I was just Wandering...

Leland Pate · 08-20-2002, 05:18 PM

Ok, what have I done to my car...

Lately, my car feels extremely unstable at high speeds.
If I'm doing over 65 or so, and make even the slightest movemment either right or left... the car does that strange "wobbles back and forth for a few seconds" thing. And if there is a strong crosswing (common here in southern Idaho) you can foget it... the car pitches side to side with the strong gusts.
I've never had this problem before.

The only thing i can think of that it could be related to is either the new tires (air pressure?) or maybe something to do with the amount that I lowered the car???

Has this ever happened to anyone?
Anyone want to point me in a direction?
A 911 should not be so twitchy...

TimT · 08-20-2002, 05:25 PM

sounds like you have some alignment issues.....911's become increadibly sensitive to the "rutting" or wheel paths in the road when they are lowered or the alaignment is changed from the factory specs...

The factory aligned the cars to push, and to be driveable and correctable. Increasing camber, lowering the car and installing performance tire will make your job as a the driver a little more "busy"

Bill Douglas · 08-20-2002, 05:31 PM

Leland. I think it's those f'ing 17" cup type wheels. Why don't you pack 'em up, put them in a box, and send them off to the colonies (Wellington specifically) as a punishment.

Early_S_Man · 08-20-2002, 06:39 PM

Lee,

If you are certain the problem wasn't there before your flat tire adventure ... it may be the new tires! Try swapping the left and right front wheels, and see if the problem changes in any way ...

There have been similar problems reported in Road & Track that were cured by either swapping the left & right, or by changing tire brand and style! In some cases the tires are defective, and swapping sets of tires for a new set of the same varietyy cured the problem.

Chris Bunker · 08-21-2002, 08:11 AM

I've noticed the same thing with my 78 since I mounted up the 225s on the 8X16s up front. Not only are they more sensitive to truck ruts (tramlining) but it does also seem a bit twitchy at higher speeds. I noticed it the most during my recent return from vacation (750 miles in a day). I had put a lot of miles on during the whole trip, almost 1600 or so. I checked things out once I got home and noticed the front wheel bearings where a bit on the loose side, so you may want to have a look at those Leland.

Chris Bunker
78 SC

pwd72s · 08-21-2002, 09:17 AM

Lee, to me, alignment has always been a bit of voodoo science. But Warren's post would be a good, and free place to start. After that? I hope there is somebody near you who is good at Porsche alignment...because it's not like aligning your Dakota!

Leland Pate · 08-21-2002, 09:37 AM

I haven't been in the Base Hobby shop since April (I have a garage now), but yesterday i went in to retrieve my engine stand and low and behold.... they've got a full up alignment rig in there!

It's so new, I'm not sure if anyone even knows how to use it properly, but it certainly looks nice... I think it's the same thing they have at Les Schwab... It also appears to double as a drive on lift.

Maybe, I can convince someone to sit down with me, my car and my manuals to see what is going on with my suspension.

Thanks for the tips though guys...

Superman · 08-21-2002, 12:53 PM

Leland, I'd consider that a HUGE bonus. If I thought the armed forces would take me, I'd enlist just to use the alignment machine (kidding of course, but staying out of the military was probably one of my big mistakes....I don't even make my bed in the mornings). Anyway, I'd play with alignment until I LOVED the way the car handled.

You should check alignment first. Alignment geometry has a POWERFUL influence on how the car handles and could easily be the cause of your wandering (at least your automobile's wandering that is). I'm thinking your tires could also be contributing.

stuartj · 08-21-2002, 03:55 PM

Hey Leland

I reckon alignment is the place to start, especially given your other post re understeer at an event. But its a black art- spring for a 4 wheel alignment at a P shop that does competitive cars.

I would bet that solves the problem-and if doesnt, (assuming your suspension is in good order, etct etc, then your probably right about those Falkens.

stuart

pwd72s · 08-21-2002, 04:11 PM

Lee, reading the spec book on my car, Porsche wants a bit of toe in at the front wheels...I think it's zero degrees, "pressed", if memory serves. That means with a bar of a certain poundage pressure forcing the wheels outward. In other words, if both wheels are toes OUT when you're driving down the highway, you will get wandering, lots of it...but if the toe is straight, or even a tiny bit in when moving, you will track straight. The thing is, front wheels will tend to toe out as you gain in speed. So, when at static rest, you want a smidgeon of toe IN. Like maybe 1.5 or 2 degrees unpressed? Like I said a voodoo science....but if you have one of those little white covered "technical specification" books as published by Porsche? The specs for your SC should be in there.
I'm thinking maybe your front is running a bit of "toe out", thus the wandering. Sure hope somebody who knows more about this than I will add something...

Superman · 08-21-2002, 07:13 PM

Agreed. A little bit too much toe out will cause the car to be a little darty, particularly at higher speeds. Dartiness at high speeds is a bad thing. I'd also agree that the Porsche performance experts know best how to set up Porsches. A good friend and excellent autocrosser had a 4-wheel alignment done on his AX 914 recently. This car (and driver) has won the local (and highly competitive) GTU class the last two years running at least. He gained 1.5 seconds! For those of you who do not autocross, 1.5 seconds is HUGE. That margin can separate first from tenth place.