8 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
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YOUR RESEARCHPressure Test My Theory
Reported or suspected cause
wheel & tire assembly imbalance
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
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Discussions that report identifying a cause
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Reported cause
Most likely cause is Wheel & tire assembly imbalance.
Leading evidence: 'wheel & tire assembly imbalance' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'wheel & tire assembly imbalance' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check before this recently' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
Have recently replaced the fronts but the rears look okay in a visual inspection.
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Suspected cause
If your feeling it through the seat I would suspect rear wheel or tyres as a first.
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Discussions that contain suggestions
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Suggestion
Have you had either of them checked before this recently?
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Discussions that contain suggestions
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Suggestion
I have found when experimenting with tire inflation pressures just a few PSI over the recommended pressure causes a vibration that is so much like a balance problem that I can't tell them apart.
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Suggestion
(Whenever I get a car back with new tires I always test the balance at some "high" speed just to make sure the tech's balance job suffices for speeds above 65mph.)
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8 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 1 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261026T165820Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Today my son and I took the Porsche on a 300 mile road trip. To a Duke lacrosse game. When going 90 mph and above, I can feel a vibration coming from the rear. Nothing crazy but it's noticeable. At first, I thought it was related to my motor mount up grade to Rennline semi sold motor mounts. However, I don't believe they are the cause. When I put the car in neutral above 90 the vibration is still there. I can also run the RPMs up in a lower gear and don't have the vibration. Appears to be speed related and not RPM related. Next guess would be it's either tire or wheel balance related. Any other considerations?
Alignment has zero affect on vibrations. Non stock motor mounts always will. Most likely cause is Wheel & tire assembly imbalance. For a get it right the 1st time solution, & best possible balance you need to have the wheel/tire balanced on the car with a highspeed strobe balancer. Off the car spin balancers spin & balance @ 65mph or less. If the wheel bearings are worn they contribute to the issue.
If your feeling it through the seat I would suspect rear wheel or tyres as a first. Have you had either of them checked before this recently?
What's the age of you tyres also, could they have any flat spots (lock ups)
Do you have pot holes where you are that could damage a rim
O_Sr
I have Dunlop Direzza z2 s and they are about 2 years old. They were balanced last when mounted. They have a fair number of track days on them. Have recently replaced the fronts but the rears look okay in a visual inspection. Sounds like probably either tire or balance issue. Thanks for the input!
If you tell me the tires are worn say half way down I vote for tire imbalance. The word I get, and my experience with my Porsches has confirmed this, is as these tires wear they can go out of balance. The heavy areas of the tread can be worn away -- along with the lighter areas of the tread -- and this affects the tire's balance.
If you telll me the tires are pretty new have not experienced much wear it could still be tire balance.
One explanation is the tires were not balanced that well and you are noticing this for the first time. (Whenever I get a car back with new tires I always test the balance at some "high" speed just to make sure the tech's balance job suffices for speeds above 65mph.)
Another possible explanation is a tire has a defective belt and it has caused the tire's shape to change. A balance will help, at least appear to help, but as soon as the wheel is mounted back on the car and driven some the bad belt will have the tire acting up again.
Fortunately a tire with a bad belt is rare.
Be sure if the tires are uni-directional they are all mounted the correct direction. And make sure the tires are all correct, have the same specs. Same N numbers, speed rating, tread hardness, load rating, etc. Long shot but check the tire dates, too.
It is also possible a wheel is not mounted properly. If the wheel doesn't fit flush against the hub face, if the wheel does not center properly on the hub then then the wheel/tire will act like it is out of balance. It isn't much though or you would feel this imbalance at lower speeds.
There is another possible explanation: Tire inflation pressure is off. I have found when experimenting with tire inflation pressures just a few PSI over the recommended pressure causes a vibration that is so much like a balance problem that I can't tell them apart. Fortunately before wasting money on a tire balance job I had the presence of mind to reduce the tire pressure back down to where it should have been in the first place the vibration went away.
