DK570

A little more than a week ago I finally decided it was time to put the PZero Rosso's away, and mount new Blizzaks for winter. (Please don't argue I should have done it sooner, it's been 40 degrees and sunny in WI this winter) Despite being old (~6 year front, ~3 year rear) the C4 drove well with the Pirellis. The dealer mounted and balanced the Blizzaks on my stock 18" Carrera II wheels, and did an alignment. The service was good, and was happy to finally get an alignment done, I could tell the front was just a touch off.

Anyways, enough back story. I drive home not exceeding 40 or 45 mph and everything seems fine. At home I look at the service ticket more closely, and notice it says that "both right wheels have flat spot, may cause vibration." I think it's odd that they say "wheel" and not "tire", but I brush it off figuring I didn't notice anything on the way home. Next day I get on the freeway, and at about 65 mph the whole car starts vibrating. I wasn't sure if it was a resonance thing, so I got up to about 80, and the vibrations kept getting worse and were even visible by looking at the steering wheel. Since then, I've done almost 500 miles and it still vibrates at speeds above 65 mph.

What's going on? Do my new tires have flat spots? Did the dealer not balance them correctly? I doubt my wheels have flat spots, since they drove fine with the Pirellis, and Al tends to crack, not bend like steel. I thought that new tires a. should not have flat spots and b. if they did should wear round after nearly 500 mi. I would like some opinions before I go back to the dealer and tell them they need to be rebalanced. I expect their story will be that a weight fell off.

If you made it through all that text, thanks in advance. Plus a pic from fall, since I don't like threads w/o pics.

9964runner

worth a phone call to clear up the "flat spot " question. The vibration is would say is a balance issue, if the steering wheel is vibrating, probably a tire on the front.

Pac996

I'll try on the exotic side of possible cause.
Thought I heard traction management is on all the time.
Maybe tire sizes are setting off the traction management causing the braking to pulse.
Oh well, hatever it is its not as bad as the too big of a picture making reading your story near impossible without making work out of it.

Barn996

I would revisit the dealer, have them go with you for a test drive and try to get them to rectify the problem.

awrryan

Likely a balance issue. I once had to take my car in several times to have a dealer in south Florida balance the tires properly so that there was no vibration at highway speed despite its insistence that they were properly balanced. Make sure the tires are balanced using road force variation.

C4CRNA

Maybe they dropped the wheels when working on them and created the "flat spot".

DK570

Good thought on the PSM, but I turned it off today, and no difference. Sorry about the big pic, I don't know how to make them smaller. Looks like I'll have to get the dealer to look at the balancing again.

Divot

By dealer do you mean tire dealer or Porsche dealership?

You should load balance the tires. I had new tires installed and "balanced" by a tire dealer and had the same symptoms. Took it to my indy and he load balanced. Problem solved.

OGWGFIW

This website has a search function to find facilities that can load or road force balance. This is the only way I'll do my balancing going forward.

http://www.gsp9700.com/

Byprodriver

In addition to this & in view of the fact that the only thing that changed was the tires & the balancing it sounds like you have slightly bent wheels & need to insure the balancing includes the following method: There are two main causes of vibration in your vehicle. If it is speed dependent, increasing as your speed increases, and becoming especially noticeable around 40-45 mph, it is most likely a balance-related vibration. The second possible cause of vibration is that the tire and the wheel assemble isn't exactly round. When the high spots on the tire and the wheel match to each other, it doubles the amount of runout , or "hop." If there is a hop the vibration will not end when you rebalance your tires. A hop can often be fixed by simply loosening the tire on the wheel and turning it 180 degrees, reinflating the tire after relubricating the bead. If the problem persists, rotate the tire another 90 degrees, and again 180 degrees if there is still vibration. Doing this allows for the high spot to be tried at each quarter of the wheel, and at one of the points, the tire should be round. From here, rebalance the tire and test drive to check for remaining vibration. If you still feel it, the problem is either in the tire itself of elsewhere in the vehicle.

cardsrule

Make sure you didn't lose a wheel weight....It happens more than you think

DK570

I went to the dealer to re-balance, vibrations are now gone!

street rod

Good to hear you found the issue.

Hurdigurdiman

You should have been back at that dealer within an hour of you discovering the fault. No telling what damage you could have done to the steering driving another 500 miles hoping it would simply 'Go away'... Anyway that said... glad you sorted it out.