Lotus Elan

Plus 2 rear anti roll (sway) bar

PostPost by: JonB » Tue Apr 30, 2019 8:19 am

Quick question - has anyone fitted a rear anti roll bar to a Plus 2, and if so, how?

Are there any threads on here that describe it? I had a look but couldn't find anything (yet).
Late 1972 Elan Plus 2S 130/5 - UK - Unit 50/1115L
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PostPost by: jono » Tue Apr 30, 2019 8:49 am

No, but I seem to recall that Spyder do a kit.

But why would you want to do that as increasing roll resistance at the rear will surely increase the tendency to oversteer?

If you like that then great, but it's not for me on a road car :D
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PostPost by: JonB » Tue Apr 30, 2019 10:55 am

Will it? Didn't know that.. just trying to reduce the amount of roll somehow. Have a front roll bar of course, but still it feels like it is rolling too much. Maybe I need a second opinion.

Thanks muchly!
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PostPost by: jono » Tue Apr 30, 2019 12:33 pm

Yeah, you will dramatically increase oversteer with the addition of a rear ARB, all else being equal.

I had a Caterham where the rear ARB was ajustable for stiffness and the one notch made a huge difference.

I've played round with the rear spring and damper rates on my Plus two for ages (as I'm a 'fiddler') and eventually settled on 120lb narrow springs and a 65mm softish poly bump stop but without the alloy spacers (as these induced a sudden stiffening effect and oversteer tendency which was quite disconcerting). This is with AVO adjustable dampers.

This set up works very well to me and firms up the rear reducing roll and more suits my style of driving - with TTR front spring dampers the car handles very well at little cost to compliance. It much more confidence inspiring.

That said, had I started with a very original car I think I would have kept it all original but mine was a basket case at the outset which I decided to 'improve' in a number of areas and I never intended a purist restoration
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PostPost by: Davidb » Tue Apr 30, 2019 3:55 pm

I would suggest looking at the way the rear bar is fitted to the 26R and adapt that-but make it adjustable would be my suggestion.
Will you benefit from a rear bar? It depends how you drive and under what conditions. I have been running a rear bar on my Elan for the past two years-with a stock front bar-the experts will tell you this is a no-no. However, I drive in long events, in bad weather, with a co-driver, baggage and tools and spares-a lot of weight over the rear and the rear bar works. For the latest event I fitted a 13/16th front bar and that was an improvement too. Jackie Stewart knew what he was doing in 1964.
This is on an Elan +1 of course.
'65 S2 4844
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PostPost by: rgh0 » Wed May 01, 2019 11:27 am

Col at Elan Trikbits has an ebook on the design for an adjustable rear bar. The design is a nice elegant solution that he has built and works on his Elan and could be installed the same on a Plus 2.

Personally I have never seen the need for a rear bar in either my Elan on the track or my plus 2 on the road if the rest of the suspension is setup right. The rear Aeon rubber springs are critical to this setup.

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PostPost by: JonB » Wed May 01, 2019 11:58 am

Hi Rohan

I used a boroscope to check that my car has Aeons fitted to the rear - the pictures are here: viewtopic.php?f=42&t=41214&start=285

Do they suffer from noticeable age related degeneration? Maybe go soft after 40 years?
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PostPost by: rgh0 » Wed May 01, 2019 12:23 pm

Hard to tell from the photos. The shape does not look like the original Aeons and if they are, they have deteriorated as the gap between the rubber and the shock rock is larger than it should be.

Before investing in a rear bar i would fit new aeons and the equivalent of the spacers that Lotus added on the latter Plus 2 and see what that does to handling. With the latter Plus 2 standard setup in good condition I find my Plus 2 handling as a road car close to perfect though it does roll to much if I use the plus 2 on the track.

If tracking the Plus 2 I would stiffen the front and rear springs around 50% above standard rate and go to a bigger front bar at around 7/8 inch / 22 mm and drop the suspension ride height a little to get a little more negative camber front and rear and bring in the rear Aeons earlier in a corner.

If still not satisfied with the handling I then may look at a rear bar.

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PostPost by: JonB » Wed May 01, 2019 2:27 pm

OK Rohan, thanks for the wise words.

I have already acquired a set of good use Konis for the rear (as it already has Konis) so I will be taking the back end apart at some point. I'll see what the condition is of the Aeons at that point. Regarding modern replacements, are they any good? I'd read on another thread that they were hard to get.
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PostPost by: RichardHawkins » Wed May 01, 2019 9:33 pm

John,

A few months back this subject came up with my local Lotus friends, one of which had a pair of original AEON rubber buffers, which looked fine. The idea was to measure the spring rate and compare with those currently available.

As soon as the old AEON's were loaded it became obvious they were severely worn. Cracks that were not apparent in the static condition became obvious, and the two original AEON's required vastly different loads for the same deflection.

In conclusion we decided that 45 year old AEON's could not be trusted and that we were unable to decide if those currently available were of the correct spring rate.

Hope this helps,

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PostPost by: JonB » Thu May 02, 2019 6:56 am

Blimey. If mine are tatered it would certainly explain a thing or two!

And, double blimey - how's a fellow supposed to know what to replace them with?
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