tbaker17

We need to get more in depth on the subject of the threshold of 'acceptable' road force defects in tire/wheel balancing.

Tire manufacturing is imprecise, so a given amount of out of round is inevitable. Add to that our heavy cars, tight suspensions and wide tires, and its not surprising we have vibration problems.

The Hunter machine has the capability of printing out a report that tells you the amount of defect in each tire, measured in pounds.

Audi says 'in tolerance' is 'around' 20 lbs. Lexus, by the way, says 12.

The Hunter machine also tells the tech which tires to put on the front wheels, presumably the ones lowest/best matched in road force.

Its been pointed out that tech training on the Hunter machine may vary. Its also a business reality that a lot of shops wont spend the extra pita time to do a full work up.

Then, should say 1 tire show up borderline, who is going to pursue a fix? Technically, the tires are covered by Conti, not AoA. I presume there is some spec in the contract between the two, but we are unlikely to find out what it is.

It took nearly a dozen visits to the dealer, all the while the SM and tech are claiming they cant feel the vibration, and the balance was within spec. I finally made them show me the hard copy of the Hunter report, and presto, 3 tires under 12 lbs, the 4th at 22.

New set of tires 5k ago, all balance under 15, no detectable problem.

I suspect the Hunter machine can solve many of our problems, if it is used to its fullest capability.

reholcomb

I went to a local shop here in Rome GA. The guy said that 10 was the threshold. I had 3 that were around 5-7 and 1 was 25. The hunter machine said the best it could get it to was 22. It did. He put the bad tire on the front driver side and said to run the fronts at 40 psi. It has definitely helped but is still noticeable. My tires are Goodyear's and are notoriously noisy. I can hear the bad tire while driving, especially while braking.

Northern Ivy

Yes, the hunter machine is a great tool. And as far as I know AoA will pay a dealer for a standard balance, the dealer does not recieve additional funds for the full road force work up, and this take time, which means lost $$ for the dealer.

My car for one has been through multiple hunter full work ups, one with an actual rep from hunter. And the vibration is the same, brakes tires and wheels have been replaced.

I would tend to make a guess that A6 have two types of problems.

1st the standard bad tire, this should happen to AOA as offten as any other car maker (my dealer was great at not making me deal with conti). And these are the problems that the hunter machince can find, and fix (replace tire).

The problem that AoA wants to ignore is the "Characteristic of the Car" or "Road Vibration". In the minds of many this is an engineering defect, and AoA does not seem to care resolve outside of the Court Room.

Just my take, and I am not trying to whine of be viewed as a troll...

RobertV

Four sets of tires, 4 new rotors, two sets of wheels...still not luck.
I love this car, there is nothing out there that comes close, just want it fixed.

PaulW

You mention that the units are expressed in pounds. That doesn't make sense to me.

Residual imbalance is expressed in oz-in, gm-in, or gm-cm. 1 ounch inch of residual imbalance is equal to 1 ounch of weight one inch from the center of the hub. If you had 1/2 oz at 2 inches, that would also equal 1 oz-inch if you get my point.

When determining residual imbalance for a piece of rotating equipment the following equation is used:

U= (K) W/N

Where:

U = Residual imbalance in ounce-inches
K = K factor (the lower the number the better, if you use 1, you'll have almost no residual imbalance, only used for high speed rotational equipment such as boiler feed pumps and motors)
W = Weight of the wheel/tire unit in lbs
N = Rotational speed of the wheel in RPM

So for an A6, I'm assuming a 255/40/17 tire which has a circumferance of 78.6" (diameter of 25.6"), which means it travels 806 revolutions/mile. At 60 MPH, it takes one minute to travel a mile, so at that speed it travels 806 RPM.

Let's determine a balance standard for 90 MPH, where it will turn 1,209 RPM.

Assumption: Wheel/tire combo weighs 45 lbs.

Residual imbalance = (K) 45/1209

= 0.037 oz-in with a K factor of 1 (tightest balancing standard you'll ever see)

= 1.11 oz-in with a K factor of 30 (probably more realistic of what you might find)

= 2.22 oz-in with a K factor of 60

If it was 2.22 oz-in and the balance plane is at the inside of the rim, which is 8.5" away from the center of the hub (17"/2), then adding one weight of 0.26 oz would throw the residual imbalance to a standard of 60 W/N. That's a 7.4 gram weight! I will have to see what size weights are on my wheels/tires.

So now my question is, where do they get 10 lbs and 15 lbs for the Hunter machine?

Are you ready to fall asleep yet?

pw

mpuzach

If so, why don't they replace the tire?

reholcomb

It is 99 and maybe original tires. I bought the car a couple of months ago. In fact the tires are fairly worn and will need replaced by next summer. Bumping up the inflation pressure make a noticeable difference, which makes sense if it is a load force problem.

duodallas

The hunter uses the hub for centering, and if it is not centered relative the bolt holes, the Hunter GSP9700 is useless, like it was for me.

Chucking the old wheels with lighter ones that were round made my problem go away.