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Spring Length Vs Damper Travel

Motorsport Wheel Alignment Fundamentals

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I've watched the majority of the videos now and I'm in the middle of correcting my suspension setup.

In doing so I've purchased a front and rear RCA kit from a company called Honed Developments in Australia (Honda double wishbone suspension specialists).

With this kit I need to increase my spring rate for the front of the car. Unfortunately the manufacturer of my coilover doesn't make the required spring rate in the same free length of 200mm that the coilover currently uses.

They've offered me the closest length spring at 180mm in the required rate I need.

My question is, with a 20mm shorter spring am I going to see any reduction in available bump/rebound travel of the damper?

It took me a while to grasp the correct coilover adjustment method, so as I understand it, with the shorter spring, I would raise the spring perch to hold the spring captive and this would mean my ride height will be 20mm higher than the current setting?

To remain at the same height with the spring perch I would have a spring that isn't captive at full droop? Surely though at 20mm difference, that isn't a large enough gap to use a helper spring setup?

Little bit confused as to whether or not I should turn down the 180mm springs or find an alternative in 200mm.

I'd be very surprised if 20 mm is going to make any significant difference to the suspension travel. the only potential issue would be if the spring became coil bound prior to reaching full bump travel. That's unlikely to be an issue with a spring that's 180 mm long.

The shorter spring length will require you raise the spring platform to achieve the same ride height, however that doesn't mean your ride height will be higher - You can still set it to whatever you want. The spring may be non-captive at full droop but this will depend on the spring rate, weight on that corner of the car, and the desired ride height. Depending on your local rules any amount of free play at full droop may be illegal. By the time you add a keeper spring the overall length is likely to be almost identical to a 200 mm spring.

There should be no problem using a 'helper' spring to ensure the coils stay captive on their seats - the thought of none-captive springs gives me the heebie-jeebies as that's just an accident waiting to happen!

What diameter springs do your coil-overs use as we may be able to source what you need - come to that, what's the spring rate*? Most springs are one of 4 standard internal diameters and they are basically interchangable from different manufacturers - if you can't find what you need from one, a different supplier may have just what you want.

As Andre said, with a 20mm shorter spring, you'll be moving the lower seat up 20 mm so the top of the spring will be in the same place as a 20mm longer one with the seat set 20mm lower.

*remember, the rate remains the same regardless of length - a 180mm spring and a 200mm spring, both with a 10 kg/mm (some may be N/mm, or lbs/inch, but same principle) rate will both compress 25mm under a 250kg load.

Thanks for the reply guys.

So the coilovers are manufactured by a company here in the UK - Meister R and they use a 62mm ID spring. I've been recommended a 16kg spring by Honed Developments to use with their products, and the closest spring in 200mm I've been able to find are Eibach springs in 2.25" ID which equates to 63.5mm so slightly bigger.

Meister R also mentioned about spring bind with the shorter spring but with the shock absorber length for my set said it won't be an issue.

I guess without measuring my base ride height setting with the spring removed from the coilover to achieve the optimum bump/rebound ratio I won't know if the shorter spring is going to need a helper spring?

A helper spring is used when the fully extended spring length is less than the distance between the upper and lower spring seats at full damper extension, with the adjustable seat set to the desired ride height.

As you say, without knowing the exact setup you're going to be using, it may be a case of trying it and seeing what happens.

Sort of the sme thing with the spring bind, it will depend on how the spring is formed to get that rate - more coils will bind earlier, fewer later, round earlier, square or oval later, threre are even slight differences in the steel alloys used or for the truely flush, titanium, which may affect the spring properties.

There is also a company making spring disks that can be mixed and matched for even finer resolution of the spring rates and lower mass. For those interested - https://www.compositesworld.com/articles/carbon-composite-spring-big-performance-small-package

Oh, which reminds me - this may be a good point to re-inforce the correct terminaology -

Many people incorrectly refer to the dampers as 'shock absorbers' - dampers are used to 'dampen' or reduce the spring oscillations (bouncing) that results from wheel or chassis movement. Fun thing to do in a SAFE environment is to drive a car with the dampers removed, or set to softest position, over undulating and/or bumpy surfaces, then do it again with the dampers working.

The actual 'shock absorbers' are the springs, which are used to absorb the impulses passed from the wheels to the chassis from bumps and/or from chassis movements through to the wheels, etc.

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