The standard S1 Exige springs are actually Eibach too.
Some springs have windings closer together towards one end so that the spring rate rises as it is compressed. What happens is, some of the coils come into contact with one another and bottom out which creates a shorter length of working spring, stiffening the car up as the ride height lowers. These are, surprisingly, called rising rate springs. If you have a car creating downforce then the wheel frequency (the natural resonant frequency of the wheel � which is what you are changing when you change the springs) is reduced as the speed increases. Rising rate springs keep things in check. There are various other situations where you might choose a rising rate spring and it is also possible to have a falling rate spring if you have suspension with rockers although this is a pretty unusual setup.
I recommend Eibachs because they are a very good quality spring made to very exact tolerances. If you buy a 400lb spring it will be exactly 400lb and you won�t have to worry about it sagging, shrinking or the rate changing over time. I have seen some pretty shabby looking springs coming off racing cars before and a knackered spring can really upset a cars handling.
600 & 650 is still doable on the road, but in the wet you really need to run the dampers much softer and also to set the front antiroll bar on its weakest setting, whcih I didn’t do, hence Ian’s quite correct assessment !!
you also have to remember that Guy has done a lot of work with the Nitrons valving and spring rates for elise/exige and he recommends 325/400 for starters as a road/track compromise for exige which (he says) works pretty well… and as Randy says… its more than twice your current standard spring rate.
Remember that what matters is wheel rate, rather than spring rate, and for cars where the damper is not vertical, (like ours) the effect of the spring is diluted even more, perhaps by another 25%…
not sure what you mean by diluted but this will mean that its even harder to compress the springs because you are only getting a component of the cars weight actually compressing the spring rather than if the spring were in the vertical plane where all the force would go into compressing the spring.
When the damper is not vertical the car has more leverage on the spring, and thus reducing its effectiveness…
So if the car is pushed down one inch, the spring perhaps only compresses 3/4 inch…
That make more sense??
That�s true but not too relevant as you just fit stiffer springs to compensate. What is more of a problem with setup’s like our is that the mechanical advantage exerted on the spring drops as the spring compresses due to the change in geometry - another reason for a rising rate spring. The greater the angle of the spring/damper the greater this effect is. The general rule is to get the spring/damper as vertical as possible when mounting from the wishbone to minimise and wheel rate changes under compression.
So if the car is pushed down one inch, the spring perhaps only compresses 3/4 inch…
The main reason for this is not down to the angle of the damper but the position of the lower mounting point relative to the wheel. i.e. the ratio of distance along the lower wishbone.
Just for info, way it’s calculated is to take the damper angle from vertical (lets say 45 degrees) that equals a ratio of 0.707 (cos of 45) so a 400lbs spring actually exerts 282lbs in the vertical direction. If the damper is mounted half way along the wishbone the actual wheel rate works out at 70lbs-in. The Exige is obviously very close to the outer joint so will have quite a high wheel rate, probably close to 250 for a 400 spring, may have a got at calculating it sometime.
Don’t know many cars with dampers so close to horizontal, actually the small Peugeots have very large angles on the rear IIRC.