Bad vibrations

[Mitchell Segal]

Don't know if this is the cause of your vibrations, but I can tell you my
experience.  I have an '01 A4T w/ Audit 17" mags that came with the Sport
package that year.  

When it was time to change out the Summer tires last year, my mechanic
friend who was installing them called me over to the balancing machine.  He
spun the tire up and openned the lid to show me, that everyone of my mags
had a bad dent in the inner rim area, or was deformed and out of round in
some way, yet the outter rim looked just fine.  We would have never noticed
it if he hadn't been watching the tire spinning in the machine (you normally
don't see it, because as soon as you lift the cover, the machine stops the
wheel)

Now, I wouldn't call the roads up here in Quebec perfect by any standard,
but I make a concerted effort to avoid all potholes and such, so it
surprised me how bad the rims were.  I can only surmise that because of the
design (the spokes are all flush with the outer rim) that there is
insufficient support for this wide mag, such that the inner ring is much
weaker, when it comes to impact damage.  That, plus the 225/45-17 provides
very little in the way of tire sidewall to absorb large impacts, so the
inner rim takes most of the hit.  My guess is the factory rims are a little
on the weak side when it comes to this type of strength, coupled with the
very low sidewall tires, can easily cause dents in the rims to occur.  Hard
to believe, since the German TUV safety testing is one of the best, that
this design flaw can get through.

As soon as I had the new tires installed on these rims, I immediately
noticed vibrations at certain speeds.  This went on for the first few
months, until I guess the new tires developed a wear pattern to compensate
for the out of round rims, because now I barely feel it.

So my suggestion to you is, did you recently change your tires on the car?
If you can, I would try taking the rims off and spinning it on the balancing
machine, watching carefully for runout/dents in the rims.  If this is too
much trouble, you can try to do it at home with a friend.  Put the car on
jackstands, have a friend spin a wheel by hand as best they can, while
you're underneath the car.  You can usually see or feel the inner rim while
it spins slowly, and you will know right away if it's perfectly round, or if
there's a problem.  Some of mine were so bad you could see the dent in the
inner rim just by looking at it when you took it off the car (must have been
some pothole to cause that one).

Hope this helps (or not, as it's around $150 to straighten/true a rim, for
each mag).

Mitchell Segal


>Date: Thu, 20 Oct 2005 15:58:53 -0700
>From: Michael McLaughlin <mcloffs at mac.com>
>Subject: Bad vibrations
>To: quattro at audifans.com
>Message-ID: <28ad200de76f8261629cb51b47660dfd at mac.com>
>Content-Type: text/plain; charset=US-ASCII; format=flowed
>
>My '99 A4 is in the shop for a vibration. I initially thought it was a 
>wheel bearing (the symptoms were similar to the one on the other side 
>that was replaced earlier this year) but I just got off the phone with 
>my mechanic, who said they're not sure it's the bearing and don't 
>really want to replace it if they're not sure that's the problem. His 
>advice is to bring it back when it's worse and therefore easier to 
>diagnose.
>
>Here are the symptoms. There's a vibration up to about 25 mph, where it 
>more or less goes away. Above 25 and below 65, the vibration is very 
>slight -- if there's no one in the passenger seat it'll vibrate a bit, 
>but that's about it. Above 65 mph, it comes back with a vengeance -- 
>when passing on the highway the car shakes pretty badly. In hindsight 
>it doesn't change when turning like the other bearing did, and it's not 
>nearly as noisy, so I think my mechanic may be right that it's not the 
>bearing.  The one thing that made me think bearing is that I've been 
>getting some odd tire wear that looked like the odd tire wear I got 
>when the other bearing went bad.
>
>In the meantime, any ideas on what other possible causes might be? The 
>car has been aligned recently.
>
>Thanks,
>Mike