rear suspension damping

[bengalcharlie]

Hi,

I experience the following when driving my plus two: The rear suspension is very soft and when driving in very long fast corners the rear hangs out considerably. I do not know if this is normal but I would prefer a slightly stiffer rear end. The springs are new and so are the koni shocks which are adjustable.
More of a worry is the fact if I load the car with wife and child and a full boot that the exhaust hits the road when driving through an undulation.
I would like your opinion how to solve this from happening.
I have heard that the koni shocks are adjustable but this is only for rebound and not compression so stiffening up the shocks would not solve my problem. Changing to stiffer springs and /or fitting a stabilizer bar would be an option???
Cheers
Robin

[MintSprint]

Be careful!!

Elans/Plus 2's do tend to feel a little soft and under-damped at the rear end.

Increasing roll resistance at one end of a car - either by fitting stiffer springs or by fitting an anti-roll bar (AKA sway bar, for our american cousins) increases weight transfer at that corner, which consequently decreases the grip.

In other words, increasing front roll resistance tends to increase understeer, whilst increasing rear roll resistance (as you are suggesting) tends to increase oversteer, which is not a good thing!

I'd suggest an expert second opinion to decide whether your car really does have a problem compared to standard.

Unless you have defective rear suspension, I'd suggest that you only increase the rear roll stiffness if you also increase the front stiffness in the same proportion, otherwise you run the risk of really messing up the handling balance.

[frearther]

Years ago, I fitted an rear bar to my S2 and very quickly found out about weight transfer! The car was almost unmanageable until I added a stiffer front bar. Since I was autocrossing at the time, I didn't worry about the hard ride. For a road car, I'd just leave it as it is, especially if, as Robin states, the +2 tends toward softness at the rear.

[ppnelan]

Later (?) +2s had aluminium packing pieces 'stuck' to the top of the damper tube/nut to make the bump stops come into operation earlier in the suspension travel. I have some but haven't fitted them yet - I am hoping they will avoid the bottoming-out problem with a 'car load'...

Matthew

[bengalcharlie]

thanks for the replies.
I might looking into making the rear suspension adjustable by fitting adjustable spring platforms so I could raise the whole rear end when traveling with the family. Anyone has done that on the plus two?
I agree that I prefer to leave the suspension standard to prevent upsetting the car. It handles very well so overall not unhappy with the roadholding. Might google some more to see what racers and hill climb people have done.

cheers
Robin

[MintSprint]

...I could raise the whole rear end when traveling with the family.

Again - be very careful!!

You can't seriously be suggesting that you'd raise the rear end every time you put the family in the back, then screw it down again when they step out and assuming there might be occasions when you drive the car one- or two-up with jacked up rear suspension, you run the risk of comedy oversteer.

In any case, the best way of employing your adjustable suspension is to use it to set the corner weights. Screwing it up and down all the time without benefit of corner weight scales will just throw the car's balance all over the place.

If you have a serious problem with grounding:
1) Check that the rear suspension is in proper working order and that the springs haven't relaxed, or that the dampers aren't faulty or set too soft.
2) Consider stiffening the whole car up, with proportionate increase in stiffness front and rear.

Anything done to raise/stiffen the rear end in isolation will lead to an increase in oversteer.

You'll find that competition cars run much stiffer springs all round, usually with adjustable anti-roll bars front and rear, but the ratios of front to rear stiffness won't differ all that much from a standard car.

[jono]

Hi,

Slight thread hijack (apologies ) but might the Spyder double wishbone and spring damper rear set up be the answer to your problems?

I have been thinking of going down this route myself in my Plus 2 rebuild and ditching the Chapman struts but don't really know what real world difference it will make - has anyone used this set up on here and can they relay their experiences?

jono

[MintSprint]

Slight thread hijack (apologies ) but might the Spyder double wishbone and spring damper rear set up be the answer to your problems?

Not in itself, no.

Apologies to any suspension experts for gross over-simplification, but:

The problem of bottoming under heavy loads is down to spring rate - ie the amount the springs compress for a given load upon them, which is not significantly related to the linkage geometry.

The problem of oversteer/understeer balance is down (mainly) to the balance of front/rear roll stiffness (again spring-rate, rather than geometry related).

The differing camber and roll centre behaviour between Spyder wishbones and Chapman strut may make a difference in allowing you to run stiffer springs at the rear without upsetting the balance so much, but not a huge one... you'd probably still end up having to increase spring rates all round to cure the 'bottoming' problem.

