Need a little help.. There is a vibration that starts at exactly 88 mph. Goes away at about 130mph. I know it's from the rear as my steering wheel is rock solid while it occurs but I really feel it in my seat. I've had the wheels rebalanced multiple times and road force balanced at an Indy.. Took to porsche after it persisted and they rebalanced them. Still there. What are your thoughts. Bad tire? Wheel bearing? I don't think its a bent rim or it would have been hard to balance and porsche would have noticed it. Even told them to make sure wheels weren't bent and they said they weren't. At a loss

 

Also I don't have wheel spacers

 

Is this a winding constant vibration or shaking on and off (quickly?)


My bad bearings situations in the past caused more noise than cabin vibration.


Balance issues only get worse with speed but, they also get more pronounced.


How is the car at 87mph?

 

No noise.. Its gets worse the faster I go over 88 but then go away.. Maybe they don't go away but just don't feel it at 130? Not sure.. But at 87 it's fine as soon as I hit 88 it's like a flip of a switch every time. Constant vibration.

 

Have you checked for worn mounts/bushings, axles etc?

 

Could it be as simple as this!

 

funny engine guy! Would be nice if you could switch wheels just to be sure they aren't problem.

 

Sounds like a bad belt in one of the rear tires. The wheels will balance fine on a road force machine but not necessarily show a bad belt. I had the exact same problem with mine over 80 miles an hour, the car felt very strange in the seat of my pants almost uncontrollable. Porsche decided to put new tires all way around problem solved. This was on a brand new car that's sat at the dealer for about a year.

 

I had the same issue, it ended being a bad tire. I agree with wreck111 with how it will balance and still vibrate.

 

Check the tire pressures constantly

I have Toyo R888s and the psi variations with even minor temp changes is amazing.... In winter 35F, I set them to a warm (20 miles warm up) = 32/35

On the 1st warm day above 50F I adjusted them down so they would be the same psi at 50F... yesterday with temps in the 70F range I measured the temps and they were all over the place

F right = 34 psi F left = 33.5 psi
B right = 39 psi B left = 37.5 psi

Car was snaky, really horrid above 100 mph... I adjusted all back to 32/35 psi.

Also, I drive with PSM off all the time... I get some whine and a lot of PSm interference which causes some really weird vibrations as our roads here are very rough and bumpy

 

My buddy that's a porsche tech said the same thing. He thinks it's a bad belt on tire.. Tires were replaced before I purchased it from my buddy but sadly the car was stored for the winter and I am just starting to notice it.

 

I have over 10 cars that I store 3 other Porsches I always pump the tires up to the max on the sidewall. 50-60 pounds when in storage. Seldom have a problem when I do this. Just make sure you reduce back to normal after you pull it out. I always drive it a few yards then reduce pressures. I also coat every metal part with WD40 including the brakes calipers and engine. Old boaters trick. This is done after a very detailed cleaning.

If you have a bad balance the tire will vibrate at set speeds, example:
40/80/160

It might be less at 40 than 80 though. With a bad belt it could be just one speed. Easy way to check, take a set of wheels and tires from a friends car and try it.

 

I read the OP and was going to ask about your Flux Capacitor's charge. LOL!

 

I was told my vibration after road force balancing was a wheel slightly untrue at the hub. Need to check that too.

 

My first guess was a broken belt in tire but thought that problem no longer occurred see from responses it still does.