High speed vibration

[kismetcapitan]

Am on a road trip to Chicago, and the car has got a vibration that kicks in at 80mph. It doesn't seem to get worse with increasing speed, but it's there. I went and toolkit a pit stop in a small town where I had the wheels balanced. They found the wheels to be pretty off...up to 75g. It lessened but did not eliminate the issue. Alignment? The car tracks straight and true. I noticed this before I did the spacers, but it was after I did the swaybars.

Any ideas?

[kismetcapitan]

ok, this is very odd...it only happens at 80-85mph. At 90mph it's smoothed out, and above and beyond that the ride is smooth as silk.

annoying as I tend to set my cruise control at 85...

[Brav]

I have a similar issue, lower speed. Most likely worn control arm bushings.

[kismetcapitan]

I would LOVE to replace all of those mushy suspension link bushings with pillowball joints, but sadly none are available :(

[SzymekCRX]

I'd go and check out rims. One of the front wheels could be unbalanced.

[kilian tuning]

ive recently straightened my wheels and balanced but it didnt solve my vibrations, so i have them balanced again (which needed again some weights....) and it was gone...maybe let them balance again...:) never a dull moment with a rs6 :)the vibration started at around 100km/h

[4everRS]

I agree with Brav that a lot of odd vibration issues seem to be solved with new control arms/bushings. You might also get under it and check for play in the axel itself. Usually those CV's will make noise if bad, but they could be at a point where they are just staring to go. Just a thought. Also, I think that there has been reports (I think Max) that said he had this issue and after new wheel bearings it was gone.

[kismetcapitan]

I'd love for it to be simple, but I'm going to put my money (literally) on bearings. How much does a set of new bearings cost installed?

[JSRS6]

They run about 100/each. Depending on how the shop does it, it could take anywhere from 1-2 hours per side. At least that's what they will charge. You could do it yourself fairly easily. If you were gonna wait.

[kismetcapitan]

after doing some research, I'm going to try balancing the wheels again at a shop equipped with a Hunter Road Force balancer and check the alignment.

Otherwise (since it feels like it's coming from the front), I'll have to start in on control arms, bushings, and hubs.

[Brav]

I am dealing with same issues.. even swapped wheels. i have all new control arms. havent been able to get to bearings yet... :/

[DonS]

I have a minor vibration that started after installing new brake rotors in the rear. For me the vibration is felt most at 45-60. I'm going to try my old rotors when I have a chance.

I hope you find your issue fast and cheap.

[ThrillHouse]

Over simplifying but an easy/cheap check; I had a similar issue that kept coming back in another car. Turned out to be one tire that would be a few pounds lower pressure than the rest.

[kismetcapitan]

Well, the solution is easy but not particularly cheap. One of the tires has two fat blisters on the sidewall. Will need to replace two out of the four tires unfortunately.

[JSRS6]

How old are the tires?

[Brav]

Those blisters are usually from smashing into a rough pothole or something.

[kismetcapitan]

not particularly old; they've got 8/32 tread depth left.

I just ordered 2 Hankook Ventus Evos; here's a question and is my math correct?

The Continental Extremes are listed as having a 26" diameter, and 11/32 tread depth. So with 8/32 left, that's 6/32 of wear off the diameter, so it should be now 25.675"
The Hankooks are also listed as having a 26" diameter (although how precise? Different tire brands and makes are always slightly off), so 25.675/26 = 98.75%.

Isn't the tolerance for the quattro system a 4% diameter discrepancy? So with about 1.25%, I should be ok? Or am I missing something big here??

btw, do the rears wear faster than the front? Two of the tires had 7/32 depth, and two had 8/32, but they forgot which went where...(wtf?)

[JSRS6]

MOST tires come new at 10/32, as you likely know. There are definitely differences between maufacturers. If i were you, considering the relative newness of the tires, i would hold either the place you bought the car from or conti to the manufacturer warranty, which should cover sidewall blisters. Research that warranty. You shouldnt be out of pocket for those tires.

As for the quattro tolerances, it is 4/32 between front l/r, as well as between rear l/r and front avg and rear avg. So your fronts and rears should be within 4/32 of each other , and the average of front and rear depth should be within 4/32.

[JSRS6]

My rears usually wear faster than my fronts, partially due to the center diff bias, but also cause i like to hang the tail out sometimes when weather permits. :burnout:

[JSRS6]

ok, this is very odd...it only happens at 80-85mph. At 90mph it's smoothed out, and above and beyond that the ride is smooth as silk.

annoying as I tend to set my cruise control at 85...

I had the EXACT same issue. We shall see tomorrow if 4 new Michelin Pilot Sport SuperSports help at all...:revs:

[kismetcapitan]

is that 4/32 as measured with a gauge, or 4/32 total (meaning 2/32 on a tread gauge since to get the diameter difference you've got to multiply that by 2)?

I suppose if I wanted to be REALLY particular, I could get the Hankooks shaved down to 8/32...

[JSRS6]

With a gauge. Dont shave them. I never could get over that. Buy new tires and wear them down? No one local to me does that anyway. Tire rack does it, but you have to get the tires through them. They cant receive shipments. If you are that worried about it, pt the worn tires on the front, and the new ones on the rear; theyll get even soon enough. If at all possible though, dont mix and match tires. Not only do you have to worry about the manufacturers claimed overall diameter, but different tires=different handling, different road noise, different grip. And of course, it is an RS 6.

[kismetcapitan]

I did order through Tire Rack, and unfortunately I elected to mix tires. It's just a waste to throw out three perfectly good Continentals; one is bad enough. And I want to shift my shoes to Hankooks; I'm well familiar with the K12 Evo, and have spent years bemoaning how expensive they are (they run about $300 for a 255 size in Korea) and how the Korean domestic market was getting screwed to support low prices overseas....so now that I'm back home, well, they're good tires, but on principle it's time to start cashing in on the ridiculously low price.

Top-range Kumhos and Hankooks aren't cheaply made; they're subsidized by buyers in certain other markets, particularly Korea, so that they can be sold around cost on the US retail market.

[kismetcapitan]

solved. A meticulous alignment plus cross-rotating the fronts finally got rid of it and the car is smooth as butter now :)

[SzymekCRX]

solved. A meticulous alignment plus cross-rotating the fronts finally got rid of it and the car is smooth as butter now :)

What do You mean by cross-rotating the fronts ? Toe alignment ?

[aussie rs6]

Well, the solution is easy but not particularly cheap. One of the tires has two fat blisters on the sidewall. Will need to replace two out of the four tires unfortunately.

from my experience, if the blisters are on the inside of the front tyres, mine were caused by inner sidewall hitting 'old knobbly' under extreme deflections -potholes, er kerbs. Old knobbly has been ground off and not experienced any more blister problems. This is a common problem running 19" eurospec rims and tyres -see http://forum.rs246.com/viewtopic.php?f=2&t=89329&hilit=knobbly&start=30

It may also happen with 18" rims and tyres under extreme deflections of the side wall, but perhaps not as likely.

:addict::addict::addict:

[kismetcapitan]

I think cross-rotating was tried, two tires were replaced, and the car simply aligned....by an indie mechanic who is very familiar with Audi S models - this is his first RS but the differences are, in terms of alignment, inconsequential.