New springs and ride height

[clarkey]

I have a 1998 wide track car with adjustable platforms. The previous (front) springs were the standard ones, and had a free length of about 7.5". I bought some 300lb springs from Caterham (possibly a bit stiff, but I'll give them a go), and these have a free length of almost 9".

 

Caterham say this is correct (no other length is available), but I can't get the ride height correct, it is FAR too high. I've searched on various posts about moving the circlip up the damper. Is this what I need to do? It looks like there is only one groove on the damper body - the other side of the Bilstein sticker - is this where I need to move it to? Or am I looking in completely the wrong place?

 

Thanks for your help.

 

Edited by - clarkey on 16 Jan 2002 19:03:25

[Peter Carmichael]

The 300lb/in springs are twice the stiffness of the standard spring. With the same load on them, they will move half the distance. You are fitting them to the same dampers and you are not changing the open length of the damper (although you can do - I will come to that). On top of all this, the spring free length is an inch and a half longer.

 

You need the loaded length of the damper to be the same as it was before to get the same ride height. The load on a front wheel is about 120-140kg - call it 276lbs. This 276lbs is applied by the leverage of the wishbone suspension (ratio of 1.63:1) so the spring has to resist 450lbs. With a standard spring this means that the spring compresses 3 inches. With the stiffer spring, it compresses 1.5 inches.

 

This means that you need that you need to move the spring platform about 3 inches, to take into account the extra free length and the extra stiffness.

 

By the time you move the platform 3 inches, you will have no end load on the spring. It will go slack if you get the wheel unweighted - this is unsafe and needs a solution (or luck). Lockwire or tywraps can hold everything in place, but the real solution is a helper spring.

 

The alternative is to remove the spacer from just beneath the eye on the damper piston. This shortens the open length of the damper by ~1 inch and this will be the inch taken out of the slack on the spring. This does however stop the bumpstops from doing anything until well after your sump has ploughed a neat furrow.

 

The Caterham supplied spring doesn't actually fit Caterhams. To do it properly, you source a spring from another supplier with a shorter free length and fit a flat helper spring. It is quite brave to be attempting this without adjustable platforms - many take problems like this to the likes of James Whiting and they just sort it out, machining new grooves in the damper if required.

[clarkey]

But I have got adjustable platforms......

[Lawrence_Z]

I had some more grooves turned in the dampers at 15 mm spacing

 

Lawrence smile.gif

[Peter Carmichael]

That makes life easier. To get more space you can get rid of the lock ring. They never move of their own accord anyway and you can mark the position if you are worried.

 

The problem you have is that you will have to set the spring up slack at full droop. The open length of the damper is also too long.

 

So for quick and simple... remove the apacer, remove the lock ring, wind back the platform until slack , and lockwire or tywrap the platform to the spring so it doesn't all collapse on you.

 

Proper version... get a shorter 300lb/in spring from another source, get a helper spring (40lb/in) and go from there, keeping the spacer in play.