Lotus Elan

Plus 2 rear suspension - again!

PostPost by: jono » Fri Oct 07, 2016 8:39 am

Apologies now for this fairly long post but please bear with me (and I know this has almost been done to death)

I am happy with the way my Plus 2 handles expect for the rear suspension under 'hardish' cornering. Currently I have TTR fast road spring dampers on the front and a standard ARB - all works very nicely at the front.

On the rear I converted to narrow springs and adjustable perches. I have Koni classic dampers in good condition set just under maximum and they feel about right though rebound appears quite slow. I have played with springs for a while and currently have fitted 120lb 14 inch Faulkner springs and again they seem to be okay and, interestingly, are what TTR recommend on a fast road type set up.

I have recently reverted back to metalastic suspension bushes and installed new Lotocones

Bump stops and spacers are another story - I've used Powerflex 65mm progressive stop with the Lotus alloy spacers and am now onto Kelvedon bump stops without the spacers - the Kelvedon stops are like an ice cream cone and are about 5 inches long - I've left then long from the moment though they are intended to be cut to length to suit each application.

The problem I've always had, and still have, is that when the suspension comes into play with the bump stop it ramps up very quickly ie it suddenly turns from nice progression to firm and this is quite unsettling as it feels like the rear is about to snap away (almost feels rear 'steery'). This seems worse on left hand corners but perhaps that's because there's 14 stones of me on the loaded side of the car?

Speaking with TTR recently about brake pads they reckoned that their special Koni dampers would transform the car but I can't understand why as the issue appears to be the bumps stops - any thoughts?

I'm also a little concerned about the limited travel nature of these Koni special inserts and what happens when they reach their maximum extension (going light over a crest, outside wheel under hard cornering etc)

I am now thinking, having tried all else that perhaps I just need to remove the bumps stops altogether and rely just on the uprated springs (perhaps with a very small bump stop to act just as that in the case of a 'bottom out' situation).

I feel that the car is 90% of the way to handling beautifully but I can't find that last bit of the puzzle. Chapman would be cursing me for messing!

Of course some will ask why I didn't just leave it as standard which is a very fair point - but that would defeat the whole purpose of owning a Lotus which we all know is a tinkerers delight :D

Comments, advice and experiences much appreciated.

Jon
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PostPost by: rgh0 » Fri Oct 07, 2016 11:25 am

You most of the way there I think. What is the spring rate of your front springs they need to be in the 150 to 180 lb/in range to match the rears.

Limited droop with stiffer rear suspension is not a problem as the spring load and thus tyre load close to zero when it reaches full droop.

The suspension should smoothly load up onto the rubber springs at the rear as you corner hard. Without the rubber springs you will suffer a sudden roll oversteer as you corner hard which is difficult to manage. If you feel a sudden transition as you rol onto the rubber springs then they are to stiff

A stiffer front bar may help also

cheers
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PostPost by: jono » Fri Oct 07, 2016 3:08 pm

Many thanks Rohan,

The front units are TTR's fast road spring dampers and are designed for use with their rear Koni specials and the 120lb springs I have fitted so, at least in theory, they are a good match

What you say below described exactly the effect I am experiencing. Having tried 2 types of bump stops without success, what do you think about my suggestion of removing them completely and relying on the up rated springs?

Cheers

Jon
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PostPost by: rgh0 » Fri Oct 07, 2016 9:45 pm

its worth a try you can always replace them if its worse.

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