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Can someone double confirm the stock front spring rates for my 84 turbo domestic? 115lb's?

Also are they 14" springs?

I don't have adjustable platforms and do want to lower the ride height slightly, with the sagging stock springs its too high unloaded but probably about right fully loaded...but way too bouncy.

If I change to stiffer springs I should shorten the height to compensate but by how much if I stiffen the springs?

I hope I haven't confused you all??

Robert


Robert Costa
1984 Turbo Esprit
Very Black!
2004 Lotus Elise
Quite Green! gone :-(

1977 S1 Esprit, in bits

1998 Lotus Elise S1, Azure Blue
Sydney, Australia

“The parts falling from this car are examples of the finest British craftsmanship”

Recommended procedure before taking on a repair of Lucas equipment: Check the position of the stars,kill a chicken and walk three times clockwise around your car chanting:" Oh mighty Prince of Darkness protect your unworthy servant.."

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I have got the spring rates for the S3 (no air con) at work somewhere, I'll dig them out for you tomorrow, but 115lb and 14" sounds about right for the fronts.

Stiffening the spring rate and then trying to guess how much to shorten them to get a reduced ride height is going to be a bit hit and miss.

If you get it wrong you are stuck with them.

If you speak to a company call coil spring Clicky they have coil data for all the Esprit models so they will have the correct lengths and rate for your car, they can even make for you. They did a good job of mine.

Hilly


1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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I have got the spring rates for the S3 (no air con) at work somewhere, I'll dig them out for you tomorrow, but 115lb and 14" sounds about right for the fronts.

Stiffening the spring rate and then trying to guess how much to shorten them to get a reduced ride height is going to be a bit hit and miss.

If you get it wrong you are stuck with them.

If you speak to a company call coil spring Clicky they have coil data for all the Esprit models so they will have the correct lengths and rate for your car, they can even make for you. They did a good job of mine.

Hilly

I know I'm treading into unknown territory!

I don't quite understand why the stock spring rates are so soft. I'm guessing there's a balance between the stiffness and the un-sprung weight...after all, if the springs are stiff enough the whole car is the un-sprung weight :ermm: . My elise runs 350 lb front springs on 800kg car so you can see why 115 seems a little light.

Robert


Robert Costa
1984 Turbo Esprit
Very Black!
2004 Lotus Elise
Quite Green! gone :-(

1977 S1 Esprit, in bits

1998 Lotus Elise S1, Azure Blue
Sydney, Australia

“The parts falling from this car are examples of the finest British craftsmanship”

Recommended procedure before taking on a repair of Lucas equipment: Check the position of the stars,kill a chicken and walk three times clockwise around your car chanting:" Oh mighty Prince of Darkness protect your unworthy servant.."

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Yes the spring rate does seem low, but it all depends on the pre-load.

If you have a 115lb/in spring and you load it with 350lb (about the weight of a front corner of an Esprit) then it will compress 3", add another 115lb (say going over a bump) and it will squish up another 1"

With your Elise, again start with 350lb and the suspension will compress about 1", add another 115lb it will only compress an extra 1/4".

So you see the spring rate defines the suspension travel over a certain condition.

The above example shows that the the Esprit's suspension has a much longer bump travel which makes it a more comfy ride compared to the Elise.

You will find the Esprit's springs are a fair bit longer than those on the Elise.

The bouncy bit of the suspension travel is controlled by the damper, if you harden up the compression rate then the ride will turn very aggressive, but the wheel will be well controlled over bumps. Soften the damper up and the ride will be more comfy, but the car won't hold the road anywhere near as well as the wheel is bouncing up and down. This is where low un-sprung weight helps as it allows soft spring and damper rates whilst keeping the wheel well controlled.

As usual with engineering solutions, every thing is about balancing the elements to get the best compromise.

When I get into work I'll dig out those spring details for you.

Hilly


1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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Here is the data from my 84 car

SPRINGS- front/ rear

Length @ Ride HT- 8.5/ 9.0

Length @ Full Droop- 10.3/ 11.0

Length @ Full Comp- 6.5/ 7.0

Number of Coils- 10/ 8

OA Diameter- 4.5/ 4.0

Wire Diameter- 12mm/ 12mm

Free Length- 14.0/ 13.4

Rate (lb per inch)- 125/ 155

Spring/Wheel Motion Ratio- 0.69/ 0.93

My theory on the light spring use is perhaps Lotus used a light spring to limit load transfer (hence flex) into their somewhat "soft" chassis.


If you set no goals you shall surely reach them..

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Finally found the spring data for my S3 which is without air con.

Front free length 14.0" rate 110lb ID 3.47"

Rear free length 12.8" rate 140lb ID 3.183"

Hope this helps.

Hilly


1981 S3 4.2 V8 6 speed (The Mutant)

Mutant V8 Conversion Thread

Knowledge is power .................... apparently.

 

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Thanks all. Good stuff.

I'm going to check the corner weights and do some math to estimate the new spring rates and see.


