Tires: 6 bad Michelin Tires? Continued, michelin tires, car drift

Question
QUESTION: Hi Barry,
Since this service will not allow anymore follow up with this question, a new one with the link to the old one has been created.
http://en.allexperts.com/q/Tires-2359/2009/4/6-bad-Michelin-Tires.htm  (look for the responses under the main tires section as they have not appeared at the time this is written.

“Mike,
I do not think the problem is related to the tires.
Does the car drift now? Under what circumstances?
If not, then you are good to go.”

You have lost me, how can I be good to go?  Nothing has changed.  Yes, the car drifts to right.  Fist, these are directional tires as stated in the first message of the main question.  The only time the tires do not drift to right is when the RF directional tire is put on LF then it drifts to left but drifts a little slower (can not leave the tires in the wrong direction).  And it happens at 35mph or 60mph or 80mph.  It happens on all types of roads.  Most noticeable on concrete.  Most likely because most asphalt road around here are toped over concrete and are likely to have ruts.  

If you do not think it is the tires, then what do you think it is and why?
For my piece of mind, the dealer put the car back on the alignment rack and took a reading:
Second Reading:
http://i62.photobucket.com/albums/h104/GreenTennis/Tires/IMGP5662.jpg

First Reading:
http://i62.photobucket.com/albums/h104/GreenTennis/Tires/IMGP5658.jpg

Possible explanation for the drift not being as strong to the left:  Possible very slight crown in the road tested.   Caster and Camber are not adjustable.  Before these tires were put on the car, this did not happen.  These tires now have about 500 miles on them




ANSWER: Mike,

I need to think on this a while, plus I am traveling, so it's difficult to find the time to devote to this problem.

If I haven't posted a followup with a week, please post a followup question then.

Thanks

---------- FOLLOW-UP ----------

QUESTION: Hi Barry,
Have you thought of anything with the tires?  Michelin after talking to the Lexus dealer said they will put any Michelin tire on the car.  Lexus is confident the tires are the issue.  DT hopes they are right but does not think it is the case.  I sure hope the asymmetric Pilot PS2 tire resolves the issue.  Not near the tread life though.

I found this TSB from Mercedes Bends on the pervious model of tire (the non plus).  Must have been fairly common for them to issue a TSB.  Since you are in the business, is these incompatibility issues more common than the consumer is aware?     

“TSB P-40_10-43 - Michelin Pilot Sport A/S Tires Not Approved
On January 16, 2004 Mercedes Benz issues a Star Bulletin to all their dealers as follows:
________________________________________
SUBJECT: All Passenger Models
Michelin Pilot Sports A/S Tires

Please be advised that the Michelin Pilot Sport A/S (all season) is not an approved (nor certified) Mercedes-Benz tire for any Mercedes-Benz passenger vehicle. Use of the above mentioned tire can cause vehicle tracking issues which MBUSA will not attempt to correct. MBUSA will not perform warranty wheel alignments on any subject vehicle which has any non-approved wheel/tire packages installed.
_______________________________________


then in June

Michelin ³Mercedes-Benz & Michelin Pilot Sport A/S² Technical Bulletin dated June, 2004. covers the slight modifications Michelin has made to selected sizes of the Pilot Sport A/S tire line to allow them to better complement medium and large sedans.

While the Pilot Sport A/S modifications are unlikely to change MBUSA¹s policy of not covering the costs associated with the diagnosis and correction of drivability problems of vehicles equipped with non-OE tires under warranty, test results have made Michelin very confident they have eliminated the cause of the subtle drifting experienced on a limited number of vehicles.”  

Answer
Mike,

The reason I wanted to think about this was that I wonder if P-RAT (Ply - Residual Aligning Torque) was playing a role here.  Many car manufacturers pay a lot of attention to this intrinsic tire property (I tend to think of it as a force - ply steer), but I always felt that conicity was the cause of drifts and pulls - at least those caused by tires.

I just threw a lot of terms out and I should explain them.

Conicity:  Root word "Cone".  It's a tire property that varies from tire to tire and is best described as a force pushing sideways (lateral direction).  The force can be pushing to the left or the right or the force could be zero - and the direction is oriented with the tire - that is remounting a tire with the other side out, changes the direction of the force.  Vehicles would tend to pull if a positive and a negative were mounted on the same axle.  

Ply steer:  Same idea as conicity but it is intrinsic to the tire and all tires of that type tend to have the same value.  It doesn't change direction when the tire is reversed on the rim.  You would think this would cause a drift or a pull, but it is hardly noticeable as the vehicle adapts a slight angle to the road (dog tracking)  In most of the world we drive on the right hand side, and the Ply Steer is towards the right causing the vehicle to push off the road.  Some tire manufacturers make special tires for countries that drive on the left hand side - but if the plysteer is small, it doesn't have much of an effect.

P-RAT:  Ply - Residual Aligning Torque.  Same as Ply steer, but expressed as a torque rather than a force.  It's the torque the vehicle sees.

So, when you posted the 2 bulletins about your tires, it kind of confirmed something.

Mercedes is unusual in that they want all their tires to have positive conicity - all pushing inwards.  Their cars use a large amount of camber - and so does yours.  Camber tends to cause a force on the tire which also pushes inwards. P-RAT tends to cancel this force on the right side and cause a slight drift to the right - which is why Mercedes wants all their tire to have positive conicity - all their vehicle will either drift to the right or slightly try to climb the crown of the road and be cancel by the slope.

However, most car manufacturers don't specify direction on conicity - only the range of values.  This can result in a situation where a tire with a very large P-Rat would cause a slight drift.

So that's what I think is going on.  There's something fundamentally built in to the tires that your car is sensitive to.  And no amount of fussing with tires is going to fix it unless you replace them.

So go back to Discount Tire and tell them you want something else.  Something in a different Michelin might work, but a different brand might be better.