Vibration at 85 mph

Hi guys, I hope you can help. I have had a vibration problem at 85 to 90 MPH since new (2003 996 cab) At 11,000 miles new tires, balanced 3 times by 3 different performance shops. All check fine. Dealer keeps saying the tires are out of balance as reason. I drive 125+ miles per day with 75 to 100 in excess of 85 (I-5 between San Diego and Orange County and I get passed by Moms in minivans) and my car does not feel planted or safe. I'm not sure what to turn to at this point. I have the stock set-up, Porsche 5 spoke light weights and bridgstone tires. What should I tell the dealer to look for as they seem unable to move off the tire balance problem? TIA Bruce (BTW This is my 3rd 996 with no prior problems at all!)

I know from experience that vibrations because of an wheel balance problem start around 50MHP...maybe it is a problem with the rear axel. I would aks the dealer to drive it while I am next to him and make him take it to 85Mhp and let him feel it. I had the vibration once when I made the dealer tighten the e-brake..but after 15 miles (on my way back to the dealer) it stopped.

This can really be an annoying problem which for some cars just won't go away permanently. I had the same problem on a Lexus. The vibration would begin at around 65 and go away around 75. I had one wheel replaced because it was slightly bent and then had all four wheels balanced. The problem went away for a couple of months but then came back. I took my car to the best tire/wheel Dealers in the area but the vibration would always recurr. After two years and four wheel balancings I gave up and sold the car.

That may be something of a generalization. My car came with new tires and a vibration that begin in the 80 MPH range .... no lower. Tire dealer said, "you need new tires or new wheels, these cannot be balanced". My indy mechanic made it smooth as glass. When I asked how, he replied, "I just balanced them properly".

I had a similar problem and I forget which tire balancer they used but there is a Hunter (I believe) balancer that can simulate high speeds. Maybe someone else can chime in with the model number. Anyway, after that, the vibration was gone.

You may have a tire out of round. I just pulled one the other day that was doing the same thing. it balanced just fine, but watching it on the balance machine as it spun, it was obvious that it was out of round. Swapped it with the spare, viola.....no more vibration. Tire Noise: alignment Vibration: balance or "round" Almost always......but there are some exceptions.

Here is a LINK The Hunter GSP9700

Thanks for the input. The tires were balanced on the Hunter equipment. On my drive up today, I paid close attention to the speeds at which the vibration occurs. Starts at 82 mph every time, goes away at 96 every time. I had my indy mech check the wheels/tires to be sure I didn't have anything bent or out of round. The last time I took my car in the service mgr drove the car with me in it to 85 + and continued to insist it was tire balancing. I'm at my wits end with the car and nobody seems to know what to look at next. Thanks for your replys, hopefully I can find the problem. Bruce

Can you determine from which portion of the car the vibration is emanating? Front or back? And could you also describe the vibration a bit more? Is it round or sharp feeling? High frequency or a slow throbbing? As someone mentioned above, it very well may be an axle. As many times as you have balanced the tires does not necessarily mean that it is not the problem. This may sound crazy, but see if the dealer will put 4 wheels on the car that run in perfect balance at those speeds on another car and see if you still get the vibration. If not, voila, problem solved. If so, then look at the axles. Smaller radii items that are slightly bent often do not raise their problematic heads until they are really spinning fast. Oh, one quick last thing....check your air pressure and make sure it is right. Try adjusting higher and lower.

On my Toyota SUV, I had a similar problem. I had put on new Bridgestone tires and it did not correct vibration. Dealer swore it was the tires. I returned the tires to Bridgestone (30 day guaranteed), and bought new tires from the Totota Dealer (same price too). They could not get rid of the vibration either. They ended up replacing all 4 wheel bearings and a shaft. ALL under warranty. This is not suggesting what your problem might be, but if you can get a decent price on tires from the dealer, either they eliminate the vibration or fix it under warranty. (barring bent rims).

I had a simiar issue on my 540i and it turned out the bushings needed to be replaced. ONce replaced it was smooth as can be.