Lotus Elan

fully adjustable rear control arm

PostPost by: wwpete » Fri May 19, 2017 8:06 pm

Does or has anyone made a completely adjustable rear arm? Adjustable for camber as well as toe? I am racing a +2 with street radial tires. with my other cars we needed to run a minimum 3 degrees and up to 5 degrees negative camber.
I also would like to hear from anyone who has used shock packers or different bump rubber to adjust body roll. I like the compliance of the suspension but body roll is too much. It might be that I need stiffer springs . The car has a full cage in it and weighs 2000 with gas and driver. 135 rear and 175 front springs.7/8 front bar.
Thanks
Bill
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PostPost by: rgh0 » Fri May 19, 2017 11:44 pm

Hi Bill

The rears adopt a fair amount of negative camber as they load up in a corner with the standard suspension geometry so additional static camber may not be needed beyond the around -1 degree you should have with a lowered suspension. It also will depend on the tires your using as some like more negative camber than others. There was discussion recently around adjustable to mounts for the strut to adjust camber. Most of the commercially available adjustable A frames are only adjustable for toe in and length cannot be adjust to increase camber but it is not hard to modify a standard frame.

I use spacers on the standard rear rubber springs on my Elan to bring them into play earlier which helps control rear roll and weight transfer. You can also get stiffer rear rubber springs but i found these to hard in my Elan but maybe would work in a heavier Plus 2.

Your spring rates are at the low end of what you would want in a track Elan and potentially to low for a heavier Plus 2. so going up in spring rate may be worth trying. The 7/8 roll bar may need to go up also depending on the final balance .

regards
Rohan
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PostPost by: wwpete » Sat May 20, 2017 6:29 pm

Thanks Rohan,
I have a lot of work to do on the car. We had our first race and found most of the weak parts of the car. I had pressed new rubber bushing in the rear wishbones and the outers were destroyed. Even tightened them down at ride height. I am think of trying Heim joints held in by delrin caps as a thrust surface. Since this is not vintage racing I have some options.
The car runs pretty low, around 3 inches so there is some gain of camber and the tire wear is pretty good. Tire temp was consistent across the tire but the pit road is so long that they cool fast.
Bill
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PostPost by: gav » Mon May 22, 2017 7:33 pm

Bill, Rohan

Not sure what the answer might be but with stiffer springs and front anti roll bar, would a light rear anti roll bar help?

Id be interested in thoughts

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Gavin
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PostPost by: wwpete » Tue May 23, 2017 4:22 am

Gavin,
I decided to try stiffer springs more like the little race Elan. 175 rear and 250 front. My corner weights are 450 front and 550 rear with driver and fuel. I carry about 18 gallons of gas which might explain the weight bias to the rear as well as a fair amount tubing to protect the cell. I have a limited amount of non stock parts I can add to the car so I am trying to avoid a sway bar.
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PostPost by: rgh0 » Tue May 23, 2017 9:48 am

I would try spacing down the rubber springs to bring the progressive spring rate at the rear into effect earlier first. If still not getting the handling balance you want then you could try a rear roll bar

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PostPost by: ecamiel » Tue May 23, 2017 1:22 pm

To set rear camber and take some rubber out of the system I made up some simple adjustable rear upper shock mounts with spherical bearings. The base is slotted athwartship for the 2 bolts so camber is adjustable. The bearing and housing are much smaller in diameter than the Locotone (?) mounts so there is plenty of room for adjustment.

I use a 1 inch front bar and an adjustable 3/8 rear bar, quick and easy trackside adjustments. Frankly, a 7/8 bar and varying corner weights would work just as well.

A hose clamp. not too tight, on the damper shaft will show you haw much travel you are actually using and where the rubber bump stop is engaging.
Personally, I differ with Rohan (rarely!) and avoid variable spring rates since they cause a change in balance in mid corner. The springs you are using should be hard enough so you need only short bump stops.
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PostPost by: rgh0 » Wed May 24, 2017 10:25 am

ecamiel wrote:To set rear camber and take some rubber out of the system I made up some simple adjustable rear upper shock mounts with spherical bearings. The base is slotted athwartship ....

Personally, I differ with Rohan (rarely!) and avoid variable spring rates since they cause a change in balance in mid corner. The springs you are using should be hard enough so you need only short bump stops.


athwartship --- now that's a term you don't often read on LotusElan.net :lol:

I personally dont find the variable rate rear spring upsetting but that is perhaps because they come into play early on initial turn in on my car before the rear end has really loaded up as the steel spring I use is relatively soft . But handling especially on the track is a very personal thing and you need to experiment

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Rohan
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