philooo

The steering of my 2003 Porsche 911/996 was shaking a bit at speed above 60MPH. I went to get the four tire balanced on a proper Hunter Road force machine. But even after that, I can still feel the steering wheel shaking.

It shakes pretty much all the time. The only pattern I 'think' I observe is that when I start the car, the first miles are usually shake free. Then after a while, even at same speed, the shaking comes back.

The steering shaking is bearable, but annoying for a car that is supposed to give great steering feel.

The tires, front and back, have good thread on them. The front are 225x40x18 and rear 295x18, mounted on stock Porsche wheels (turbo II look). Stock suspensions.

The car steer to the right a bit, but I was told the alignment would not generate shaking in the steering..

Anyways tomorrow I bring the car to the shop for an alignment may be they'll find something. I wonder if some screw on the steering rack is not loose or something like that..

Anyone experienced something like that ?

himself

If you have spacers, that's the culprit. Get hubcentric and you should be fine.

-td

Sneaky Pete

Something similar happened to me last Summer. Bought new tires, had them mounted (the car was driving A-OK prior) and noticed a vibration in the right front. The place I went to had a bunch of kids using old equipment. I told them I need a 'better than good' balance. It was cheap and that's what I deserved. So I took the car down the road to a brand new Tire Barn. They had all the high tech machines. They told me (and proved) that my right front wheel had a bend in it. Not good news. They said they needed to balance the tire on the wheel by matching the wheel up with the tire. Not exactly sure what it meant but the car drove great afterwards.

So maybe you have a bent wheel?? Hope this helped.....

Macster

Have experienced nothing like this with my 996 but once in a great while with my 02 Boxster I have.

Vague sort of shimmy/vibration appears with tires up to temp while traveling down otherwise smooth roads at highway or freeway speeds.

Since I always use N-rated tires, have the tires/wheels load force balanced and keep the alignment spot on spec, I was puzzled at first but traced it the front tires being overinflated by some amount. Not much, on the order of a few psi over the cold 29 psi.

I had been experiementing with different tire pressures -- running the tires a few psi over the recommended cold psi (probably to see if I could notice an improvement in gas mileage) -- and a sudden warm up caught me and the car with tires over-inflated for the warmer weather.

Roughly tire pressure increases 1 psi for every 10 degrees (F) increase in ambient temperature. Tires properly inflated for say 45F will when a warm up has the ambient temperature rising to 65F be over inflated a few psi. If the tires already a bit over inflated...

With a quality tire pressure gage check the tire pressures with the car and tires cold. The morning after the car has sat unused all night is when I like to check tire pressures.

FYI: For best alignment result, have tires inflated properly, gas tank full, spare tire and tool kit (if car came with these) properly installed and car empty of any weight adding "junk".

FWIW: Some indy and Porsche alignmment techs like to add "ballast" to driver's seat or floor board to compensate for the driver. I have had my Boxster aligned both this way and sans any weight and could not tell the difference. My opinion is it doesn't matter. What does matter is the quality of the alignment. I like to get a before and after printout to study see what settings were off and by how much and what the new settings were.

The few times -- well at least once I remember clearly -- I failed to get this later I found out the alignment (done at a dealer too) incorrect and the sub standard alignment cost me a new pair of rear tires that wore out before their time as a result.

Sincerely,

Macster.

function12

Might see if you can get the tires road force balanced. Not all shops will have the machine to do it.

philooo

I have tried to lower the pressure, it doesn't make a difference.

The wheels where balance on a GSP9700 hunter road force, which does apply force on the wheel while balanced.

It is either the alignment or something loose in the steering, but at slow speed it is absolutely sharp, so I hope it is the alignment. I'll keep you posted.

Macster

My previous post was not intended to get you drop the air presssure below the recomended setting, only to check tire pressures were correct.

Too low a pressure will cause the tires to be more active and wiggle possibly shimmy or even mimic an out of balance condition. The tire pressure wants to be pretty close to if not at the recommended amount for that size of tire. The correct inflation pressure listed on the inside of the gas cap cover lid or in the glove box or somewhere.

What brand of tires are you running? How many miles have they accumulated? Tires vary in quality and you might have a bad set or just a bad tire, sometimes bad from new, sometimes going bad after accumulating some miles.

One possible indication a tire bad, or even a wheel bad (see below) is the amount of out of balance the tire/wheel assembly has. We never think of this until after, but if you have reason to have the tires balanced again ask tire tech to write down the amount of out of balance and advise you how these numbers compare to what the tire balance maker provides.

Also, one person was reporting a bad balance symptom and the cause traced to a noticable "flat spot" in the wheel's rim where the wheel hit something hard enough to bend it.

I don't know the history of the car and its type of usage but if you can with the car safely in the air with its wheels/tires able to spin you turn be hand each wheel/tire assembly and carefully look at the tire tread face, tire sidewalls, both outside and inside, and at the outer and inner wheel rim diameters looking for any runout either radial or axial in nature to verify each tire and wheel at least rotate with no obvious signs of out of roundness.

Sincerely,

Macster.

philooo

I am running Michelin Pilot sport with 5000 miles on them, +-50% thread left on them.

The person who balanced the tires looked at the wheels for possible damade but I admit they did not spend enough time to really be sure 100% the wheels were ok.

The best would be to have a set of wheel to make a switch, I'll see if that is possible tomorrow at the shop.

Is there anything onthe steering rack that need to be check for torque/tightening ?

phil

nick49

Tire pressure can be critical, factory recommended is fairly high and overall is best for street use I've found. A slightly bent wheel can cause this as well, as can caked mud or debris on the inside of wheel. As has been mentioned earlier, wheels center on the hub rather than by lug bolts, check this. A severly worn tie rod end could cause this, usually alignment will not unless it's been knocked way out due to an accident. Very irregular tire wear scalloping due to severe underinflation might cause this even though tires are correctly balanced. You mention the Hunter balancer, but no mention is made if the balancing was done correctly. I'd check that first!

My car has Pirellis at 30% good on front, Sumitomo HTZR ll on the rear angularly worn from 95% to 80% due to negative camber. Running 3 piece aftermarket wheels, RR was severely bent, I removed the tire and straightened in a press and had it rebalanced. Hands free over 100mph and not a hint of shake, rear feels good as well up to 135mph.

Hope you get it sorted!

philooo

what do you mean by 'wheels center on hub ? are there many ways to mount the wheel on the car ?

nick49

The hub has a raised register that locates in the center of the wheel to assure its concentricity. This is often lacking with spacers and even some aftermarket wheels that are somewhat universal rather than Porsche specific.

mglobe

It could be a bad tire.

onefastviking

Any chance there is water in the wheel/tire ?
Once you get them to spin it and zero out the balance next time ask them to spin it a 2nd time to see if it stays balanced.

htny

my bet is a bent wheel

jyoteen

Run out on the wheel is exceeded (aka bent wheel)

Rotors deformed enough, at least causing a shimmy?