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Spring and damper recommendations for 86 turbo - Suspension/Brakes/Wheels/Hubs/Steering/Geo - The Lotus Forums Jump to content
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Spring and damper recommendations for 86 turbo

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I am planning to replace the springs and dampers on my 86 turbo while I have the engine out for modifications. I am considering using lotus bilstein damper eibach spring sets but am having trouble getting anyone to supply both fronts and rears. Can anyone recommend good quality alternatives? I also plan to fit a full set of poly bushes while I have the car in bits and would welcome your input if you have fitted these.

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Andrew, I think Bibs has these in the Online Shop? Not sure. Can't check it at the moment as it is Under Construction :construction:  But hopefully Bibs will see this and reply.

 

Have you tried Lotus directly?

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Yes Bibs supplies mine3-4 years ago. 

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Ive got the Eibach and Bilstein fitted as well as the Lotus poly bushes.

 

Buddsy

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What did you think of the Polybushes? Good fit, ride well?

Trevor.

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Er...to be honest I didnt drive it before so cant really compare. Also Im on 30year old tyres so have been a bit reluctant to push too hard but feels pretty good.

 

Buddsy 

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Thanks for the replies I"ll wait to see if Bibs can supply them via online shop.Ido have a set of new AVO shocks for the rear but would prefer to fit Lotus developed suspension.

Andy

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If for some odd reason the shop doesn't have any left, you may consider ordering a custom set of springs from here. They claim to produce springs in original, OEM spec for numerous makes and models, including Lotus: 

 

http://www.coilsprings.co.uk/classic.html

 

Very polite, amiable customer service, and reasonable cost (around 185 GBP for four springs, plus shipping, at least for a G-Esprit). 

 

Cheers,

 

Scott

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I had PUK yellow poly-s at the front and they desintegrated. I had no idea why...

 

Here is a good explanation from Tim Engle:

 

Note that the early Turbo chassis (pre-SE) used an anti-dive suspension geometry which also contributed to pitch control. It also incorporated a built-in pivot axis misalignment for the front arms which resulted in the bushings being put into a bind condition as the suspension moved off the normal ride height position. By doing that, and carefully balancing bushing durometer, they were using bushing compliance to fine-tune overall wheel-rate in as the suspension moved.
From the SE onward, the chassis used pro-dive (opposite of anti-dive) and no bushing compliance geometry. So, directly comparing the effects of spring rates between early and later models isn't really possible.

For the X180R, Lotus actually welded the old anti-dive/ bushing compliance "T" cross-member to the SE chassis because they wanted to better control pitch in the race car. Lotus introduced its own polybush set. Theirs was unique compared to most aftermarket bushings in that Lotus kept the durometer down in a range similar to the original rubber bushings. Generically speaking of all applications, most aftermarket polybushings are considerably harder than stock.  Their selling-point is to firm-up the suspension for better performance.

However, in a system designed to require compliance, something has to give. In a contest between steel and urethane, I'd bet on the steel bits surviving, and the urethane bits taking the brunt of the abuse. I doubt that the polybush vendors who recommend hard bushings for the Esprit are aware of the Lotus design's offset axis, and it's reliance upon compliance.
*~*~*
The Esprit (Europa, Elite-Eclat) trailing arm rear suspension has a similar but different requirement for compliance. The hub carrier doesn't just go straight up and down. It's hard-bolted to the end of the trailing arm, which swings in an arc in side view.  If the trailing arm swings down 10 degrees, then the hub carrier rotates 10 degrees as it goes down. As a result, the studs for the shock and lateral link also rotate 10 degrees, while the bushing eyes in the shock and lateral links do not. That creates a bind. Both the Lotus OEM rubber bushing and Lotus' own polybush kit use a softer durometer that provides sufficient compliance to absorb the hub's rotation from full droop to full bounce. It's a requirement, not an option.
If you put hard polybushings in the rear suspension, you'll create a similar bind between steel and urethane. A hard urethane will lose, while a softer, more compliant urethane will survive. Rubber is particularly good at compliance.

Have you ever replaced the Esprit's rear shocks?  With the suspension at full droop, there's a significant miss-alignment between the stud in the hub carrier and the bottom eye of the shock.  To ease assembly, use a floor jack to raise the hub carrier to normal ride height position with the stud horizontal.  Then it's necessary to compress the spring in order to shorten the shock to meet the stud.  Then they align and slide together easily. It's variation on the same issue... at full droop the stud is no longer horizontal.

Polyurethane is an acceptable bushing material for rubber, especially if the OEM rubber parts are unobtainium. The point to all this is to maintain a similar durometer for the Esprit's 'required' compliance.

Polyurethane is available in grades all the way from rock hard to squishy GummyBear/ fake bait soft. To some, "urethane" automatically means "harder" for suspension bushings. No! It doesn't have to, and harder is a poor choice for the Esprit's suspension.  As I mentioned previously, the rubber in the stock Esprit bushings is about 60 Shore A durometer.  Ball park +/-

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Here is a good explanation from Tim Engle:

Thanks for that, very informative.  :thumbup:

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FYI:

SPRINGS:

86,87,88 (17%anit-dive),

Front: Rate – 22.8 N/mm / 130 Lb/in, Free Length – 369mm, Static Length – 203mm, ride hgt 170mm

Rear: Rate – 27.5 N/mm / 157 Lb/in, Free Length – 334mm, Static Length – 205.7mm, ride hgt 170mm

SE (22% pro-dive)

Front: Rate – 29.1 N/mm /166 Lb/in, Free Length – 372mm, Static Length – 219mm, ride hgt 190mm

Rear: Rate – 27.5 N/mm / 157 Lb/in, Free Length – 347mm, Static Length – 218mm, ride hgt 170mm

S4/S4s

Front: Rate – 41 N/mm / 234 Lb/in, Free Length - N/A, Static Length – 214mm

Rear: Rate – 45 N/mm / 257 Lb/in, Free Length - N/A, Static Length – 227mm

Edited by MrDangerUS

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When changing springs you have to calculate their required length to determine the car ride height. My preference is 165mm front, 170mm rear.

You need a static pr-eload weight value, which equals corner weight value (usually, front =~630-670 Lbs).

Divide it by a spring rate = static pre-load deflection, which determines static vehicle height. Split the shock travel range 60%/40% (bump/rebound) and calculate the spring length to dial this value. If your car has adjustable perches = it's not that difficult. With stationary perches, you my have to go trough a "trial and error" fitting.

Same procedure for the rear.

It help if you can put your car on the Scales.

IMG_2351.JPG

Edited by MrDangerUS

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But you also have to take into account that the spring has a lever attached to it in the form of the lower link extending past the spring platform and also movement is not parallel to the direction of compression. It would be very difficult to calculate unless the whole of the suspension geometry were known.

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Yes, you are right. If you want to alter the spring rate dramatically (more than 5-10%), you have to calculate wheel ratios and many other parameters.

However, if you want to stay close to  your OEM rates, just buy springs from eBay or Amazon(they carry Eibach-s) with all dimensions as your old one.

Shoot for the spring rate value close to the stock part (+ side is OK) and calculate the required spring length in regards to the desired ride height (as in my previous post).

Here is an interesting discussion:  http://www.lotustalk.com/forums/f164/lower-cost-bilstein-option-123221/

If you have adjustable perches, it is easier to fine tune them after the installation.

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Has any Turbo HC owner fitted the SJ Sportscars Adjustables? I want a lowered look to my car and interested to see how much they can drop safely in their lowered setting.

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You getting your car back on the road Neil?

The earlier cars are much lower than the later ones.

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