Lotus Elan

2.5" rear spring specifications

PostPost by: steve71 » Tue Jan 03, 2006 9:44 am

Hello all,

I am about to fit adjustable spring perches and 2.5" ID springs to the rear of my sprint. Can anyone suggest the dimensions of springs I would need to fit for normal spirited road use?

Thanks,
Steve.
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PostPost by: Dag-Henning » Tue Jan 03, 2006 11:50 am

Steve, - do not change the rates of your rear springs, without also changing the front ones. If you use std. rate rears in 2 1/2", I would guess 12" length would be a good start.

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PostPost by: steve71 » Wed Jan 04, 2006 2:24 am

Thanks Dag. My front springs are standard rate so I will keep the rear standard rate also.

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PostPost by: rgh0 » Wed Jan 04, 2006 9:48 am

Steve

If you dont have a copy of the Dave Bean catalogue you should get one. The catalogue gives a range of settings from standard to full race and I have found them all good for the relevant applications.

For fast road use they recommend an increase in stiffness of about 50% versus standard which is about the smallest increment most drivers can actually feel.

DB fast raod specs:
115 lb/in and 12 to 13.5 inch free length front depending on shocks used
95 lb/in and 12 inch free length rear
.750 inch roll bar

For road use this setting is probably even more relevant today than when DB first made the recommendation in his catalogue about 20 years ago (it has not change in that time despite the available tyres getting a lot stickier). Today I would use DB recommendations for fast road springs but increase the front roll bar to 13/16 or 7/8 diameter.

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PostPost by: type26owner » Wed Jan 04, 2006 2:39 pm

Been waiting for Rohan to speak up. Concur with everything he says cause it's the exact setup on my Elan. Went with the Stage 2 DBE springs, 13/16" swaybar and Rohan's modifications to Chapman Struts. This requires you to remain at the stock ride height but will reduce the body roll when cornering at the limit by about half. You'll still have to choose wisely the tires or you can render the handling back to lousy with a tall, skinny econo-box tire.

The only other change one should consider to do is to replace the front upper a-arms to adjustable ones and lean the front wheels in from slightly positive camber to about 2 degrees negative. That's a $600 investment and would take a long time like 10+ years of daily driving for one to recover that expense by reducing the front tire outside edge wear rate appreciably.
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PostPost by: steve71 » Thu Jan 05, 2006 12:03 am

Thanks Gents. I have just registered at the Elanmods website and will look at your strut modifications Rohan.

I have spent the last 20 or so years setting up and riding motorcycles and the Elan is a whole new ballgame for me.

At the moment I am getting alot of understeer in my car. From reading on the forums I belive that the new CV drive shafts and old rear springs may be major contributing factors.

Are there some basic do's and don'ts I should keep in mind when setting up the car to help keep it balanced? Could you recommend any books which would help shed some light on setting up the Elan and understanding what is going on with all those wheels :lol:

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PostPost by: rgh0 » Thu Jan 05, 2006 7:33 am

Steve

In terms of books the Carroll Smith series are a good investment

Tune to Win
Drive to Win
Prepare to Win
Engineer to Win

While focused on open wheel race cars everything he says is good practical and well proven knowledge that is equally applicable to setting up a reliable and good handling Elan and driving it well.

My rear strut mod is to use to plastic spacers around 15 to 20 mm thick and 50mm diameter above and below the strut bump rubber. This brings the bump rubber into play earlier and stops the car squatting on its outside rear wheel so much and lifting the inside front high in the air.

I just went to a local suspension shop and looked through their plastic bushings until I fouind something with the right ID, OD and thickness to get the spacers. I think it was a 70's Torana front supension bush IIRC. I am in Melbourne so if you want to talk more give me a call on 0417 668 650.

Rohan




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PostPost by: type26owner » Thu Jan 05, 2006 5:46 pm

I would recommend you read Competition Driving by Alain Prost. It's been out of print for years but can still be found as a used copy. After that go through a driving school. It's no fun to bounce off a wall while coming up to speed.

Once you've gotten the feel of a good handling car for a baseline only then can you recognize whether or not your Elan is behaving correctly.

For setup stuff there's Fred Puhn's book and the DBE catalog.
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PostPost by: steve71 » Fri Jan 06, 2006 11:29 pm

Thanks for the advice Gents. I think a driving course sounds like a very good idea.

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PostPost by: mark030358 » Sun Jan 08, 2006 12:16 am

Gents,
How do you modify the chapman strut for 2.5" springs? Does this involve fitting new tubes?

cheers
Mark
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PostPost by: steve71 » Sun Jan 08, 2006 5:37 am

Mark

You use adjustable spring perches, these are a piece of threaded tube which slides over the existing strut tube (after original seat has been removed) and is fitted with a threaded spring seat and lockring. There is also a modified top cap to suit the smaller spring. Paul Matty lists them for 2 1/4" springs and there is a small picture of one on page 24 of the catalouge.

Here in Australia I have sourced the perches from a 4WD suspension shop and will modify the top caps myself.

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PostPost by: steveww » Sun Jan 08, 2006 7:27 pm

I am in the middle of doing this at the moment. I got the 2.25" kit from TTR. Once you have removed the strut you need to grind off the old spring seat, then the new threaded tube slides over and is welded in place. Quite an engineering job but nothing a well equipped DIYer can not do.
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PostPost by: type36lotus » Sun Jan 08, 2006 8:29 pm

steveww wrote:...you need to grind off the old spring seat...
Simply said, but time consuming. I recently did mine, took all day of grinding to do both sides. But as Steve says "...but nothing a well equipped DIYer can not do." There is not a lot of welding required, so anyone with a MIG or gas kit could do it.
Mike Geiger
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PostPost by: Old English White » Sun Jan 08, 2006 8:45 pm

... I have this done last year ... see picture on my gallery!
A good opportunity to check everything (bearing , brackes ...)
My mechanic add a hole and a screw to complete with oil or coolant in the tube with the coil ...
I am very proud of his work ... Merci Ange ! :wink:
With all new bushes , it will transform your car.
Christian.
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PostPost by: type26owner » Mon Jan 09, 2006 12:51 am

The kit Dave Bean sells works differently. The new threaded sleeve is aluminum and it gets epoxied into place. The existing steel collar that is the lower spring platform is not cut completely off. Just the portion that flares out away from the housing. The bit which is brazed or spotwelded to the housing is still required so the force of the spring has a way to be transmitted onto the housing. It's a slick design. The spring ID is 2.5" versus the others which is only 2.25". With the smaller 2.25" springs the threaded piece must be very fine threads, is this correct? The 2.5" unit has coarse acme thread which is something like 8tpi.
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