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Highway Vibrations

I have a 2006 Subaru Legacy GT that has a noticable vibration I can see and feel through the steering wheel when traveling at highway speeds 55-75. What stumps me is that the vibration will last for about 30 seconds then disappear for a bit and come back. Over and over again. I don’t feel it in the brake pedal and it does not change based on rpm. I just had my tires rotated and brakes inspected with no apparent issues, any thoughts?

Did they rotate and balance? Or just rotate? Get them balanced and see. Could have a cord separating in a tire.

Just rotated. I’d be supprised if that were the case, they only have about 7k on them. It’s worth checking, thanks

Tire problems do happen regardless of age. In any case, start with having the basic balance checked. Various things can throw off the balance including lost wheel weights.

But you also need to have a good front end/alignment shop check out all of the front end parts - esp. things like tie rods and ball joints. Find your best local, tire/alignment/front end shop and use them. Avoid the corporate chain places.

What you probably have is irregular wear. Irregular wear is caused by misalignment and aggravated by insufficient inflation pressure and insufficient rotation practices.

My experience says that the published alignment tolerances are too wide. Not the target value, but the allowable deviation from that value. I think it ought to be half of what is published.

Put another way, the alignment should be within the inner half of the spec.

You should be aware that even vehicles that do not have a pull can be out of alignment. There are settings where one out of spec condition is offset by another out of spec condition ? typically camber vs toe.

So why does the vibration come and go? Neither tire has enough irregular wear to cause a vibration by itself. But because there is a little bit of difference in rolling diameter, the vibration of each tire is going in and out og phase with each other. This means the alignment is not too bad, but enough to cause a bit of irregular wear.