...and, of course, fitting Spyder double wishbones is not only expensive in itself, it also requires that the car is fitted with a Spyder spaceframe replacement chassis; rather an expensive solution if your car has a pressed steel chassis at the moment.

Much cheaper and simpler to just increase the spring rates all round (in proportion front and rear).

[jono]

..ah yes, good point Mintsprint!

Mine is already on a Sypder spaceframe and I forgot that the majority might not be.

Still be interested to learn of anyone's experience with this upgrade though. Yes it is fairly expensive but it looks a lot better located than the chapman strut arrangement and does away with the lotocone arrangement too, big reduction in unsprung weight as well I would think.

Back on topic though, re-connecting the rear ARB on my Seven certainly made it much more oversteery than with it disconnected, which was errrm nice

[rgh0]

My plus 2s 130/5 came with those same aluminium spacers in a box of spare bits and not fitted to the car. I never recognised them for what they are over the last 30 years until mentioned now by Matthew.

The original Aeon rubber springs come in different ratings and you may consider fitting a stiffer or longer rubber spring see the manufacturers website - http://www.timbren.com/aeon-rubber-springs.htm.

If bottoming out is a signficant problem then a combination of spacers, stiffer aeon springs, adjustable spring platsforms and / or slightly longer / stiffer rear springs will solve the problem

I have used 20 mm spacers under the aeon rubber springs on my competition elan for many years as it improves the handling on the limit by restricting rear squat in hard cornering so I would not be concerned at adding the spacers to the plus 2 to limit grounding on bumps with full load. Lotus were obviously happy with this solution if they used it on the later plus 2's also - and they knew what they were doing when it came to handling.

cheers
Rohan

[bengalcharlie]

thank you for your advice Rohan,

I am a little confused though by the website you refered to. It looks to me as a bump stop that fits over the shock rod? Is that correct?
If so I am sure I have one fitted. It is hard to explain but as mentioned in my previous post I do find that the suspension is rather soft in very long fast corners ( between 100-120km/hr) and I am sure that a stiffer spring and or firmer shock would be a improvement. Would you know what the spring rate is for the rear shocks standard?
I have new springs fitted but also have my old springs so I could have these tested to find out. I am not looking forward to take apart the rear end again. Last time I had no skin left on both my index fingers trying to pull the shock rods through the top mountings till finally after a hour of failed efforts I centered the shocks shafts with a tiny little scredriver and I managed to pull them straight through. Sometimes you learn the hard way!
In the mean time I will fit a hose clamp back on the exhaust pipe to rear silencer because that way I have just enough clearance for the exhaust clamp not to hit the road.
Cheers
Robin

[rgh0]

Hi Robin

Standard plus 2 rear spring rate is 93 lb / inch. Standard spring is 9.7 working coils of 11mm diameter wire. freelength 16.0 inches fitted length at normal ride height 8.6 inches.

Yes the Aeon rubber springs fit over the shock rod. If you have those orginial springs fitted and not replaced with small bump stops and they are in good condition then adding a spacer of about 20 to 30 mm thickness will bring the rubber springs into play earlier that will help stop grounding and inprove handling.

cheers
Rohan

[bengalcharlie]

Thanks again Roahn for the spring specs. I will definetly check these out find out what is fitted to my car and I think that your solution of fitting a spacer will solve my problem.
Cheers
Robin

[bengalcharlie]

Hi guys,

Just to let you know that I have solved my problem by fitting two spring spacers bought for 6 US from autozone in the US, whilst visiting my lotus elite friend last week. After discussing the problem with him he suggested we should try it and I am happy with the result. Before fitting these spacers the car was slightly lower at the rear and now the measurements front and rear are equal. I was afraid for noticable increase in oversteer as many of you warned me for, but the handling is the same or even better.
So for now I leave it as it is because I can not see a good reason to spend serious money and time on adjustable suspension perches etc..
Cheers
Robin

[gordonlund]

Quite a few years ago I replaced my rear springs for new ones, only to find that the rear end was quite close to the road when laden and scraped the exhaust at the slightest provacation. The springs looked identical, same number of coils same free length, mean diameter, and wire diameter looked the same. But being an engineer I took my trusty micrometer to the spring wire and found it was down in size by 0.020inches. That made all the differance!!

Spring rate is proportional to wire diameter to the fourth power. Changing the springs to OE spec made all the differance. By the way the original springs were slightly larger in wire diameter and hence were quite stiff. I parted with them at an autojumble just after I got the new ones. Wish I had kept them even though they were a bit rusty.

Gordon