewing the scenarios and getting feedback, I think you are right. The weather is cold and been raining. The new tires are probably letting loose and PSM is doing what it is suppose to--nevertheless still a unnerving experience in a 65mph uphill twisty to get the shimmy and a brake pulse.

I will say that the ride is much better... quieter--the rears that I replaced were corded and flat across the mid line. Changed my oil and found the belts shredding on in the inside. Lots of road noise. I got 11k out of them. Should have replaced them 2k ago.