Staggered setup causing jitter under acceleration

[kmikuta]

Hello everyone, just swapped on some different tires in the front for an autox event. I know quattro allows a very small window for rolling diameter difference. Front tires are Conti extreme contact DWS 225/40/18, rears are falken ziex _____. Continental tires are known to run a little large, and they have a little more tread depth than the falkens in the back. The rolling circumference difference is .7%, should it be causing as much shake as i'm feeling? It is only under acceleration, non existant during idle cruising or decel. Any insight on what could be causing this. I think I am definitely within safe range, i also have the 4:1 upgraded center diff if that changes anything

[james 408]

jitter? like what vibration? car wandering? in the steering? whole car? wheel spin associated? there a sound? where's it coming from?

when you swapped out tires/rims did it go away?
Did you forget to take off traction control?

It's a blown gasket.

[kmikuta]

Slow paced vibration that increases as rpm's do. You can feel it in the footwell, but hardly any sound. No wheel spin, doesnt affect steering, i would say that it seems like the center diff, but there was already a variation in tread depth between front's and rear's. Only thing that has changed is both front tires are 10mm more narrow, the rolling diameter/circumference is well within the safe range reccommended by audi

[james 408]

I'd try swapping back to your old setup - confirm it goes away. I suspect it's an unbalanced wheel or something of that nature. snap a vid would help know what you're dealing with.

[kmikuta]

I just swapped tires on the wheels, so i cant easily go back to the old setup without remounting and balancing my old tires. Took a video but the exhaust easily overtakes the slight noise. Im swapping them to the back, there's a chance that the new tires have a larger diameter. Im assuming the drivetrain would react better to the larger in the rear rather than the front

[LINDW4LL]

You're well within Audi's allowable "safe" tolerance- which is 3%, and even then I think that suggestion is with the health of the center differential in mind rather than being for drivability's sake. I've not heard anyone complain about a vibration resulting from a staggered setup.

Given that the differential likely has a lot of miles on it and internal parts do wear, in addition to the fact it was modified, I suppose it's possible that it's your cause; but not likely IMO.

[MacFady]

If it's jittery going straight, how much does that increase when doing a full lock turn? If it's the same than I wouldn't attribute it to your tires per say, as noted above you're well within range. When you say in the OP "Front tires are Conti extreme contact DWS 225/40/18, rears are falken ziex _____." are you saying the Falkens are also 225/40/18? Also noting you say it only happens under acceleration and no other driving situation makes me think not tires.

[seanf86]

I had what I thought to be bad tires and a vibration while accelerating, turned out to be a bad hangar bearing and seized u joint on my driveshaft.

[NOTORIOUS VR]

Sounds like the center/driveshaft bearing to me.

[audacity]

Sounds like the center/driveshaft bearing to me.

this

[julex]

post the exact sizes? Are they the same? I don't think they are since you jsut said that one is narrower than the other so maybe you think they are the same but they are not? Best way to compare is to simply compare wheels side by side and see if there is height difference.

[vavJETTAw36]

post the exact sizes? Are they the same? I don't think they are since you jsut said that one is narrower than the other so maybe you think they are the same but they are not? Best way to compare is to simply compare wheels side by side and see if there is height difference.

Don't matter. He fixed it.

[wbrunner23]

Don't matter. He fixed it.

When did he fix it? How did he fix it? I didn't read that - you got some insider information?

Either way tho, I think it does matter. We have too many threads that start with a problem and don't end with a resolution.

[kmikuta]

I rotated the tires which were in the front to the back, it pretty much went away. I also bumped up the smaller tires air pressure to 38 from 33 and that eliminated the rest of the noise. It was all tires, noting to do with drivetrain. I would have been feeling symptoms prior to the initial tire swap if something was wrong with either of the diffs, but the car drove really smooth under all driving conditions.

[NOTORIOUS VR]

Me me it makes no sense at all that swapping tires made an acceleration vibration/jiggle go away... but if that worked for you all the better.

[Nollywood]

My experience might be unrelated, but...

I ran 255/35x18's on 8.5"x18" wheels on the front of my old B5 Quattro, and 275/35x18's on 10"x18" wheels on the rear. It didn't vibrate, or make any noise. What did happen though, was every so often, the ride twitched. It felt like the rear stepped out, kind of like the rear subframe bushes were worn, causing a rear-steer condition. It was pretty random, and it made the handling unpredictable. This was with just 2.2% rolling difference front and rear.

I had a similar issue on my 2002 B6 3.0 Avant Quattro tip.

I can only imagine the torsen centre differential was varying the drive between the front and rear differentials, due to the difference in rolling diameter. I swapped back to the same size front and rear, and the handling went back to normal.

I won't run staggered on Quattro anymore, even with Audi's recommended max allowed percentage difference.

[MacDaddy]

I had something similar when turning, changed my center diff fluid and it went away, mind you im tip, afaik the manuals share the trans and center diff fluid. Maybe try changing the trans fluid if it hasnt been done recently, but it it doesnt make the sound during turning im inclined to beleive it may be something else.

[vavJETTAw36]

Were you running spacers? Any chance they were non-hubcentric type? That'll do it.