QuestionQUESTION: I have a 2008 Toyota Sienna LE mini van. I rotate tires every 5,000 miles. At each rotation, no irregular wear was detected. After the 20,000 mile rotation, the tires began making a cupping sound. I first took the van to a Toyota dealer and was informed it needed alignment and balance. Next, I went to an independent repair facility for a second opinion; they found the alignment, balance, and road force were within specifications. I then went to another Toyata dealer for an alignment check; I have their print out that also shows the van is not out of alignment. What must be done to fix the cupping problem?
ANSWER: Bob,
I am of the opinion that published alignment tolerances - not the target value, but the allowable deviation from the target value - are too wide by half.
So even though a vehicle is "In Spec", I don't think it means the vehicle is "OK". Look closely at the toe and perhaps the camber. I think you'll find that the values are not within the inner half of the spec.
---------- FOLLOW-UP ----------
QUESTION: Barry,
Wow! Thank you for the fast reply! A retired mechanical engineer told me that on rear drive cars, toe in is to compensate for the wear on the inside of the tread caused during braking. He also said front drive cars are towed out slightly, because of the outside of the tread wearing from the tires pulling inward as they pull the car. This reasoning seems to coinside with my van specs which have the minus target for the front toe and a plus target for the rear toe. I have read too that much positive toe increases wear on the outside of the tread. Another mechanic recommends positive toe on the front to correct the problem. Do you think changing the front toe from minus to plus will help or cause accelerated wear on the outside of the tread?
ANSWER: Bob,
I think the vehicle engineers are smart enough to have figured out what the proper TARGET is for toe. I would ignore any advice from any source other than a vehicle engineer.
I know what you are thinking! Barry is NOT a vehicle engineer so why is he stating that the TOLERANCE is too wide. Well, the tolerances are set by manufacturing engineers and not the design engineers (although both might be considered vehicle engineers). I think if you asked a vehicle design engineer, he would say I am right about the tolerance. Not to mention I have lots of experience looking at worn tires and I have no issue with the target value!
---------- FOLLOW-UP ----------
QUESTION: Barry,
Thanks. I fully agree with you about the target value; which happens to coincide with what the mechanical engineer told me.
I have another question. Prior to the 2008 Sienna, I have had over 20 different automobiles. They were all driven at least 50,000 miles; many were driven well over 100,000 miles. Tires were seldom rotated. Some had alignment and balance problems. None of these cars including those with alignment and balance problems had tire cupping problems, except for the early Geo Metro and the 2002 Acura. When I asked Acura and Toyota people to tell me what is causing the cupping, their first answer was lack of rotation. What is the rational for them saying lack of rotation causes cupping, given the fact I know of at least 18 automobiles that seldom had rotation and did not have cupping problems?
AnswerBob,
Just because a person is in a position where you would think he understands stuff, doesn't mean he actually does understands stuff. I would say that the Acura and Toyota people you talked to might be good at repairing and selling cars, but tires is pretty much an area where car people don't have much expertise.
AND the key to this discussion is that the owners manuals specify rotation so when that doesn't happen, they are off the hook - which the motivating factor behind their comments.
