Springs

[julians]

I may be dreaming this but I'm sure I heard someone say that you can tell what weight of spring you have by the colour of them, does anyone have a list of what colour means what weight?

 

Juts for reference I have blue springs on the the front, with red on the back, both on bilstein dampers.

 

Whilst were on the subject what do the colours of the front arb match up to.

[Andrew Dent]

This may not help, but green are 250 lbs

 

Andrew

[Peter Carmichael]

The green front springs sourced from Caterham are 2.25in diameter (not 1.75in like the black ones, so you will need replacement end stops for the dampers) and 250lb/in spring rate. The green rear springs sourced from Caterham are 170lb/in IIRC which is too stiff IMO, giving too harsh a ride, poor traction over bumps, but negating the need for a rear ARB.

Recent black front springs are 150lb/in which is arguably too soft - the worst manifestation of this softness is the ride frequency of the front suspension - this particularly affects the pitching activation of the suspension with the onset of heavy braking.

Caterham have supplied red 300lb/in springs for the front, which were commonly used on the k-series supersports race cars. These should probably be partnered with a reduced stiffness ARB (5/8in). This is where Juno might recommend going as far as 350lb/in or 400 lb/in with the possibility of reducing to a 1/2in ARB.

 

The progressive rate rear springs are a very good idea and they work well, although they are implemented in a cheap fashion. They allow extended droop travel which improves traction over bumps and crests, while allowing low ride heights.

 

I have also seen blue and yellow, but they date from before I became aware of the boingy bits on Caterhams. Judging spring rate by colour depends on the source of the springs. The method is only reliable for the standard springs that Caterham have supplied over a consistent period in their production history.

 

It is impossible for the same dampers to perform optimally over a range of spring rate from 150lb/in up to 400lb/in - at one or other extreme of the range the damping ratio will be compromised. The current spec Bilstein dampers don't do badly and I would hesitate to recommend any alternative without access to a damper dynamometer to compare to the Bilsteins as a baseline.

 

Compliance in the suspension is another area of interest. Compliance is necessary to reduce the peak loads seen by the suspension pickup points. Arbitrarily replacing bushes with spherical joints will eat into the safety margin in the chassis construction and lead to increased failure rates. No ifs or buts. It might be a matter of immaterial reduction in service life (i.e. 95% life of 200,000 miles reduced to 150,000 miles), but there will be a reduction. The Bilstein dampers are however over-generously bushed:

 

The sloping installation of the spring/damper units on the front suspension gives a mechanical advantage in the actuation of the dampers. The ratio of motion for a widetrack suspension is something like 1:1.64. For 1.64 inches travel at the wheel, the damper moves 1 inch. The effective spring rate at the wheel is given by multiplying the physical spring rate by the square of this ratio.

 

e.g. 150* 1/1.64 * 1/1.64 = 55.77 lb/in - this is why a recommended front spring rate is nigh-on double the rate of the rear springs (which are direct acting).

 

At the same time, the forces acting on the dampers are multiplied by this ratio. The high force also, by design consequence, tends to result in increased damper stiction, which is where the Bilsteins seem to be superior to many alternatives. If each front wheel is supporting 110kgf (1080N) of sprung mass, the force on the damper will be 1.64 * 110 = 180 kgf (1769N). This force is the static force on the damper bushes. Have a look at how deformed these bushes are at standstill. The dampers have also had to be valved to take account of the action ratio. This means that the dampers are set at a very high rate. The bushes also see these large damping forces and are further deformed accordingly. This deformation allows movement in the suspension to take place without the damper moving. The deformed bush stores energy. Having this energy being released without a corresponding damping effect ultimately compromises the quality of the tyre/road contact and reduces grip.

 

It is probably a worthwhile exercise to experiment by replacing the bushed eye on the damper piston with a rod end, halving the damper compliance.

 

The bushing of the front anti-roll bar is another obvious site of compromise, especially with the smaller diameter ARBs.

 

This is not to say that it would not be better to move to a completely re-engineered solution with re-assessed high speed and low speed bump and rebound damping rates, with spring rates and anti-roll bar rates analysed against modal suspension displacements and the distribution of the major masses and the anti-dive and camber compensating aspects of the suspension geometry and chassis stiifness. Just that, as with most things, the incremental returns diminish with increased input cost and effort.

 

[Mike Bees]

Don't rely on the colour. All the Suplex springs that DT sell are red by default, irrespective of their poundage.

 

Mike