MikeO

I'm taking my recently acquired '98 C2S to have the wheels balanced and the car aligned on Monday due to a shimmy in the steering above 45 mph and the premature wear of the tires.

A couple of questions:

1) Where can I find the alignment specs so I can double check to make sure it's being done to factory specs, or is there a "better" alignment for the C2S's to have?

2) If for some reason balancing the tires does not cure the shimmy (vibration), I'm guessing the front tires may be bad, in which case I'll replace all 4. Any particular brand (besides the P Zeros now on the car) that I should get?

Don Magee

The factory alignment specs will give you good tire wear, but will also insure significant understeer.I have minimal toe in(can't recall the exact amount) and 1.5 degrees negative camber front and rear. This is my agreesive street alignment.Bruce Anderson's book has slightly diffferent specs-- toe out as I recall.On my setup, tire wear is even, but I corner it hard. Rubber choice is a hot, and personal, topic;Bridgestone Re730 work fine on the street, wear well, and are cheap.

Chris in Detroit

Mike

(1) Check wheel torque with torque wrench - should be 94lbft. Incorrect torque caused wheel shimmy for me.

(2) Have wheels balanced - this might correct shimmy

I would check (1) and (2) before going any further

(3) Alignment specs for USA Carrera S:

Note: ' is abbreviation for minute, 1/60 of a degree

FRONT
Toe, unpressed (total) +5' +/-5'
Toe difference angle -40' +/- 30'
Camber -20' +/- 10', with max left to right difference of 10'
Caster 5deg20' +15'-30' note to try and achieve this exactly

REAR
Toe, per wheel +10 +/-5' with max left to right difference of 10'
Camber -1deg10' +/-15' with max left to right difference of 20'
Kinematic Toe-in Change 1.5 scale units

Note, it is very likely that only Porsche dealer will have the Porsche scales for the kinematic toe - and may not usually perform the check unless you ask

(4) Tire Wear - since recently acquired, I'm not sure whether you mean uneven tire wear ? Anyway, enthusiastic driving can wear through rears in 4000 miles, although most people seem to get 6000 miles + out of them.

(5) Tire Brand - see other recent threads. Pirelli, Bridgestone, BFG - all have their supporters and critics.

(6) More aggresive alignment - try increasing front negative camber to -45' to --1deg. For reference Carrera RS had -1degree. Will result in better turn-in and front grip, dialing out factory understeer, but note car will feel more "twitchy" in straight line - and front tires may wear on inside edges.

MikeO

Chris,

Thanks for the alignment specs.

I've already torqued the wheels to 94 lbs., and it made a slight improvement, but the car still shimmys from 45 mph.

Re tire wear, the tires have 3000 miles on them, and the rears are somewhat worn out from the centers to the outside edges.

Jim 97 C4S

Mike,

When I purchased my 97C4S it had a slight shimmy. Turns out that I had one Turbo hollow front wheel. The other front and two rear wheels were the standard C4S non-hollow type. If this is your problem it can be corrected by matching the wheels.

Jim

MikeO

What I'm really concerned about is that I may have a slightly bent rim or perhaps that one or both of the front tires has a cord broken from hitting a curb or pothole. I sure hope it's not worse, and that I have a messed up front suspension.

I paid top $$$ for the car, and had the dealership I bought the car from put it in writing on the Bill of Sale that the car was perfect both cosmetically and mechanically, so if it turns out I have a bent rim, damaged tire, or a messed up front suspension, I'm going to have to try to make them pay for the fix, which they should. If it's just an alignment issue or the wheels just need balanced, I'll live with that.

Terry Adams

If the vibration is constant at all speeds above 45, sounds like a bent rim. The 18" Technology, if that is what you have, are quite vulnerable to road imperfections and curbs. See a rim repair shop like http://wheeltechniques.com/index.html in your area. If the vibration is at 45, and goes away till it comes back at a higher speed like 90, you need to get all 4 balanced on a Hunter 9700.

MikeO

The vibration is constant above 45 mph, so perhaps I may have a bent rim as you suggest.

I'm going into my Tire dealer I've worked with for nearly 20 years at 9:00 this morning to let him try to spin balance the wheels, and to see if I have a bent rim or bad tire.