Shaking at around 85 mph
 

When the car starts to shake a little around 85mph what could be the cause, Tires are not balanced? Alignment not correct? Please advise

It could be either one of those 2 you just mentioned. Also could be a wheel bearing issue. Hard to tell. Better to just get a free estimate from your machanic. Maybe they can pin point it for you. I would start with the wheels being balanced properly first and then move onto the alignment next and finally the wheel bearing but only if the first 2 did not fix the problem. Those would be in order of cost from low to highest. :cheers:

it most likley is a wheel balance/bent wheel issue.
bearings will usually make noise at all speeds, increasing with speed.

You may also have a bent wheel, if you take them in for a spin balance they can tell you..

Read the TriGem thread and stop going over 85! Kidding. I couldn't resist.

Control arm bushings can also do this. How many miles on the car?

ONLY after 85mph?

Free quick checks; missing wheel weights, foreign debris stuck inside the rim, bent rim, tire tread/belt separation, loose lug nuts. (granted this should show up before 85)

Take it in have it checked out, balance, wheels, bearings, suspension, and steering components/alignment...possible driveline component

oh, forgot...front or rear?

:cheers:

Could be lose suspension component, but I bet it's lose Ball joint(s). How many miles on the car?

53000 miles on the car, I just bought it, so i know nothing about it

I've had a vibration issue that wouldn't go away, put on aftermarket wheels and vibration was still there. Lowered the car with new struts, eibach springs, and an alignment afterwards on a digital hunter machine and the vibration was still there. Had the wheels religiously balanced once every 3 months and each time the vibration was still there.

So I got fed up one day and decided to do a full inspection, all suspension components looked straight and true. All bushings didn't show signs of cracks. I was stumped until I jacked up the rear end and put it on jack stands then started the car and drove it up to 85 mph while the rear was on jackstands and the vibration was there. It ended up being my axles. So you're problem may vary, I would go with the routine maintenance stuff like alignment and wheel balancing (dynamic only!) and this is usually the source of vibration a large majority of the time.

Guess working at bridgestone has its perks because i have access to all the alignment, lifts, and balancing machines.

If it is a suspension related issue, try some simple diagnostics...
Use the 'wiggle' method to check if your tie rods and ball joints are fine. Jack up a wheel and wiggle it horizontally and vertically to see if there is any play, if there is play in the wiggle horizontally it could be a bushing or tie rod, if there is any play vertically then it could be a ball joint. Hope that helps.

Have the car checked out by a Porsche tech, doesnt have to be the dealership but get her checked out. Everyone could post their opinions on the thread but nobody knows for sure until someone verifies the info manually and visually.

Something is out of balance, or worn...

In this order, this is what I would check:

Wheel balance (check for lost weights, bent rims, abnormal wear on the tires)
Alignment
Tie Rods
Suspension (bushings)
Wheel bearings