Lotus Elan

Further question about rear springs on Sprint

PostPost by: TroonSprint » Tue Dec 09, 2014 8:21 pm

Some of you will have seen my recent thread about suspension issues on the rebuild of my Sprint FHC, and thanks to Rohan I am happy with the front now. At the rear I have adjustable perches for 2.25" ID springs. I want to retain close to the original spring rate which according to the manual was 67.5 lb in. If I buy some 75 lb in springs like these https://www.merlinmotorsport.co.uk/s/suspension-steering/coilover-springs/faulkners-race-springs/2-25-inch-i-d-coilover-springs, what free length should I go for?

Thanks in anticipation of your wisdom,
Mike
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PostPost by: rgh0 » Wed Dec 10, 2014 9:42 am

Standard rear spring installed length at normal ride height is 8 inches. Normal spring load at this length is 450 lbs. i.e. 14.71 free length to 8.0 fitted length at 67.5 lbs /in standard spring rate- (This is data from the manual).

So a 75 lbs/in rear spring for an 8.0 inch installed length needs to be 14 inch free length assuming your adjustable platform is set at the same location of the normal fixed platform

cheers
Rohan
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PostPost by: ianf » Sat Feb 14, 2015 8:47 pm

I know this is a bit late but I thought the same about spring rates and fitted 75lb 2.25" rears. OK if car lightly laden but became coil bound with two up and a case or two. Also crashed badly on poor surfaces (a bit like hitting a bump stop). Fitted 100lb springs and the rear is perfect, the front is now occasionally crashing so I will put in 120s there (as Rohan's advice elsewhere).

Cheers,

Ian
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PostPost by: rgh0 » Sat Feb 14, 2015 9:58 pm

Hi Ian

Yes when modifying springs you always need to check the full bump situation for spring bind to ensure the suspension comes onto its bump stops correctly and full droop for the springs remaining seated properly and not coming loose.

cheers
Rohan
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