nickwh

Please help. I've had issues with vibration ever since I replaced the original tires last October (2010). I had some vibration before this and a slight steering wheel shimmy @ 55MPH, but nothing this bad. Everything is smooth until I go past 45MPH and then it gets worse with peaks around 55, 65, 75, etc. I had a front wheel straightened last winter by an on-site repair service. This helped for a while, but the overall vibration got worse. Finally I took it to a wheel repair specialist last month, turns out both front wheels were bent (the same one that was repaired earlier this year). Also, both rear tires are slightly out-of-round (Dunlop SP Sport Signatures, I cheaped out). So I paid to have the front wheels straightened and the rear tires geometrically balanced (Hunter Roadforce). This helped for a couple of weeks, but magically the vibration comes back worse than ever. So my questions are:

-Can straightened wheels go back to OOR due to aluminum "memory?"
-Can OOR tires cause steering wheel shimmy (thought only bent rims can do this)?
-Is there anything else on the car that could be causing these vibrations? Axle shafts, CV joints, bearings, etc.
-If not, should I just start over with new wheels and tires because anything less is futile?
-Any suggestions for an aftermarket wheel that has OEM specifications because I don't want to deal with suspension issues, wheel spacers, lug nuts not staying torqued, etc.
-Why do Dunlop tires suck (rhetorical)?
-Why are the OEM wheels so damn soft?

The car has 63K miles on it. What a huge PITA.

Thanks,
Nick

Just Me

First to your questions:

- Can straightened wheels go back to OOR due to aluminum "memory?"
--> no, but they are now weaker locally and can bend again
-Can OOR tires cause steering wheel shimmy (thought only bent rims can do this)?
--> of course - only the tire tread touches the road! Wheels just distort the tire!
-Is there anything else on the car that could be causing these vibrations? Axle shafts, CV joints, bearings, etc.
--> center drive shaft, but i'd focus on the obvious - wheels and tires
-If not, should I just start over with new wheels and tires because anything less is futile?
--> most tire shops appear to be incompetent. I typically put wheels on a balancing machine and watch them spin. Amazing what you see. I also find Hunter RFB machines to be a crutch for people who dont like to spin tires and look; who don't like to find the high spot on the rim and counter-balance it to the high spot on the tire, and otherwise don't know good mounting and balancing practice. A conservative estimate says this is 99.9% of the high school dropouts mounting tires. So dont accept simple answers. They may be wrong.
-Any suggestions for an aftermarket wheel that has OEM specifications because I don't want to deal with suspension issues, wheel spacers, lug nuts not staying torqued, etc.
--> OEM is you best bet
-Why do Dunlop tires suck (rhetorical)?
--> do they? I love my wintersports
-Why are the OEM wheels so damn soft?
--> they are average. Stiff costs money since they must be forged

I'd flip the question around - why do we all demand 25-series tires on 21" wheels for the road, and then complain when they bend on a pothole? I moved my S6 from 255/40-17 to 245/50-16. Bling heresy. Problem solved.

Yes, loose suspension can magnify problems, but they originate in the wheel/tire system 99.x% of the time.

Grant

nickwh

Thanks for the reply by I take exception to this statement. I'm running stock 5-spoke wheels and tire size (235/45/17). This is "entry-level" low profile and not what I would consider bling. I had this same size on a Mustang GT and never had these issues (of course, that was RWD). I would never run anything bigger than an 18", especially in the northeast where the roads are horrible. I don't think it's unreasonable to expect a 17 inch stock alloy to be bend free running proper tire pressure, as long as you don't hit a curb or run over a pothole that bottoms out the car.

Even SUVs come from the factory with 20-inch wheels these days.

EDIT: Interesting that Tire Rack doesn't carry any 245/50R16 size tires.

Just Me

i had no idea what you were running. but you proved me right :-)

Note my comment is about the general trend, not that you were creating bling. But ill wager that fashion is the major reason Audi supplies so many cars with 17 rather than 16" wheels.

no, 17s are not bling. But the larger wheel with a smaller tire (compared to 16s) is still the root problem, whether we like it or not. A 235/45 tire, in my opinion, and experience, does not have the sidewall height and overall internal volume to adequately protect the rim. especially in a car that has 60% of its weight on the front wheels, and, under braking, maybe 80%. That makes a BIG difference.

I already told you that the 255/45-17s i had (larger than yours) would not protect the wheels. So i went to 16s.

All it takes is a small bend on the unsupported inside lip to create havok on these over-sensitive cars.

So, regardless of sensitivities, that is a very likely problem. You yourself said you've already straightened more than one wheel.

The C5 and your mustang are different cars, with different weight distributions, different offsets, and different tire sizes.

Your comments misconstrue, or simply miss, the fundamental technical issue here. Its not about a 16, 17, 18, 19 or 36" wheel. Its about the size of the tire and the height of the sidewall, in relationship to the weight and impact it must sustain.

G

Just Me

here's page after page of 245/50-16 at tirerack.com

I bought my original set there.

http://www.tirerack.com/tires/TireSe...50&diameter=16

Where's you get that idea?

nickwh

That's strange, didn't work when I searched that on tirerack.com previously.

Anyway, I'll consider your solution. I assume that size maintains the same tire width and overall height compared with the stock 235/45/17? Will an OEM Audi 16-inch rim clear the larger brake calipers on the 2.7T vs. a 3.0?

I'm looking at something like this:
http://www.finishlinewheels.com/AUDI...03/A-58753U20/

SloopJohnB@mac.com

There are OEM 16" rims that fit 4.2 A6s with HP2 calipers. I'm sure there's a 16" rim that will fit your 2.7T.

Just Me

So, take it with a grain of salt. I mostly used it to make a point.

That particular size does NOT maintain gearing or diameter - its + 2.7% if you do the math. That also makes it bigger and more protective. I('m fine with that.

Plus..... manufacturers mostly DONT make 235/50-16 which would be the size closer to OEM (225/50-16 is spot on). 225/50-16 fits nicely on a 7.5" wheel too.

Its also very hard to find 8 x 16 x -35 (the size you pretty much need for 245/50-16). So be forewarned.

What i might try is 245/45-17. 2 load ratings higher, and another 4.5mm (10 x .45) sidewall height. Every little but helps. And mostly be aware that we have fragile wheel/tire systems. that means avoid chuckholes, and when you can;t, be aware that it not "did i maybe bend my wheel?", but rather "i wonder how late the wheel straightening place is open?"

And finally, double check. Even places i trust tell me "oh, that little imperfection wont make a difference" or "they're all like that" ( may be true!). Wrong. It does on these cars.

I hope you get it straightened out (pun intended) i know how frustrating the chase can be. I'm just pointing out the truths no one ever seems to tell us.

G

SloopJohnB@mac.com

One other thing...yes alloy wheels don't have 'memory' such that they'll go back to the bend, however, generally the wheel bends are cold straightened or impact straightened or best case heated up and straightened. These alloys tend to work-harden; they can be straightened either by impact or hydraulic with proper heat, but unless the entire wheel is heat treated or cryogenically stress relieved (and either process will destroy the paint and require refinishing) the straightened part is actually stronger but more brittle. If and when it gets hit hard enough it will bend again at a higher stress and it can break. Of course, it could have broke the first time it bent...the fact that it didn't just means the stress wasn't great enough.

Just Me

Quite a few. There are the OEM 4.2 wheels. Nearly any of the Ronals (RIP). Most must be et35. Former is 16 x 8, latter is 16 x 7.5.

G