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Installed two new Michellin primacy mxm4 GREEN on the back - now car unstable

Aug 14, 2012
161
10
I just installed two new mxm4 on the rear. First ride after picking up the car it felt unstable and a bit scary above 75mph. Even when going straight. Changing lanes or taking curves at high speed requires two hands on the wheel. It has been two days now and i still think car is unstable.

The front is also mxm4s with 5/32 depth of tread left. I changed the rear because of bulge in the one of the tire walls.

Any ideas.

Car has 56k, 2012-S85 air suspension. This is the second set of mxm4s. the first set was great.



Thanks.
 

mspohr

Well-Known Member
Jul 27, 2014
9,624
11,417
California
I just installed two new mxm4 on the rear. First ride after picking up the car it felt unstable and a bit scary above 75mph. Even when going straight. Changing lanes or taking curves at high speed requires two hands on the wheel. It has been two days now and i still think car is unstable.

The front is also mxm4s with 5/32 depth of tread left. I changed the rear because of bulge in the one of the tire walls.

Any ideas.

Car has 56k, 2012-S85 air suspension. This is the second set of mxm4s. the first set was great.



Thanks.

Change all four. Cars don't do well with mixed tires.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Mar 8, 2012
19,802
23,163
Texas
Msphor is right. Change all four. Also check the tire pressures to insure they are at least at the vehicle placard pressure and equal front to rear.

Tires are a lot like wallpaper. It's best if you get all four from the same batch.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,024
1,014
My experience is that the Michelin Primacy tires are a much harder compound than the other tires I've had on my car. It's much easier to get the car to spin them or slide on them compared to the various other tires I've had.
 

tstafford

Active Member
Jul 4, 2015
1,039
245
Nashville, TN
I'd take it back to where you had the work done and talk to them. Sounds very odd to me. And I don't buy the arguments that you need to replace four at the same time.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Mar 8, 2012
19,802
23,163
Texas
also check they are XL rated, the MS is a heavy car
If not the sidewalls may not be specced fully up to the job

The difference in the carcass between SL and XL tires are minimal. The individual cords of the carcass have a few more threads, but that's all. "Heavy" doesn't matter unless you also consider tire size. (An XL tire is sometimes used with a smaller than normal tire size for a particular vehicle). There is no way that XL vs. SL would affect handling in a given model tire. Unless two tires are SL and the other two are XL.

- - - Updated - - -

I'd take it back to where you had the work done and talk to them. Sounds very odd to me. And I don't buy the arguments that you need to replace four at the same time.

I've seen way too many instances when replacing two tires causes the vehicle to go squirrley. Tire manufacturers make changes all the time and more often then not don't publicize it, which is why it's best to replace all four tires. However, with any new tire, a period of moderate driving is required to remove the mold release. If there is still a problem, swapping the tires from front to back will sometimes solve the issue. If that fails, an alignment should be done.
 

AmpedRealtor

Well-Known Member
Jun 30, 2013
6,397
3,367
Phoenix, AZ
The two new tires on the rear may have also changed some of your alignment numbers. Per my service advisor, a previous alignment with older tires will no longer be valid with new tires. Definitely have your car re-aligned. What you are experiencing sounds like out-of-spec toe.
 

tezco

Sig P85
Nov 9, 2012
819
4
Colorado
I'm with Jerry on this one. A friend borrowed my truck once and blew a tire. His tire shop put two new bias ply's on the rear. Unfortunately, the fronts were radials. Talk about degraded handling....
 

pdx4s

Member
Jul 16, 2013
23
1
Portland, OR
similar experience, installed 4 brand new MXM4 same exact model as the original ones, scary unstable in the first 100mils, some what better after that, now have 550mils on them but... significantly higher energy usage (av. 340whr vs 290 with the old tires) with big at lower speed, pressure is 45.5psi on all 4, if not improving will be going back to Discount Tire to check what's wrong with them, not sure they are qualified to perform alignment.
 

vgrinshpun

Supporting Member
Apr 5, 2013
5,886
22,790
PA
If the new tires were installed by an independent shop, I would make sure that lugs were properly torqued to 129lb-ft, per the Manual. This is unusually high torque specification, and not many tire shops are aware of this. If the proper torque spec is not mentioned by the owner, majority of technicians will NOT torque properly.
 
Last edited:

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Mar 8, 2012
19,802
23,163
Texas
similar experience, installed 4 brand new MXM4 same exact model as the original ones, scary unstable in the first 100mils, some what better after that, now have 550mils on them but... significantly higher energy usage (av. 340whr vs 290 with the old tires) with big at lower speed, pressure is 45.5psi on all 4, if not improving will be going back to Discount Tire to check what's wrong with them, not sure they are qualified to perform alignment.

Discount Tire doesn't do alignments (at least none that I've been to do).

New tires have mold release on them, so you should drive conservatively for the first couple of hundred miles. Besides the mold release, the mounting lubricant may not be dry. In addition, the deeper tread depth of the new tires allow for more flexing of the tread compound. If you're coming from tires that are ready for replacement it can change the handling that you were used to. Tires for racing have lower tread depth to avoid this.

Check the torque of the lug nuts. Incorrect torque can cause this.

If all the above is done, switch the tires from front to back. If the handling changes, then there is a significant difference between the tires. It's always best to put on four tires because the same model of tire made at a different date can have different characteristics. Tires are a lot like wallpaper in this respect.

New tires always have higher rolling resistance than tires that are almost ready for replacement. This is to be expected. A 50 Wh/mi difference is within the normal range (in my opinion).

They shouldn't be "scary unstable" though. My first guess would be improper torque, and the second would be tire differences.
 

pdx4s

Member
Jul 16, 2013
23
1
Portland, OR
I stood by the tech to confirm the torque settings , they used 130lb-ft. as they claimed were told to so with MS. I drove very conservative for the first 400mls. I'm tracking E/miles, temp. and PGE data daily now on my commute drive to check for trends. There is one additional variable, 7.0 installed 36hrs before installing the new (same model) tires so I hope the daily data tracking will provide some insight to this phenomena. Lower e/m at higher speed is what is strange and makes me believe that this is possible induced by the tires rolling resistance at higher speed.
 

scottm

Legacy account
Jun 13, 2014
3,070
2,236
Canada
Nobody asking the obvious questions, so I will


What are the dimensions of the tires in question, maybe they sold you the wrong width or wrong ratio (I'm pretty sure they sold you the right diameter :tongue:) but the rest of it is what?

and what rims (and their size) that are you running these tires on, on stock or aftermarket wheels?

and do you have a staggered or square setup?
 
Last edited:

siai47

Member
Jan 23, 2014
164
190
Deland, Fl.
Look up the subject of "Tramlining" on Google and see if some of the descriptions of it's effect feel like something your car is doing. I my case it was more noticeable when the car (and tires) were new then it is now. On certain road surfaces (especially with grooves in them) it almost feels like the car is driving on a icy surface and fishtailing a bit. There has been some discussion on this in other threads and the suspension settings on the model S are kind of a trade off between straight line stability and quick reaction of the vehicle in a turn. You can reduce tramlining with suspension adjustments (making the vehicle more stable) but give up some reaction time in a turn--at least that's what I got out of reading some of the posts.
 

James Anders

Member
Mar 13, 2014
892
608
Southampton, PA
I've been struggling to understand how an incorrect torque value on some of the wheels would cause unstable handling.

I guess if the lug nuts loosened and backed off their seats it would be possible but just an incorrect torque - say 80 vs 130? Sorry, I don't see it.
 

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