Robert Costa
1984 Turbo Esprit
Very Black!
2004 Lotus Elise
Quite Green! gone :-(

1977 S1 Esprit, in bits

1998 Lotus Elise S1, Azure Blue
Sydney, Australia

“The parts falling from this car are examples of the finest British craftsmanship”

Recommended procedure before taking on a repair of Lucas equipment: Check the position of the stars,kill a chicken and walk three times clockwise around your car chanting:" Oh mighty Prince of Darkness protect your unworthy servant.."

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Finally found the spring data for my S3 which is without air con.

Front free length 14.0" rate 110lb ID 3.47"

Rear free length 12.8" rate 140lb ID 3.183"

Hope this helps.

Hilly

Interesting comparison my FED to your UK spec. Mine were measured from the car... yours too... or are they a technical spec?

Could explain the higher (ugly) ride height of the Fed cars...

Edited by f1karting

If you set no goals you shall surely reach them..

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I know I'm treading into unknown territory!

I don't quite understand why the stock spring rates are so soft. I'm guessing there's a balance between the stiffness and the un-sprung weight...after all, if the springs are stiff enough the whole car is the un-sprung weight :devil: . My elise runs 350 lb front springs on 800kg car so you can see why 115 seems a little light.

Robert

The important thing is the wheel rate, not the spring rate. The two are related by the square of the lever ratios between the spring and the wheel about the fulcrum. So a car with pushrod suspension and a small rocker will have a sky-high spring rate while a car where the spring connects to the hub will have a much lower spring rate to achieve the same ride quality.

I like the softer ride of the Esprit over the rock-hard ride of the Elise I rode in but, as Hilly so rightly said, the dampers have a big effect. It needs soft bump damping but stiff rebound control to stop it pogoing down the rode. However, if they are too different, the car will lower itself as it rides along a bumpy rode because the soft bump allows the wheel to rise more than the hard the stiff rebound lets it fall before it hits the next bump.

Anyway, I would check the dampers before undoing all the good work the Lotus Engineers did on the suspension.


S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE

 

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I saw this web posting

http://www.shadeone.com/modifications.html

He runs front rates lower than rear, which makes sense in the mid-engined car, although his values are higher than SE' (if the link below is correct).

On the web, there are several different opinions, all of them hae front rates higher than rr. What is the reason for that?

http://www.thelotusforums.com/forums/index.php/topic/35553-spring-rate/page__p__314885__hl__%2Bspring+%2Brate__fromsearch__1#entry314885

It does not make sense to run such stiff front springs. Am I missing something?

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It does not make sense to run such stiff front springs. Am I missing something?

Mechanical advantage. The rear springs are close enough to 1:1 but the front ones, being mounted in from the wheel are less. You could calculate its ratio by measuring the distance of the arm and where along that arm the spring is mounted. My guess is about 4:5.


DanR

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Interesting comparison my FED to your UK spec. Mine were measured from the car... yours too... or are they a technical spec?

Could explain the higher (ugly) ride height of the Fed cars...

i seem to recall, FED turbo front rates should be the different as an Euro N/A S3. the FED S3 turbo is higher rated if memory serves

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Here is an additional intel, FYI:

 

(88 Federal ?) Non-SE 89. (17% anti-dive geo),
Front: Rate– 22.8 N/mm / 130 Lb/in, Free Length–369mm (14.5”), Static Length– 203mm (10”), 585# preload, ride hgt 170mm
Rear: Rate– 27.5 N/mm / 157 Lb/in, Free Length–334mm (13.15”), Static Length– 205.7mm (8”), 808# preload, ride hgt 170mm

17 mm dia. front anti-sway bar

 

 

89+ SE (22% pro-dive geo)
Front: Rate– 29.1 N/mm /166 Lb/in, Free Length–372mm (14.6”), Static Length– 219mm (8.62”), 992# preload, ride hgt 190mm
Rear: Rate– 27.5 N/mm / 157 Lb/in, Free Length–347mm (13.7”), Static Length– 218mm (8.6”),  800# preload, ride hgt 170mm

17 mm dia. front anti-sway bar

 

 

S4/S4s
Front: Rate – 41 N/mm / 234 Lb/in, Free Length - N/A, Static Length– 214mm (8.43”)
Rear:  Rate – 45 N/mm / 257 Lb/in, Free Length - N/A, Static Length– 227mm (8.93”)

15 ? mm dia. front anti-sway bar

 

The front damper platform height for each of these measurements is 59mm. The rear platform height is 115mm. The extended/compressed length for the front is 12in./10in., and the rear is 16in./12in.

 

Also, see:

http://www.lotustalk.com/forums/f164/lower-cost-bilstein-option-123221/

Here are the part numbers from Bilstein

24-020541 rear   Corvette C4 rear Konis Red/ Special or Yellow/Sport.

24-187824 front, Fiero front Konis Red/Special

 

Suspension  geomery could be modelled with Susprog 3D  http://www.susprog.com/susptype.htm

Edited by MrDangerUS

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