Standard rear springs are progressive. From memory, something line 110 - 130 - 200lbs/in. But, in the normal operating range, you'll run in the 130 section most of the time.
Tyre pessures are a little high..
What about your ARB's...?
I've just received a full set from Protech - single adjustable with spherical bearings. I re-used my front springs as I had just fitted them before the car went off the road and on testing they were considered to be fine. Anyway, the springs are relatively cheap. Had I replaced all springs the total cost all-in would have been just shy of £700. Can't wait to fit them...
Tazio that's a terrible thing to say about me
From what you are describing road use wise and car weight I would get a set of 200lb front springs. Progressive rear.
we can get that sorted - well the guys at the shop can as I am lucky enough to be in Daytona working for 2 weeks. Check out the FB feed for all the info.
we can even probably make it work with springs that could be fitted to a new set of dampers in the future thereby saving some future cost/redundancy.
we have our own progressive rear Eibach sorins made for us.
However the cheapest way would be to find some used Caterham springs and swap. The front will be as Richard said @150lb which is a little soft for my liking. Or just mix. Get some. 200lb fronts new and regular Caterham progressive rears.
Hope that helps.
Before you start throwing money around I would drop your tyre pressures and look which ARB,s you have and if they are correctly set......
Have experimented with tyre pressures extensively, this seems to give the best results, car has been set up by PGM.
ARB have been checked and have been set up carefully,
Thanks Simon, will be in touch.