Steering wheel vibration @ highway speeds

[greg0078]

2001 996 Carrera Cab, 6 speed manual trans.

The car has 20k miles on it but the tires are old, based off the tire code i think they are ~7 yrs old. The previous owner barely drove the car. They have a little tread left on them, but could really use new tires, i am trying to nurse them thru one more summer as this is a dry weather summer car only.

At highway speeds on smooth roads i notice a vibration in the steering wheel and seat, from ~70 -84 mph over 84 it seems to smooth out again. From 70 up it starts out slight and then gets worse until i can feel the vibration in the seat.

Is this a mechanical issue or tire/balancing issue?

[logray]

Certainly if the tires are worn or worn unevenly it can cause vibration.

Or tire pressure, road surface can contribute.

Then balance.

Then alignment.

[RatboneRanch]

If the tires are that worn, I wouldn't try to nurse any more miles out of them in a climate like NJ's. Even a summer-only car can get caught in a sudden rain shower, and fast cars on worn tires are dangerous in the wet.

[Carmon997S]

I had the same problem with my old Boxster but my tires were not very old. I had the alignment and balance checked and they were ok. The problem turned out to be 2 tires had flat spots because it sat on the dealership lot for a long time before I bought it. They could actually see the tire out of round when it was spinning on the balancing machine. It wasn't hurting the car but it was a bit annoying.

[greg0078]

i took the car to a local porsche only shop. It turns out all 4 wheels were out of balance, and all 4 tires have flat spots. They balanced the wheels as best they could and the vibration at high speeds has gone. What i did notice wa a slight vibration at lower speeds 30-40 mph. once i replace all 4 tires and balance i'm sure this will be resolved. At least i know the cause was bad tires

[Carmon997S]

Glad to hear that you found the problem and the tires were not new when it happened to you. My tires always flat spot a little because the car will sit for a month or more at times. I have only had one set that did not round back out after I got them hot. Hopefully it will not happen to you again. Happy motoring and enjoy the car. :)