Uprated front springs?

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NickC
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Uprated front springs?

Post by NickC »

I have now obtained a few weight figures for the Excel which indicates that the SA was 16% heavier than a Base Excel. This suggests that the front springs rates should be uprated by at least that amount. Lotus compensated for this by adding 6mm spacers.

What I would therefore like to do is to increase that rate of these by 20% and remove the 6mm adjustment spacer.

Question is can anyone tell me what length of spring would be required to make the car sit at the correct ride height or just slightly, say 1/4", below?

I would like to stick to 4 1/2" springs as at present if possible rather than going to 2 1/4" ones which I understand give a harsher ride for the same rate.

Any ideas how to calculate this?

Nick

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mds666
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Re: Uprated front springs?

Post by mds666 »

y?

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Re: Uprated front springs?

Post by NickC »

mds666 wrote:y?
Too much roll at the front around corners for my preferences, the front of an SA just feels a little bit too soft. Also the SA seems to knock out front springs rather quickly; removing the 6mm spacer and lengthening the spring slightly might help them last a bit longer.

Had the springs been uprated from Base by the same amount as the extra weight of the vehicle no doubt that would have been fine, but they weren't.

Nick

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dpr59
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Re: Uprated front springs?

Post by dpr59 »

No spacers on mine.
A

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mds666
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Re: Uprated front springs?

Post by mds666 »

i would suggest going for coilovers if you want to mess with spring rates as the standard spring size will cos a fortune to have someone to make you a one off... well 2...

this however will have a limited reaction to the roll rate, for this you will need a custom arb and/or drop links again this will not be cheap and you can dial in all sorts of odd efects...

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Lotus-e-Clan
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Re: Uprated front springs?

Post by Lotus-e-Clan »

Also grip levels will change for the worse if you stiffen up too much as weight transfer in a corner to the outside tyre is reduced.

For example the Clan (my other toy car) base springs are VERY soft: 68Lb front, 210 Lb rear, with no anti roll bar.
OK, the kerb weight is only 580 Kg and it's a rear engined car, so everything is relative.

These settings were developed by Lotus engineers (Paul Haussauer. Brian Luff and John Frayling) to give the best ride, handling and grip compromise using 155/80/12 road tyres on front swing axles with semi trailing rears.

The standard Clan rolls alarmingly when thrown into a bend but just grips and grips. 8)

Clan owners who stiffen the springs without modifying other suspension settings find roll is indeed reduced but the grip is worse especially in the wet at relatively slow speeds. :shock:

Excel grip/suspension geometry cannot be directly compared to the Clan especially because of the Clan's rear engine design but the principle relationship between grip, weight distribution, and suspension settings remains the same.

However, I expect Lotus didn't foresee SA owners exploring the limits so a quick fix to ride height made economic sense. :mrgreen:

If you do significantly stiffen the springs you could also consider changing the tyres to something with more wet grip to compensate. :wink:
Peter K

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Re: Uprated front springs?

Post by bash »

The spring rate can be calculated, see this link
http://www.pagedezigner.com/bluecoil/rate2.htm

Bash
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NickC
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Re: Uprated front springs?

Post by NickC »

dpr59 wrote:No spacers on mine.
Are you sure about that. They are fitted on the top end of the spring inside the chassis spring housing, impossible to see without removing the springs.

Nick

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Re: Uprated front springs?

Post by Pete Boole »

NickC wrote: They are fitted on the top end of the spring inside the chassis spring housing, impossible to see without removing the springs.

Nick
Are you talking about the rubber mounting buffers?

Pete

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Re: Uprated front springs?

Post by NickC »

Pete Boole wrote:
NickC wrote: They are fitted on the top end of the spring inside the chassis spring housing, impossible to see without removing the springs.

Nick
Are you talking about the rubber mounting buffers?

Pete
Pete,

A manual Excel has:
Insulator, Spring to Chassis - B075C0129Z

whereas an Automatic has this instead:
Spacer, 6mm, Front Spring to Chassis - A089C0789F.

They were only fitted on the SA due to the extra weight.

This begs the question, how thick is the Insulator compared to the 6mm of the Spacer?

Nick

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