total rotating mass (hub, rotor, 5mm spacer, and wheel only) has an axial (side to side) run-out, measured with a dial indicator of .028in (28 thousandths). Measured on the outer edge of the 18" wheel next to tire bead. Is this within spec.? Alignment and RF balance done. steering wheel vibration at ~68 mph and again at ~120 mph.

 

are you saying the tires and wheels are perfect on the rf balancer

 

My 996 Turbo reference gives a 0.7 mm number for both lateral and radial runout for "light alloy wheels". Assuming this is the same for the 996 NA "light alloy wheels" that's 0.0275" which puts your wheels out of "spec" by 0.0005".

Even if you were measuring "just" 0.0275" I'd have to offer an opinion that 0.0275" (or 0.7mm) is pretty lousy and it is not surprising that the steering wheel vibrates.

Are you sure there are no burrs on the spacer? They can get banged together and a burr can be raised.

Be sure both spacer surfaces are smooth, the burr can be on the face and not on the edge, and parallel and the hub face is likewise smooth and free of any burrs or grit or something. Run your hand over the hub face, and the spacer faces, and the wheel were it presses up agains the spacer.

Check the spacer centers properly on the hub and the wheel too without and with the spacer in place.

 

Wish I had known to ask for report, just know they said they balanced fine.

 

Thanks Mac. I've checked the surfaces and aligned the spacer. Need to pull the spacer and check at the rotor, then finally check at hub surface.

 

so with the balancing, they just balanced the tires, they didnt do any of the rf balancing indexing or check wheels or anything else. Thats normal unless you complain of a problem. Now you have a balance problem and you can have them analize all the wheels again and see if they are perfect or not.
you can check anything else on the car you want to, but when you get back to the wheels, this is what the road force balancers are for

 

Have you tried switching wheels from side to side? If the run out moves with the wheel, you know it is a problem with the wheel, and not the spacer, hub, etc.

 

RF balance was done properly, just didn't ask for a report.
Run-out is the same for both wheels, both sides of the vehicle. ~.028+/-.0005
Macster, what do you think I should see. less than .018 at the rim, assuming .002 max for hub and rotor assembly.

 

how are you measuring the runout?

 

see original post.

.018 at the rim is a calculation derived from Porsche posted max run-out of .002 for hub and rotor, projected to an 18" wheel.

I will be checking actual values today.

Mac at what point on the rotors and hubs should I position the dial indicator?

Really just needed Porsche's max run out at the alloy wheel which Mac provided to determine if rotating mass exclusive of tire was in spec.

vibration may be just the tire

 

what I meant, is what is the method you are using?
how are you physically doing the measurement?

 

Your question drove me to look at my factory manual reference and this is what it has to say:

Maximum permissible radial runout and lateral runout of the light alloy wheels = 0.7 mm. Maximum permissible radial runout and lateral runout of the wheel with tyre = 1.25 mm. Values less than 1.0 mm better around 0.5 mm are desirable.

Based on the above and assuming the same applies to the NA car's wheels you would want to see not 0.7mm or 0.0275" but instead 0.5mm or 0.0195" of runout at the wheel periphery.

I've never checked the run out of either my Turbo's wheels or Boxster wheels so I do not know what they have but I have observed at various times various wheels of both cars spun by hand -- while on the lift and being checked for tire or wheel or rotor condition -- and as an ex-machinist I can spot run out a mile away and the wheels appeared to have negligible runout which based on my experience puts the run out down in the 0.005" range.

Do all wheels manifest the same runout? If not then I would think you should at least have the run out the same as the wheel or wheels that have the least amount of run out.

Is the run out symmetrical in that is the high spot matched by a low spot 180 degrees away? Or does the runout suggest the wheel has a potato chip shape? If the latter the wheel or wheels could be bent.

With the dial indicator against the wheel can you see any signs of play if you grasp the wheel/tire and give it a wiggle like you were checking for bearing play?

There should be some and you'll have to check all 4 wheels to find what the lowest amount is this being then what a "healthy" bearing would have, assuming at least one wheel bearing was good.

Might mention the few times I've checked for play I have found very little play. I can't put an amount to the play but the amount of play was slight.

 

Generally run out is checked for as far away from the center of rotation as possible, and of course you would like a machined surface.

But unless you feel pulsing when braking I really doubt the rotors are running out.

