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Old 10-20-2005, 11:08 PM   #1
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wheel vibration problem

Ok, so i'm trying to help out my friend with this problem for the past few weeks, but still no 100% solution.

My friend just got some 19x8.5 and 19x10.5 wheels with 235/35/19 and 275/30/19 on his boxster. The wheel is hubcetric since it fits good on the hub. when we first install the wheel onto the car......the car has a very bad vibration from the steering wheel starting 45mph plus. our first solution was check the wheel balance on a better computer balancing machine. And the second thing we did was check the toe and camber of the car....since the stock size tire was 205/50/16 and 225/50/16.

after correcting the toe, camber and balance....80% of the vibration is gone....but still not perfect. I understand the wider tire will give it more road feel....but there are still some vibration from the steering wheel. Now the car seems like is driving on a rough surface all the time....and the vibration is mild but it gets worse as the speed increase. the vibration now starts from 85 plus....and once it hit 100mph...the whole car vibrate like a honda civic.

any idea? any suggust is welcome....thank you

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Old 10-21-2005, 07:20 AM   #2
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Hi,

Did you dynamically balance the Tire/Wheel? I don't mean Spin Balancing, I mean Dynamically on a computerised Hunter 9700 Series Balancer? I suspect you may have a bad tire, not at all uncommon.

Also, too little information. What are your offsets? Fr/RR? The wrong offset on the rear can cause the issue you're talking about.

Have your Scuff Radius and/or Ackerman Angle changed and was this compensated for? Upsetting these can affect the Caster which you do not mention.

Have you done both a Front and Rear alignment? What adjustments have you made to Factory Specs to allow for the changes in Wheel/Tire?

What you're trying to track down here can have many sources, even compounded ones. If you don't have the proper measuring tools, you're just Stabbing in the Dark.

In order to preserve the investment you've made in the new Rubber, I suggest you take the Car to a proper alignment shop, preferably one which does Race Setups and let them try to diagnose it. A long distance diagnosis on so obscure an issue is near impossible to make. Good Luck!

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Old 10-21-2005, 07:25 AM   #3
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Several ideas:

1-Slow down, you will save gas, speeding tickets, medical bills, insurance costs, reduce risk that you might injure or kill others, etc. A very good move indeed.

2-Revisit the rebalance with the best shop in your area. The front tires balance on the Box are VERY sensative.

3- In my experience, the larger the tires and more contract area you have on the Box the more you will feel the road inputs in the steering wheel.

4-Chat with someone expert to insure that the move to 19s was done perfectly. Frankly, if memory serves, Porsche does not recommend 19s on the 986 but I may be wrong here.

5-Reconsider a move back to 18s. These were designed for the car and certainly don't disappoint most of us here.

Last edited by Brucelee; 10-21-2005 at 09:22 AM.
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Old 10-21-2005, 09:11 AM   #4
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What's the mileage on the car?

There are so many things that can cause it. I'll start with the easy ones.

1) Clean all of the ABS sensors with brake cleaner. They can collect metallic dust from from the pads on the magnets over time and then they suddenly can't feel the wheel moving. They can freak out thinking the wheel is locking up since the speedo says 85mph and the sensor thinks the wheel is not moving. It starts to pulse to unlock the wheel and you feel vibration. When mine did this, it was over 80mph and as I went faster it got worse to the point where it was shaking really hard.

2) Out of round tire.

3) Worn A-arm bushings. Not a good one since you have to replace the whole arm. They don't sell the bushings separately.

4) Bad wheel bearing.

Just a few I can think of off-hand.
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Old 09-27-2006, 08:21 AM   #5
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My vibration was a real nightmare for 6 months.

My back tires was finished so I decided in the spring to get 2 Pzero. I got them installed and balanced on GForce machine. Since day number one I had a slight vibration around 75-80 mph. I went back for rebalancing and they were able to reduce the variation by repositionning the tires on rims.
Drove it for a month a nothing changed ...vibration was still there, since I thought that the tire have to be worn a bit a decided to be patient.
Decide to bring it to Porsche dealer, redid the balancing on GForce and still the vibration was there. The dealer decided to have a close look to all running mechanical pieces ( brake rotor, driveshaft etc....) nothing wrong found. I drove it another month and took it back to dealer and complained. They redid the balancing of the four wheels and they suggested to have the mags checked in a specialized place.
Had the 4 tires removed for mags and mags checked. No problem found despite the fact that I had to pay $$$$.
Went back to dealer and gave him the results of the mags inspection. At this point the vibration was a real headeach to the point that I stopped driving the car.
One evening while I was watching TV I decided to jack the car and invert the wheels position from left to side for the back and front tires.
Took it for a ride and TADAMMMMMMMMMMMM no vibration anymore, a real miracle with no explanations. I took the car to 130mph and it drives like a charm .....
Went back to the dealer seeking explanations and they gave the bull****************t lines about the fact that the car is built in a way that if you change wheels positions from original it may affect the handling and that probably the guy who installed the tires didn't respect the right positions bla, bla,bla......

Until today it's a real mystery but it's driving incredible nice and that's what it count.
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Old 09-27-2006, 08:52 AM   #6
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Do the wheels require spacers and if so - are they installed or installed properly?
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Old 09-27-2006, 09:03 AM   #7
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Old thread but will give my $.02 anyway. Non-expert here but according to the numbers below, the problem may just be that the new wheels (rim+tire) are just too much larger than the originals -- especially the front ones. The suspension could have all sorts of problems handling these differences:

FRONT WHEEL DIAMETER:
Orig: 611.4 mm
New: 647.1 mm
Difference: 35.7 mm

REAR WHEEL DIAMETER:
Orig: 631.4 mm
New: 647.4 mm
Difference: 16.2 mm
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Old 09-27-2006, 09:08 AM   #8
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I didnt read all the replys but I was told if you use wheels that require spacers you car will always ride like ass. Did you use spacers?
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Old 09-27-2006, 08:14 PM   #9
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Quote:
Originally Posted by BoxsterQc
My vibration was a real nightmare for 6 months.

My back tires was finished so I decided in the spring to get 2 Pzero. I got them installed and balanced on GForce machine. Since day number one I had a slight vibration around 75-80 mph. I went back for rebalancing and they were able to reduce the variation by repositionning the tires on rims.
Drove it for a month a nothing changed ...vibration was still there, since I thought that the tire have to be worn a bit a decided to be patient.
Decide to bring it to Porsche dealer, redid the balancing on GForce and still the vibration was there. The dealer decided to have a close look to all running mechanical pieces ( brake rotor, driveshaft etc....) nothing wrong found. I drove it another month and took it back to dealer and complained. They redid the balancing of the four wheels and they suggested to have the mags checked in a specialized place.
Had the 4 tires removed for mags and mags checked. No problem found despite the fact that I had to pay $$$$.
Went back to dealer and gave him the results of the mags inspection. At this point the vibration was a real headeach to the point that I stopped driving the car.
One evening while I was watching TV I decided to jack the car and invert the wheels position from left to side for the back and front tires.
Took it for a ride and TADAMMMMMMMMMMMM no vibration anymore, a real miracle with no explanations. I took the car to 130mph and it drives like a charm .....
Went back to the dealer seeking explanations and they gave the bull****************t lines about the fact that the car is built in a way that if you change wheels positions from original it may affect the handling and that probably the guy who installed the tires didn't respect the right positions bla, bla,bla......

Until today it's a real mystery but it's driving incredible nice and that's what it count.
i was just curious, what do you mean ''invert the wheels position from left to side for the back and front tires''?????

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