Tires: Accord cupping tires, bf goodrich, negative camber

Question
Hello, I have a 2002 Accord V6.  The OEM tires were V rated Michelin MXV4.  I have experienced uneven wear of any other tire that I have put on other than the OEM tire.  First I put on the BF Goodrich Traction T/A V rated directional.  They started cupping after 20,000Kms.  Then I put the MXV4s back on with no cupping over the life of the tire.  Lately I've put on  Continental Extreme Contacts V rated directional and they wearing again unevenly in the inner edge.  In all cases I had the car aligned before the new tires went on.  My tire dealer said that Continental won't cover it under warranty.  My question is what is causing this?  Some tire shops tell me it's the negative camber on the Accord (that doesn't explain why the MXV4s don't cup), some shops tell me it's the alignment, toe in and the latest dealer who sold me the Continentals is saying it's probably the directional tires that cause this.  Who do I believe and why do the MXV4s work well but any other tire won't. I've researched this everywhere and can't find anything.  Your help or suggestions would be greatly appreciated.  Thanks in advance.

Answer
Joseph,

It is alignment - and the sensitivity of the tire to misalignment.

Alignment is not a case of "OK / Not OK".  It's a matter of degree.  My experience is that alignments must be within the inner half of the tolerance in order to avoid tire wear problems.  This is something that most folks doing alignments are clueless about - So "In Spec" is good enough for them.  This is just not true 100% of the time.

If I have this right you have gone through 4 sets of tires - MXV4, Traction T/A, MXV4, Extremes.  That should mean you have over 100,000 miles on the vehicle.  If you are under this value, then we have to consider that the type of driving that you do is affecting the result.

You should also be aware that tires are compromises and tires with high traction tread designs tend to be more prone to irregular wear.  The less aggressive the tread design, the better the resistance, but the worse the wet and snow traction.  Both the Extreme and the Traction T/A's are much more aggressive than the MXV4.

From the sounds of it, you have excessive toe out, with perhaps excessive negative camber.  I can't discount the possibility that spirited driving may also be a factor here.  Spirited driving reduces the amount of "Akerman" needed.  

Akerman?  When you turn the steering wheel, the front tires don't turn the same amount.  The tires on the inside of the turn have to turn more than the tires on the outside of the turn.  The difference is called "Akerman".  However, the faster a car goes around a corner, the less Akerman is needed - with the result that the inside tire (and since the weight is transferred to the outside turning a turn, this is also the more unloaded tire) gets dragged around the corner, rather than tracking.  Because of the suspension, that tire is only contacting the road surface on the inside shoulder during this turning motion - and the result is shoulder wear and irregular wear.

As you can tell this is a complex issue and the answer isn't straight forward.  Hopefully I've given you enough to think about so you can make a better informed decision.