Before anyone chimes in about Force Balancing read the entire post.

I have a 2003 Boxster S that has a high speed vibration in the front that starts around 75 and clears somewhat as you pass through 90. It's definitely speed sensitive and increases in rate (not intensity) with speed. It is not rpm related as it occurs regardless of the gear I'm in.

I have tried 3 sets of wheels (2 18" sets and one 17" set) and 5 sets of tires over the course of the last year and while the problem changes (intensity changes due to sidewall stiffness, etc) the problem persists. All of the wheel / tire combinations have been force balanced on multiple machines using the .10 oz settings. The current wheels are BBS forged and measure true to .001"

Since the only thing left that's rotating is the hub and rotor I'm thinking it's either a front wheel bearing or a warped rotor. Since I get no pulsing with the brakes I'm leaning toward the wheel bearings. They pass all static tests but that doesn't mean on of the bearings isn't damaged.

Any thoughts, suggestions?

 

hows your alignment

 

I think if it were a wheel bearing you would here it at a much lower speed and be very pronounced!!

I lost a front wheel bearing and like you, started looking everywhere except the bearing.

 

if its bad enough to vibrate there should be some noise from it

 

I've had warped rotors and the only time you notice them is when you use the brakes, so I doubt that is it. Could be a wheel bearing, but with all those wheels going on and off, I am sure you "checked" them for tightness, right?(!). Alignment is next. How many miles on the car? Is it possible something is bent?

 

First, i dont believe RFB is a panacea. It conteracts out of round, but does nto correct it. Given the number of bent wheels I've seen, i see RFB as a crutch that obscures the real problem. I'd do a visial inspection of wheel/tires as the spin first.

Next I'd look at suspension bushings. They can allow play that makes any imbalance a problem.

Grant

 

13,000 miles
alignment set 200 miles ago
Wheels checked for round and measure <.01" radial and lateral
RoW M030 suspension installed 1000 miles ago, vibration unaffected

Hey, it might be a tire since the vibration is different between the track 17's and the street 18's but the force balance was less than 10 lbs when they were installed. It will go to the dealer soon to get looked at again.

Next!

 

I don't think a slightly warped rotor would lead to an out of balance condition. There would not be a weight transfer to a different point around the circumference of the rotor due to warpage, there would just be a variation or "wave" of the surface or "plane" of the braking area in relation to the plane of the brake pad.

I have had high speed vibrations and they were cured by new tires every time.

You mentioned that it will go to the dealer to get looked at "again"....You may wish to take it elsewhere.

 

75 mph? Is your spoiler extending?

 

99% sure that it is but it's one more thing to check. Not exactly sure how the spoiler being down would cause vibration in the steering wheel but hey, you never know.

Thanks

 

ID BE CURIOUS TO SEE THE ROAD FORCE PRINT OUT AND THE ALIGNEMT SEPCS

 

Road force was 8 lbs right front, 6 lbs left front. Balance set to .10 oz accuracy 0.0 on all 4. Typically you shouldn't feel anything under 10 lbs road force. Since the wheels measure almost perfectly round indexing the tires had virtually no effect.

Front alignment is set to RoW M030 specs with some minor tweaks.

Front Camber -.06 -.06
Front Caster +7.9 +7.9
Front Toe +5' (~1/16th toe in)
Rear Camber -1.8 -1.8
Rear Toe +5' (~1/16th toe in)

The rear camber setting is a tad more negative than I initially wanted due to the geometry not allowing for toe in with less camber. We set the toe first then brought the camber up as much as we could. The next time around I'll dial in a full -1.0 on the fronts as it heated the fronts a bit too much at the last autocross. I'm gonna play with the toe settings a bit too but turn in is pretty good and I don't want to give up high speed stability for what little I autocross the car.

Tire wear is irrelevant to me. This is my toy and if you want to play you gotta pay

Hey, for all I know the tires have taken a set and need to be re-indexed. I'll find out when I get off my lazy butt and take the car into the dealer.

 

id like to see the actual printo out for the aligmnet

 

This may be a silly question, but are all of the wheel bolts the same or do you have a locking bolt in one location?

High frequency would seem to indicate something wrong in the hub, most likely a bearing that is bad (not to the squeeling extent) or improperly preloaded. It could also be something aerodynamic. Have you checked out the undertray stuff?

Bro

 

Sorry, but I'm not inclined to go out to the car, scan in the document and post it when I helped the mechanic dial the car in........ Trust me, those are the numbers (with me in the car BTW)

One thing to note, initially the front toe was way out, almost 1/4" toe out and the vibration problem was severe. Dialing it back to spec reduced the intensity but not the frequency. That's what leads me to believe it's something as simple as a loose or dry front wheel bearing or perhaps a suspension bushing. It wouldn't be the first time I've seen either of those problems on a 3 year old car, regardless of mileage.