Originally Posted by datman55

SVP5TEN...the reason for the higher springrate is due to the design of the 510 swing arms, and where the spring is placed.

It's been a couple of years since I sold my 510, so the exact numbers may be a little out, but the principle is the same.......

Because the spring is placed between the wheel and the swing arm pivot point, you get a leverage effect on the spring. Because of this leverage effect, the actual springrate needs to be about (memory fading) 3 times the "wheel rate". Because the front springs do not have this leverage effect, the "wheel rate" is the same as the Spring rate.

If we were talking purely wheel rates, I would say 150-200lb on the rear would be fine for the street....that equates roughly to a 600lb spring rate (assuming 3:1)

That's the basic priniciple, I'm sure someone here could certainly correct the actual maths.

Originally Posted by datman55

The thing you have to be careful of is where your rear coil over is going to located on the swing arm. If it is in the same location as the standard spring then 800lb springs will be fine....pretty firm.....but fine. (just make sure your back teeth are in good...they may rattle themselves loose!)

If the coilover is connected closer to the wheel, the spring rate needs to be less, as the closer to wheel you go, the closer to the "wheel rate" you get. In simple terms....the closer to the wheel, the lower the spring rate.

The reason the other guys might have thought you were a little crazy was, the are probably talking wheel rates....you need to confirm this with them, as 800lb wheel rates are not crazy...they are for the clinicaly insane (ie. have all teeth removed professionally prior to them falling out from the vibrations though the car!)

BTW...I'll be in your neighbourhood tomorrow......coming over to visit you guys for a few weeks.