Lotus Elan

Front Spring length for +2

PostPost by: therolfie » Tue May 17, 2016 10:08 pm

As the list title, what size front springs & rate to fit to Gaz adjustable platform units. I fitted 11" free length 140ibs springs but to get the correct ride height I have wound up the platforms, the impact of this is the springs are too close together so can't operate & bottom out! All help & ideas welcome. I did try to find specs before I fitted these units. :((
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PostPost by: therolfie » Wed May 18, 2016 7:29 pm

Ok so rung a couple of the usual suppliers today.

One suggested an free length of 9" & 175ibs

The other free length 12" & 150ibs

The original for the plus two was 14" & 110ibs

I will wait to see if people have experience with a good set up.

Thanks for any feedback of plus two use.
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PostPost by: rgh0 » Thu May 19, 2016 12:02 pm

mmmmm.... looks like most of the suppliers don't understand much about design of springs. i assume you want the same installed length as the original springs ? If that is the case then the next question is what style of spring you want.

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PostPost by: therolfie » Thu May 19, 2016 5:54 pm

Hi Rohan
I have GAZ shocks with adjustable platforms & in time will convert the rear to adjustable. I'm after a fast road car set up, but yes I want to be able to drive it without my teeth falling out! I have measured the gap whilst the car was jacked up & the platforms unwound. This was 27cms or about 10 1/2". Any thoughts? Thanks
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PostPost by: rgh0 » Sat May 21, 2016 6:02 am

The Plus 2 with its wider track and higher standard spring rate is much more suited to modern sticky tyres than the Elan. I run mine on the standard setup with Yokohama 165 x 13 / 60 A048R track day tyres for road use and find it fine with no real need to harden it up.

If I was going to set it up harder I would try around 140 lb/in front and 120 lb/in rears as a first step. I would probably also go up from the standard 3/4inch (19mm) front roll bar to 21 mm. All this make the handling a little sharper without making it so hard as to be uncomfortable on normal roads

Free length for same ride height with standard platform position would be 12.7 inch for fronts and
Free length for the rears would 14.3 inch. Installed length for these springs would be the same as the originals i.e. 8.6 inch front and rear

When fitting stiffer springs especially the fronts on a Plus 2 you always need to check coil bind height and ensure the shock hits the bump rubber before the coils bind. Most Plus 2 springs designs are very highly stressed so you need to buy top quality springs preferably "hot wound" to avoid rapid sagging of the suspension due to the front coil collapsing under stress.

If going to smaller diameter rear springs and the orginal Aeon rubber spring does not fit find an equivalent rubber spring that fits and fit the spacer like the later Plus 2 had.

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PostPost by: therolfie » Sat May 21, 2016 7:13 am

Thanks for the information, I will have another look at my plans and decide which way to go. I have found an old set of original front shocks so will fit these for now.
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PostPost by: vincereynard » Sun May 22, 2016 7:49 pm

Please shoot me down if I am wrong as this is something I have been trying to get straight for a while.

According to the manual the front spring is 14.19 / 8.6 Free / fitted. A the initial poster stated.

So this would give a preload of 14.19 - 8.6 X 110 lbs = 559lbs.

A 11in free length, fitted between the same damper seats would only give 11 - 8.6 (2.4) X 140 = 336 lbs.
To get a 559 lb preload the lower seat would have to be raised to compress a 140 lb spring 3.99 inches.

3.99 - 2.4 = an extra 1.59 inches. I. e. - most of the adjustment
OR to get the same preload, with a 140lb spring, it would need a free length of 12.59 inches.

Is this relevant??
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PostPost by: rgh0 » Sun May 22, 2016 7:59 pm

vincereynard wrote:Please shoot me down if I am wrong as this is something I have been trying to get straight for a while.

According to the manual the front spring is 14.19 / 8.6 Free / fitted. A the initial poster stated.

So this would give a preload of 14.19 - 8.6 X 110 lbs = 559lbs.

A 11in free length, fitted between the same damper seats would only give 11 - 8.6 (2.4) X 140 = 336 lbs.
To get a 559 lb preload the lower seat would have to be raised to compress a 140 lb spring 3.99 inches.

3.99 - 2.4 = an extra 1.59 inches. I. e. - most of the adjustment
OR to get the same preload, with a 140lb spring, it would need a free length of 12.59 inches.

Is this relevant??


Yes you are correct with the calculations and this is the problem with the original 11 inch free length springs fitted.

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PostPost by: vincereynard » Mon May 23, 2016 8:27 am

rgh0 wrote:
Yes you are correct with the calculations
cheers
Rohan


It had to happen sometime! :D

So before changing springs etc, the distance between the damper spring seats on the, fully extended, existing damper should be measured / established.
Which, presumably, should be the 8.6 > 9.0 inches mentioned in the workshop manual.
This can then be used to discover whether a prospective replacement will be suitable.

One mod at a time?
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PostPost by: rgh0 » Mon May 23, 2016 9:17 am

vincereynard wrote:
rgh0 wrote:
Yes you are correct with the calculations
cheers
Rohan


It had to happen sometime! :D

So before changing springs etc, the distance between the damper spring seats on the, fully extended, existing damper should be measured / established.
Which, presumably, should be the 8.6 > 9.0 inches mentioned in the workshop manual.
This can then be used to discover whether a prospective replacement will be suitable.

One mod at a time?


The 8.6 inches is the spring length at norrnal ride height, not at full suspension droop. You need to make sure the free length is greater than the full droop length to avoid the springs coming loose on full travel. This is not normally an issue with Elan or Plus 2 Front springs unless you have really hard full race setup.

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PostPost by: mariodschy » Mon May 23, 2016 9:30 am

vincereynard wrote:
According to the manual the front spring is 14.19 / 8.6 Free / fitted. A the initial poster stated.

So this would give a preload of 14.19 - 8.6 X 110 lbs = 559lbs.



This is not clear for me, 14,19 minus 8,6 should be 5,59 compressed length * 110lbs = 614,9lbs
So in my view the preload is 614,9 and not 559lbs.

Someone of us is wrong but Rohan has confirmed your post, seems that i've made the mistake but i couldn't find it please let me know where it is...

Mario
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PostPost by: rgh0 » Mon May 23, 2016 9:35 am

sorry I did not check the actual calculation :oops: - the formula is right :D

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PostPost by: vincereynard » Mon May 23, 2016 12:33 pm

vincereynard wrote:
rgh0 wrote:
Yes you are correct with the calculations
cheers
Rohan


It had to happen sometime! :D



I thought it was too good to be true. Mental multiplied by 100 instead of 110.

And I've just finished a biography of Isaac Newton. My apologies.
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PostPost by: mariodschy » Mon May 23, 2016 2:09 pm

vincereynard wrote:I thought it was too good to be true. Mental multiplied by 100 instead of 110.

Vince


Now it's clear where the 559 come from :)
- 1972 Lotus Elan Sprint LHD/DHC
- 1962 Austin Healey Sprite MK II - Sold 09.05.2016

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PostPost by: therolfie » Mon May 23, 2016 8:08 pm

Thanks for all the replies :)) I have fitted some old standard shocks with springs for now. Need the car for my wedding this weekend so priority is getting the interior done! Will be back in touch soon. Thanks again
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