Most often if an otherwise good wheel -- good as in not bent -- is running out the problem lies at where it mounts to the hub or where the hub mounts to spindle.

As the rotor is part of the hub and the braking is pulse free this suggests the wheel -- or the spacer -- is the culprit.

And as you observe, the problem may lie with the tire, or tires.

There have been a few cases where a tire balances good, even road force balances good, only to manifest balance symptoms when in use. The problem was traced to a bad tire, with bad belts, that under load and the stress of supporting the car during actual driving, that shift and the tire's balance and possibly even roundness changes.

 

Thanks Mac, been chasing the same issue for a few years over three sets of wheel and tires.
RoW 030 sport with ~GT3 alignment. You ever delve into suspension harmonics? vibration noticeable at ~68, subsides then gets my full attention at ~118-120

 

Hard to imagine 3 sets of wheels and tires all having a problem. Just thinking out loud but I assume all wheels were name brand wheels and ditto the tires?

What has been the common denominator through your trials and tribulations?

Suspension? Alignment? Wheel bearings? Spacers?

I've never really had to deal with suspension issues other than relatively minor ones brought about by well, relatively minor mis-alignment issues.

Some years ago when playing with tire inflation pressures over-inflation of not too many PSI -- just a few in fact -- I found can cause vibration in my Boxster that is indistinguishable from vibration that arises from tire imbalance. Never bothered to experiment with my Turbo. I set its tire pressures to just a few PSI under those given on the inside of the fuel door -- these are for a fully loaded car -- and the car steers, handles, and rides just fine and tire life is very good.

Also, over the years even though new tires start out vibration free that as they wear vibration comes back but a rebalance cures this. The word I get is this behavior first appeared with Cayenne tires -- their size was blamed for their susceptibility to this -- but this vibration arising from tread wear has migrated down to the smaller tires so even my Boxster's 17" front tires can sometimes use a rebalance about half worn down.

Regarding RoW 30 suspension: When I looked into having my Boxster's suspension refreshed and talked to the techs about this and brought up the idea of installing RoW into my Boxster my tech buddies talked me out of it. Both said while the RoW was an excellent suspension for track use they also said it was a bit stiff for street use.

(Might add they talked me out of any suspension freshening as the car in spite of the miles still drove just fine -- both road tested the car at different times -- and said for now to leave well enough alone unless a shock developed a leak or some other suspension component developed sufficient wear or suffered an outright failure.)

Now I hate to blame the RoW in your car's case, and I'm not going to, but I have to ask is it possible that just perhaps you are just mistaking the harsher ride and etc. produced by the RoW as something amiss with the tires/wheels?

As an aside: I have not ridden in any Porsches with track suspension but I've ridden in other cars with track suspension, Corvettes and Camaros and such, and on the street the ride is atrocious. But I daresay bad enough tire imbalance would have to be pretty bad to be felt. Now on the track I'm sure the owners would note tire imbalance right away.

Regarding alignment, have you tried a less aggressive alignment just to see if this affects the symptom?

Without knowing the history of the car, are the alignment adjustments reasonable or does the tech find he has to adjust some settings all the way to the stop, so to speak, in order to bring the car into alignment?

I bring this up as it is possible the car is "bent" and alignment is being used to "straighten" the car.

Were I faced with what you are faced with -- and I hope I never am as these can be a real pain to trouble shoot -- I would start out at the bottom and ensure wheel bearings were good, the spindle hub run outs in spec, along with the rotors, spacers and then the wheels and the tires.

You have to check and double check every step of the way to be sure you miss nothing. If there is a problem in this area, it might only be one bearing, spindle, hub or rotor. If you get sloppy and miss this...

I could toss in that you must be sure all the suspension components are in good shape, with nothing bent, or broken, or worn out. You have to be sure everything is installed correctly and even that the right parts are installed.

One other point and that is the axle half shafts. I was taught when removing a drive shaft or half shafts to always mark the assembly *before* disassembling so upon reassembly the driveshaft would be bolted up with the same relationship it had with the tranny and diff flanges. The same goes for the half shafts. A slightly out of position half shaft could manifest something maybe indistinguishable from tire imbalance.

Long winded I know. Wish I could just say the problem is 'A' and be done with it -- though of course not before modestly accepting the accolades -- but I can't.

Unless you have an 'aha' moment you are faced with a slog to sort this out, get to the bottom of it.