QuestionI have a Classic 2007 GMC Sierra extended cab with stock GMC 20" rims and Firestone tires. I have 15000 miles on my vehicle and now I have cupping on the front tires. I have my vehicle oil and tire rotation at my local WalMart Store. This would have been my 3rd rotation (every 5K miles), but they told me this time the front tires have cupping. I maintain the recommended tire pressure for gas mileage purposes.
Is this a problem with large heavy GM vehicles? I owned a 2002 Suburban before my truck and the front tires did the same thing on it???
Thx. Happy Thanksgiving.
Pls reply to jdayzd33@hotmail.com
AnswerJohn,
"Cupping" is a term that is commonly misused, where the term "irregular wear" would be more appropriate.
"Cupping" is a term that is a holdover from the bias tire's day where bad shocks and imbalanced tire and rim assemblies would cause isolated "scoops" out of the tread.
Todays radial tires don't really show this type of "scooping", and are relatively insensitive to imbalance and bad shocks - at least from a tire wear perspective.
Cause of "irregular wear"? Misalignment, aggravated by insufficient inflation pressure and insufficient tire rotation. I think we can rule out the rotation issue and the pressure issue.
That leaves misalignment. Most vehicle spec are also throwbacks to bias tire's day and are way too wide for radial tires. I recommend that alignment spec be within the inner half of the tolerance.
So get the alignment checked and insist that the alignment be within the inner half of the tolerance.
