Racing - Spring Rates

Can anyone please give me a good starting point for spring weights (in lbs) used for a full-race GT40?

My project isn't a GT40 but a car with similar configuration. I know the spring rate will only be a starting point and I will have to play around with rates etc once I get the car on a track. That is a long way down the line but I want to fit shocks/springs during the initial assembly to check locations/clearances etc.

Fully laden sprung weight. Shocks mounted 20 degrees from vertical:

Estimated 1149 lbs (Ford GT40 1046 lbs approx) - 41.7% (Ford GT40 45.8%; Ferrari P3 41.8%)

Estimated 1609 lbs (Ford GT40 1240 lbs approx)- 58.3% (Ford GT40 54.2%; Ferrari P3 58.2%)

Any thoughts on suitable spring rates in lbs as a rough starting point? What are racers currently using on the GT40?

The aim is to race the car against the cars it was designed to compete against in period - GT40 and Ferrari P3. The project is detailed here Jaguar XJ13 | Building the Legend
If I were guessing- which I am- I would guess that 650-700 in the front would be a good start, with 800-850 in the rear. These would be for racing, not for the street.

Depending on the final rear weight, I could see the spring weight going up more there.

Ian Anderson

Lifetime Supporter
It all depends on where the spring attaches to your wishbones / uprights.

say for arguements sake you only manage to attach the spring half way along the wishbone then you will need double thespring rate than if you attached it right at the end.

But attaching it right at the end will not be an option either (There will be a wheel there!) so you will need to give some dimensions before anything more accurate can be confirmed

It all depends on where the spring attaches to your wishbones / uprights.
Good point Ian!

The spring (actually the damper lower centre) attaches 3" from the outside pivot point of a 11.5" lower wishbone.

Front and rear setups are very similar in this dimension.

Here is a scan of an original 1966/67 document that I completely fail to understand in case it helps ... :stunned: