Springs and dampers - 1978 S1 Elite

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DavidOliver
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Re: Springs and dampers - 1978 S1 Elite

Post by DavidOliver »

Perhaps the term Coilover has come from USA where shortenings of made up words leads us not to know exactly the meaning.
Many cars had springs(coils) located in a different position to the damper (shock absorber in English, why have a wet shocker?)
It was found you get a better reaction to have the spring around the shocker, which makes sense, so a coilover mod was carried out
to improve cars with non-concentric set-ups, a common feature of American cars. Leaf spring to coil spring conversion.
The Elite/Eclat/Excel has only had coilovers (concentric spring to shock absorber........ in English).

Dave the cog.

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theelanman
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Re: Springs and dampers - 1978 S1 Elite

Post by theelanman »

Pete Boole wrote:
Sun Jun 28, 2020 06:48
Mine measured 142lb/inch at the front and 110lb/inch rear.

Pete
Pete
Did you happen to note the standard lengths?
Cheers
G

richardw
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Re: Springs and dampers - 1978 S1 Elite

Post by richardw »

Pete Boole wrote:
Sun Jun 28, 2020 06:48
Mine measured 142lb/inch at the front and 110lb/inch rear.

Pete
A few years ago I did some tests at Lotusbits with Mike Taylor. We took some used Elite springs and measured them on his press. Here are the results, together with a comparison from the spring rates published in Autocar at the car's introduction.

Spring.....Unladen length (in)....Tested lb/in....Autocar lb/in
Front, a/c........................17.25.....................144.................145
Front, non a/c.................18.75.....................107.................105
Rear................................15.75.....................110.................115

As you can see, there are two types of front spring depending on whether the car was fitted with a/c or not. It's also interesting to note how little degradation in spring rate had taken place over the years.

Cheers, Richard
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theelanman
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Re: Springs and dampers - 1978 S1 Elite

Post by theelanman »

So just looking at that.......
For example......
As mine is a std car without a/c.....I could almost take the std springs out and swap them for standard a/c rated springs............
I could then get a couple of rear springs made.......for the rear........at 145lb per sq in and 14.25in long........
Altho that might drop the car too far for me......
Lol

Pete Boole
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Re: Springs and dampers - 1978 S1 Elite

Post by Pete Boole »

Fitting springs from a car with a/c to one without will raise the car, not lower it. 145 lb/inch on the back will probably lock the suspension at full height! You need shorter springs with the same rate that you have now to lower the car.

Don't get me going on which part of the suspension absorbs shocks, and which part damps the oscillations of the spring!! :wink:

Pete

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Lotus-e-Clan
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Re: Springs and dampers - 1978 S1 Elite

Post by Lotus-e-Clan »

Also if you go too hard at the rear it will swap ends at the first roundabout (oversteer). :shock:

Rule of thumb:
Too hard at rear (or too soft at front = eg non-A/C springs when you have A/C) = oversteer
Too hard at front (eg using A/C spring rate on the front when you haven't got A/C) = understeer

Obviously damper rates will factor into the likelihood of understeer/oversteer too.
Peter K

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theelanman
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Re: Springs and dampers - 1978 S1 Elite

Post by theelanman »

Sorry......ignore me.......im talking rubbish......longer spring lighter load.......

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theelanman
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Re: Springs and dampers - 1978 S1 Elite

Post by theelanman »

Mmmmmm.......
So coilovers......dampers where the sprung height can be modified and preloaded......so maintaining the same spring rate....?????

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Re: Springs and dampers - 1978 S1 Elite

Post by richardw »

I really wouldn't go for coilovers on the Elite, where relatively soft spring rates and long travel determine ride quality. If you must, go for slightly shorter springs and slightly higher spring rates (as you won't have as much suspension travel) then you will still be using the standard spring mountings rather than feeding everything through the shock absorber mounting which will make the ride harsher. It would be worth calculating the corner weights on your car (from the front/rear weight distribution and the vehicle weight) and the wheel deflection for each inch of spring deflection. For this you need to check the geometry of the suspension and find out the leverage the wheel deflection exerts on the spring, then (I think) square the leverage. I can dig out the formula later when I have time!

Cheers, Richard
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Re: Springs and dampers - 1978 S1 Elite

Post by theelanman »

Richard....
that'd be wonderful if you get chance
Thanks in advance
Gareth

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Re: Springs and dampers - 1978 S1 Elite

Post by TrevorK »

Yes, the spring rate is related to the wheel rate by the square of the lever ratio between spring mounting to the wishbone and the wheel pivot length as the movement of the spring is reduced by the lever ratio when the wheel goes over the bump but, as the torque is the same in both places, the load on the spring goes up be the ratio. So wheel pounds per inch of wheel movement becomes spring load (= wheel load x lever ratio) over spring compression (= wheel movement / ratio). This expands to (wheel load/wheel movement) x ( lever ratio x lever ratio).

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Re: Springs and dampers - 1978 S1 Elite

Post by richardw »

Thanks Trevor, good explanation!

Here is a worked example Mike Taylor provided me with to calculate wheel rate:

The spring rate is not force - it is force per distance - Newtons per mm or lb/inch

Both force AND distance are affected by the leverage hence the square term

200lb spring with 2:1 lever ratio to the wheel.

Apply 200lb to the wheel and the spring will compress 2 inches because of the 2:1 lever ratio

This means the wheel will move 4 inches when the spring compresses 2 inches due to the lever ratio

So 200lb moving 4 inches gives a wheel rate of 50lb/inch - not 100lb per inch

On the Elite, I think that the springs are mounted very close to the hubs, so the lever ratio is more like 10:9

Cheers, Richard
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