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You are here: Experts > Autos > Auto Parts > Tires > Cupping Problem
Tires - Cupping Problem
Expert: Barry Smith - 11/5/2009
Question
QUESTION: 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!
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