Tires: Michelin Tires on Chrysler minivan, michelin hydroedge, bridgestone tires

Question
QUESTION: We purchased 4 Michelin Harmony tires for our 2003 minivan in May 08, right after we noticed the van pulling to the left.  We had the van realignned and the van still pulled, we've had the tires rotated and still have a pull, we've had the cradled adjusted and still have a pull.  We took it back to the dealership and they went through the same steps and still the van pulled.  The dealership took the new tires off and put Bridgestone tires from a new van on ours and the van did not pull.  We went back to the tire dealer and had Michelin Hydroedge tires put on and the van still pulls.  Can our Minivan just not have Michelin tires or what other explanation is there for the tire pull?

ANSWER: Leon,

One last test.

Swap the front tires.  

If the pull changes, it's the tires.

If the pull doesn't change, it's the alignment.

If the pull disappears, then it's both.

There is a tire property called conicitiy (root word: cone) that causes a tire to pull in one direction more than the other.  All tires have it, the question is how stong is the conicity and which direction is it pull.  The only time it is a probllem is when you have a pair of tires (it only seems to affect the steering tires) that pull strongly in the same direction.  Pulling in opposite direction cancels the effect, and there is threshold below which the differences doesn't affect things.  It is possible that this set of Michelins have mismatched conicity.

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

QUESTION: The front tires were switched when the Harmony tires were on the vehicle with the pull still going to the left.  The HydroEdge tires that are on the van now are directional, so they would have to be remounted to switch sides.  We've taken the alignment printout to two different tire shops and both shops have said according to the alignment the van should not pull, yet it still does.

Answer
Leon,

So if the front tires were switched side to side and the pull didn't change, then it is the alignment, not the tires.

I'm afraid to tell you that the alignment shops you showed the printouts to have missed something.  So let's eliminate some obvious things.

First, does the pull only occur when you step on the brake - if so, then the problem is in the brakes.

If the pull only occurs on acceleration, then that is called torque steer and that is a characterisitic of FWD and that can not be fixed (without completely modifying the transimission / half shaft arrangement)

Does the pull occurs only on certain roads?  Road crown can have an affect on the way the pull occurs.

Are there any special circumstances where the pull does not occur - or vice versa - are there any special circumstances where the pull occurs?

Like I said, this has got to be alignment related - the test I mentioned in the previous post should have eliminated tires as the issue.