Suspension Design Issues - Specifically the rear suspension!
This information relates to the Spyder rear suspension system which provides the upper link.
The Problem
I installed the Spyder system when the chassis was rebuilt and ran it for three years. The problem was that I was never really satisfied with the handling of the car at the rear, and I had so little experience of the original Lotus design I had nothing to make a comparison with. It just felt wrong, so I was forever adjusting the rear wheel camber angles (the upper link allows for this), toe in etc. The car always felt twitchy and any steering change mid corner felt as though it would snap into oversteer. An Elite should be better than this.
It was Pat Thomas who finally confirmed what I had been thinking; the car suffers from roll-over oversteer, which explains why mid-corner changes were so unsettling.
If you look in the Lotus Workshop manual you will see a general layout diagram of the rear suspension. This may have been how the designer originally intended it to be as the drive shafts are parallel with the road, but production Elites are just not like this. Unless the car is heavily laden, or has sagging springs or a collapsing cross-member, the driveshafts will angle downwards. That's OK as they are still parallel with the lower link which means that the roll centre will be just above ground level. Now add in Spyders' upper link to the drawing and it is clear that as the link rises at the outboard end the roll centre rises and it goes way above ground level. (The front also has the roll centre just above ground level and should be a little lower than the rear for stability).
In my opinion this is the source of the problem: the pivot for the upper link, either inboard or outboard is in the wrong place!
The Proof
When you buy the Spyder system they take your original driveshafts and convert them to fit the new inboard CV joints by machining a spline onto the shaft. Thus, they are consumed by the conversion. Having reached my conclusion I bought a second hand set of driveshafts complete with alloy hubs ready to fit. It is easy to unbolt the Spyder system and fit the original design. Within 10 minutes of driving the car my confidence in its handling and roadholding ability at the rear just soared. Fantastic! All this time I had been missing out on the Elites legendary roadholding.
The Solution
Fundamentally I still believe that the upper link system is the way to go. It just needs to be redesigned so that the geometry exactly replicates the original design instead of corrupting it. There is also another downside and that is the Spyder fabricated steel upright. Each side (i.e. driveshaft, CV & adapter, Upright and upper link) weighs 7.5Kg more than the original design, which is a substantial penalty for unsprung weight. The only way round that is to find, or manufacture, an alloy upright, but overall the whole assembly will still weigh more.
I have not engineered this into the car yet but my solution is to move the inboard pivot point upwards. My plan is to make a new bracket that bolts into the place of the old pivot point and allows the upper link to be reattached so that it is parallel with the lower link.