Yeah I know mate but the rta laws have changed now there is no capacity limit as long as brakes, suspension etc is all up to the engine specs

awsome, they wont pass that now , dont let it run out of rego,

Yeah that's A fair point I'm going to wack in 200 and see how it likes
it then ill go from there wards.yes it's registered with the 13b turbo

hi datrotor , we use 150 or 175 on rx7 racecars so looks like your close but you will have to try a few different rates and see what it likes . the position of the instantanious center of the rear 4 link arms and in turn the antisquat/squat ratio will need to be concidered as well , is this car registered with a 13b turbo?

Yeah he was Thinking around the 200 mark.going get 200 and see how they go.then ill know exactly.lucky there not to expensive

Yeah I'd say around the 175 give or take, the best way is to measure the weight of the car front and rear and your mate should be able to sort that the he should know the calculation to find the right rate spring, there is a lot of info on Ozdat about this!
You can google the conversion for weight to spring rate as well!

yes, that will need higher spring rates to get the same effective rate at the wheel. you'll need to work out, or measure, the motion ratios as well.

Thanks for that L18 my shock mount are in further then standed leafs as I have 17x10 wheels in the rear.the shocks work out about 650mm centre to centre of each shock.standed leafs would be more like 900mm centre to centre.so they are in a bit more.would this mean a little more then you just predicted?

250lb is 4.5kg. Too stiff imo. But it depends alot on what the wheel rate works out to be, which depends on how far inboard your lower coilover mount is. Assuming its in the standard location for the shock, I say that's far too stiff for a street car.

I don't know where dattodude got that figure from, but it's either a typo or a plain old mistake. Kings lowered leaf springs for 1200 are 150lb/in.

What's soft for a race car on slicks or semis can be hard for a street car on normal tyres. The more grip you have the stiffer the spring rates you need.

Unless you have 50:50 weight distribution, I wouldn't be going for the same spring rates front and rear if the rear is anything like 1:1 motion ratio - it will make it very tail happy!

This page from Pitroad shows the spring rates they use on the heavier B310 4 link rear end. http://translate.google.com.au/translate?sl=auto&tl=en&prev=_t&hl=en&ie=UTF-8&eotf=1&u=http://www.pitroad-ts.com/A-parts-2/bushing/spring-rr310.htm&act=url
The Pitroad spring 3kg is what they use in their TS Cup race car on 9" wide rear slicks. That's 165lb/in. They cut 2 coils out of it for the race car which will make it slightly higher rate - say about 175lb/in at a rough guess.
The normal spring 1.7kg is the stock spring rate, which is 95lb.
NISMO 2.26kg is 125lb.

The best bet for a custom setup is to go to a race type suspension specialist, get the car scaled and work out the natural frequency as a starting point. Anything else is just taking a shot in the dark. But if that's the approach you want to take, I'd start around 150-175lb assuming the spring location is pretty much where the leaf spring was.

Anyone got anymore suggestions? I have 250 pound fronts.rears are vertical.im thinking 250 pound rear too.will this be to soft you think?