New Superformance darting L or R at only 40mph.

[Jim Kreber]

I'm looking for help and trying to find the cause of my car being very scary to drive even 40mph. It suddenly darts left or right over any road undulations. I bought this car with 300 miles on it and am afraid to take it out of my neighborhood. I have inspected all of the suspension components, re-aligned front and rear. I've removed the front springs and checked for any bump steer which was very minimal. I'm sure Superformance had any bump steer dialed out since their beginning. I'm trying to find out what I'm missing.
The car is the widebody with Avon 12.5/25-15 rears and 9.1/23.5-15 fronts.
Any ideas would be appreciated, thanks.

 

[Blas]

I assume you have looked at your tire pressures. What pressure are the tires at? A tire with a defect can cause the car to dart back and forth (a cone shape defect or defective cord) I'll assume you have gone thru the suspension components already. Nothing loose, etc. No excessive play in steering box. This is a new build or just new to you?
Blas

 

[Blas]

Has the car been corner balanced?

 

[Rob Klein]

Were the tires balanced the wheel weights if they are not tapped down will leave the wheel pretty easily

 

[Blas]

I assume the steering is smooth and shows no tendancy to bind also.
Blas

 

[Rob Klein]

Gaffer tape over the weights keeps them on

 

[Devin]

Almost guarantee it’s something off with your alignment. I would get the dealers recommended specs and take it to a good alignment tech/shop and see what needs to be be realigned. Highly recommend a shop with a Hunter alignment system,

Devin

 

[Blas]

Send me the alignment specs you used and I'll compare them to what's in my owners manual. Include ride height. Did you do the setup after the drivetrain was installed?
Blas

 

[Neil]

I'm looking for help and trying to find the cause of my car being very scary to drive even 40mph. It suddenly darts left or right over any road undulations. I bought this car with 300 miles on it and am afraid to take it out of my neighborhood. I have inspected all of the suspension components, re-aligned front and rear. I've removed the front springs and checked for any bump steer which was very minimal. I'm sure Superformance had any bump steer dialed out since their beginning. I'm trying to find out what I'm missing.
The car is the widebody with Avon 12.5/25-15 rears and 9.1/23.5-15 fronts.
Any ideas would be appreciated, thanks.

Check for bump steer, primarily toe-out.

 

[Ole Nylende]

The manual says 15 minutes toe, not sure if it is negative or positive.
I would do an alignment and adjust the toe as close to 0 as possible or a little tad toe in, toe out can make a car act the way you describe.

 

[David Garton]

Caster will cause the symptoms you have . That is changed with ride height thus changing spindle angles . Does the steering wheel return on it's own when you turn and let go of the wheel?

 

[Ian Anderson]

Tyre pressures
I found 20 to 22 psi front
And 24 to 27 rear

Are the wheels fully seated on the splines and centre nut torqued correctly

Also make sure everything is tight in the rear and it is not rear steering you

 

[Malcolm]

Suspension aligment is my gut reaction to those symptoms. Also don't forget to check your rear wheel toe as that can have weird effects if not set correctly. Often overlooked.

 

[Rob Klein]

and while you are at it " Wrap a hot towel around your head"

 

[Mark Coulter]

I'm looking for help and trying to find the cause of my car being very scary to drive even 40mph. It suddenly darts left or right over any road undulations. I bought this car with 300 miles on it and am afraid to take it out of my neighborhood. I have inspected all of the suspension components, re-aligned front and rear. I've removed the front springs and checked for any bump steer which was very minimal. I'm sure Superformance had any bump steer dialed out since their beginning. I'm trying to find out what I'm missing.
The car is the widebody with Avon 12.5/25-15 rears and 9.1/23.5-15 fronts.
Any ideas would be appreciated, thanks.

I would agree with Devin--check the alignment. If they can adjust in more caster i would do it. I increased my Cobra caster from 3 degrees to 5 and it made a big difference with what i call bumpsteer. I eventually got rid of all the bumpsteer by installed electric Power steering and increased caster to 7degrees--go right down the hwy no problem--let go of steering--no problem

 

[Ed White]

Tyre pressures and tracking almost definitely. Have it 4 wheel aligned by someone who understands what they are working on. Probably not kwik fit or the like

 

[Lee Patterson]

When you say Avons - are they grooved race tires? Bias ply? I have a set on a wide body Pantera and they felt like I was driving on soft rubber bands. They were not suitable for street use (which of course I already knew but tried them anyhow). It was a quick experience. They were all over the road.

 

[Jim Kreber]

Thanks for all the responses. My tire pressures are 25psi fronts and 27 psi rears. When I realigned the car we set it as:
Front toe 0.18" in
Camber 0.6 degree neg
The caster is not adjustable.

Rear toe 0.12" in
Camber 0.1deg neg (this was 0.1 pos on right side and 0.3 neg on left side)
After the realignment I could tell no difference in the handling.
I haven't been able to measure caster on the rear but it seems roughly 6 - 8 degrees pos. I'll try to set up a way to measure it exactly so I can make sure both sides are equal.

As far as bump steer, I have 1/4" toe at full compression, and 0" at full lift with the springs removed - which seemed pretty good to me.
I was also wondering about corner weights. Right now I don't have a set of scales to measure them. I'm only going by the compressed spring length (which I know can still be off).

 

[Rob Klein]

My SPF was a 69 spec extra wide body, and what Lee said is correct. If you are driving with grooved slicks, you have to pay attention to the crown in the road. Where the pavement meets is always a little dicey, and you have to hold onto the wheel. I loved the avon's so I just learned to deal with the fact when you changed lanes you were going to get help from the tires.

 

[Jim Kreber]

Rob, yes. mine is also an extra wide '69 spec car with the grooved wide racing Avon's. I also know there is a lot of scrub radius on the fronts, but I have another car with at least that much and it doesn't feel that bad.
Also, my ride height is 4-3/4" front and 5" at the rear. The steering is very smooth, and all components are tight as they should be front and rear.
I am comparing everything to my RCR P4 which also has grooved Avon tires, although not as wide and are radials. I had some bump steer in that car originally because I moved the suspension pickup points, but I eventually got it dialed out. I would just love to get the GT40 feeling a little more stable.