GT3 Shaking

[Juanfer_GT3]

Hi,

I am the proud owner of a 997 GT3. She is just amazing and has provided endless hours of high speed fun, but above 120 mph I feel the steeringwheel shaking a bit too much. I used to have a 997 Carrera S and that car felt like a smooth jetfighter at 130+. I have taken her to do some wheel balancing, but it did not really help. Could it be the tires? I am using the Michellin cups and have 8000 miles on them. How long do these tires last?

Thanks a lot for any info.

[clord]

Hi Juanfer..... Congrats on your 997 GT3. As you know, tire balance and geometry is very important. Some balance jobs are better than others. Watch the balance tech and see if he sets his machine to read in grams, not, just ounces(the default is usually ounces and you have to enter a key sequence to switch it to grams). There are about 28 grams per ounce and the resolution can be better with the gram readout. Get it to zero grams in two planes. Are the tires round? Watch the circumference as they spin on the balance machine....look for 'lumps'. Are you using the stock wheels? After market wheels can add additional things to look out for, such as hub concentricity and proper wheel bolt seating (I've seen HRE wheels with the wrong size/shape bolt seats that would not stay tight). I've seen after market wheels that require a hub insert ring to fit a Porsche hub....and the ring comes out and concentricity becomes impossible. If all that is correct, a tire could still be defective such that it's shape changes at speed and makes for vibrations. Lastly, you might check the brake rotors for flatness and shock/damper health. Let us know what you find out.

[george996]

I recently spent a lot of time and money to resolve the same problem. One of my rims was slightly bent. Had the rim straightened but the problem wasn’t eliminated. From driving my PS2’s for a few thousand on the bent rim they needed to be shaved. Can’t tell where you are located but I took my car to Nate Jones Tire in Signal Hill, CA and he shaved the tired and did an “on car blancing”. Problem resolved.

[White987S]

I would suspect tires too. 8,000 miles on Michellin Cups is a lot of miles.

[john.jay@hotmail.com]

Hi,

I am the proud owner of a 997 GT3. She is just amazing and has provided endless hours of high speed fun, but above 120 mph I feel the steeringwheel shaking a bit too much. I used to have a 997 Carrera S and that car felt like a smooth jetfighter at 130+. I have taken her to do some wheel balancing, but it did not really help. Could it be the tires? I am using the Michellin cups and have 8000 miles on them. How long do these tires last?

Thanks a lot for any info.

8k mi. is way too much and likely the reason for the vibration. You may also have flat spotted one ( or more). You didn't mention if you'd tracked the car as well. If this is the case you're long over for some new rubber. Try the Corsas.

BTW your other quiry, look for the little yellow icon as you approach 8200 rpm. This will save you from getting into the soft limiter ( assume you over reved on the upshift....not really aproblem if it's infrequent. :)

[Juanfer_GT3]

I would suspect tires too. 8,000 miles on Michellin Cups is a lot of miles.

Thanks for the tip..will change tires inmmediatly

[Juanfer_GT3]

I have not tracked the car and it was silly to assume that the michellin cups would last longer. Thanks a lot

[White987S]

I think Michellin Cups have a treadwear rating of <100 compared to PS's that are about 200. FYI.