Settings for a street driven GT40....

[Cliff Beer]

I'm putting my cav GT40 back together now after replacing the front and rear uprights with much stronger (and better designed) fabricated pieces, refinishing the A-arms (powder coat - looks great), and various other improvements and detail tasks. Will post some pics shortly.

I marked and measured all the suspension settings before the car came apart...caster, camber, toe, ride height, etc. However, with new suspension pieces installed the car is going to need a full re-measure and re-set to what's optimal. Optimal for a street driven '40 that might get the occasional amateur track day once in a while, that is.

So what are most people running for a '40 used in this manner? The car runs 60 series rubber on the front and 50 series rubber on the rear. Primarily, the settings should be optimized for comfortable street driving. If I'm a little slow on the track because I don't have enough negative camber, well, that's just fine.

Recommendations for both front and rear for camber and toe, and caster for the front?

Thanks in advance.

ps. a few random/somewhat related pics attached 'cause every post should have a pic....

 

[David]

Sorry I don't have any recommendations but nice uprights, alloy or steel? I'm guessing steel, how much do they weigh?

 

[Cliff Beer]

Hi David,

Thanks. Yes, they're very nice. Steel. Made by Ian of CAV Canada. Very, very strong, but not particularly light. The idea behind these uprights is to set the suspension up with the right geometry, and have uprights that will take a beating through all kinds of punishment. Lightness (unsprung weight) was third or fourth on the list. Unfortunately, I did not measure the weight of the new uprights. Ian might see this thread and be able to post some weights for us.

 

Hi Cliff, I have CAV GT40 51 and have experimented with various set-ups over the years. I am running 15" wheels with 225/60/15 tyres at the front and 275/55/15 at the rear. I have the standard spax shocks but have stiffer springs 425lb at the front and 550lbs at the rear.
For the street I found the following set-up to be good:

Ride height - 4.75" front 5.25" rear
castor- 3.5 to 4 degree (any more made steering too heavy)
If you have Ians new rear A arms then there is already some built in rear castor.

toe- front and rear slight toe-in maybe 1mm total
camber- front and rear 0.5 degree negative

shock rebound stiffness 14 clicks

I hope this helps
camber-

 

[Cliff Beer]

Hi Cliff, I have CAV GT40 51 and have experimented with various set-ups over the years. I am running 15" wheels with 225/60/15 tyres at the front and 275/55/15 at the rear. I have the standard spax shocks but have stiffer springs 425lb at the front and 550lbs at the rear.
For the street I found the following set-up to be good:

Ride height - 4.75" front 5.25" rear
castor- 3.5 to 4 degree (any more made steering too heavy)
If you have Ians new rear A arms then there is already some built in rear castor.

toe- front and rear slight toe-in maybe 1mm total
camber- front and rear 0.5 degree negative

shock rebound stiffness 14 clicks

I hope this helps
camber-

Thank you, very helpful. That's kind of what I was thinking too as a baseline setting. Not too extreme in any regard. My ride height in front is a bit lower...not by choice unfortunately, I think my springs are sagging pretty heavily (need to replace).

A pic of the front suspension back together....

 

Hi cliff, please let me know how the car feels with the new uprights. Ian clarkes new A-arms at the rear in my car made a noticeable to the handling, it made the rear more predictable and more planted. I have also replaced the front rubber wishbone bushes with Nylon ones and also installed polyurethane steering rack mounting bushes. These changes made the front more stable under braking and turn in is sharper and there is a greater feel to the steering wheel.

 

[Jimmy P]

Sibbat, Cliff, At what place at the front and rear of the car are you measuring the ride height? Also do you see any benefit from corner weighting the car? Lastly, what can I expect if I run a ride height of say 4.25 - to 4.5" at the front and just .5 " higher at the back? What I mean is will the handling be sharper one way or the other with increased steering input rquired etc. Will look forward to your response which is much appreciated.

 

[Cliff Beer]

Sibbat, Cliff, At what place at the front and rear of the car are you measuring the ride height? Also do you see any benefit from corner weighting the car? Lastly, what can I expect if I run a ride height of say 4.25 - to 4.5" at the front and just .5 " higher at the back? What I mean is will the handling be sharper one way or the other with increased steering input rquired etc. Will look forward to your response which is much appreciated.

Hi Jimmy,

Getting right to your points....

1. I'm measuring the front at the lowest point, which on my car happens to be right at the forward A-arm mount.

2. Not sure if the ride height of .5" higher at the back will sharpen the handling. It will, however, help ensure you're not packing a high pressure zone under the floor pan at high speed. In other words, while our gt40 replicas don't have downforce tunnels and venturis and such, we can at least ensure we don't have an upward plane of the relatively flat floor. At speeds over 100+ this can make a difference in how planted the front end feels (and actually is!).

3. And, yes, corner weighting is advisable. There's a basic process to it that involves replicating wet weights with driver, detaching the sway bars, setting the ride height and then measuring from there. There's definitely some finesse to doing it right.


Cheers.

 

[Jimmy P]

Cliff, Much appreciated. I'll put your words into practice for sure!!

 

[Steve26]

Hi Cliff,
I set my car up today to 4.5" in front and 5.0" in back with 1deg. neg. camber all around and .050" toe all around. It has been three years since I've checked/set the suspension and it was way off. My car was light in front and the steering was too quick at 100+ but it is much better now! The biggest problem was the rear spring preload was way off (spring sag) so the front and rear ride height was the same at 4.5". I had it up to 110MPH this afternoon and it was very stable, hope to get it up higher later if the opportunity presents itself. We should get the Washington crew together before the weather changes and go on a run.