How to determine if a wheel is bent

My E46 M3 vibrates moderately at highway speeds (> 60 MPH), but it can can only really be felt through the seat, and not through the steering wheel. My guess is that a wheel is bent (out of round) or bent from side-to-side. Is there any easy way to check this? I can't see anything awry just by looking at the wheels, aside from a little curb rash.

How much bend is too much? Is it fixable?

Thanks, Jeremy

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Good question! I've had several shops tell me that ALL of my wheels are bent, including the brand new one that I just purchased from the dealer a month ago, but I'm highly suspicious of their diagnosis. (it's not like it's drive off-road or anything) – Greg Mar 28 '11 at 12:44

You probably have a wheel out of balance and it's difficult to determine that without putting the tires on a balancer. One thing you could try would be to jack up the car and put pencil on a stationary object like a brick or a board move the pencil so it almost touches the wheel, spin the tire and look for the rim moving in and out in reference with the pencil. That's really only going to give you a starting point though because if you have movement it could be a bent hub or axle and may or may not be the source of vibration.

Here is a picture as an example, this is actually a gauge but you can get an idea doing it the way I decribed above

Again I think it's more likely to be wheel balance than anything else and would try that first.

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I'll give this a try this weekend. I have to get the car up on jacks for other maintenence work, so I'll do this at the same time. I have a micrometer gauge, so I'll try to see just how round the wheels really are. – JeremyP Mar 25 '11 at 12:41
FYI - The tires were worn out and also out of balance. A new set of tires fixed the vibration. – JeremyP Mar 17 '13 at 14:28

Does the vibration go away at a higher speed, like 70 or 75? If it vibrates at 60 but goes away at 70, it's probably out of balance like Larry said. If it is still present at any speed, it's probably a bigger issue like bent rim or axle, etc... It could also be a manufacturing defect in the tire, or an improperly mounted tire.

Here is a good article about diagnosing tire and wheel vibrations, including matching the high spot on the tire with the wheel, balance, and out-of-round situations.

Particularly with low-profile tires, as I imagine you have on your M3, the wheels can take a real beating that a higher profile tire would absorb. It's just made worse by the stiff sidewalls on high performance tires. A few years ago a friend bought a used car with aftermarket wheels and 35 series tires. We went for a ride in it and I remarked on the vibration, and it ended up being bent wheels.

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Bending a wheel actually takes an awful lot of effort, but even changing a tyre requires a wheel to be rebalanced. If it can only be felt through the seat at 60 then it is a very small imbalance, so get your local tyre shop to rebalance both back wheels (guessing it isn't the fronts as then you would feel it through the wheel)

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The roads in New England, or in my neck of Connecticut, in particular, are particular terrible. I have seen pot holes six inches deep that look like they could rip the wheels straight off of a car, so that's why I was thinking it could be a bent wheel. That being said, I agree that it could be in imbalanced wheel causing the issue. – JeremyP Mar 25 '11 at 12:39