Lomax 223 anti roll bar

[Davidm]

Rocketman
Most Pembletons have uprated springs and this is recommended in the build manual. (My car is unusual in having standard 2cv springs and an ARB and I am happy with the handling).
You could explore the effect of stiffer springs by inserting blocks between coils before forking out to replace the springs or manufactured upraters like those offered by Graysons.
Uprated springs will have a greater outside diameter or smaller inside diameter than standard springs so would they fit your Lomax ?
Davidm

[namster]

I made up my own ARB for my last pembleton using a length of 5/8ths EN8 bar.

The good thing about steel is that regardless of type they all have pretty much the same youngs modulus so unless you're going anywhere near the yeild then you don't need anything particularly fancy

It was probably a bit stiff as it introduced some understeer, but body roll was greatly reduced. I think I'd either shorten the length of the lever or drop diameter if I was doing the same again. I welded on some ends to the bar and some threaded bosses onto the arms. I used MG Midget bushes and brackets to mount to the chassis and male/female rod ends for drop links. (I did plan on using BMW drop links pictured ones but couldn't make the angles work)

20200924_215327_copy_1512x2016.jpg (930.51 KiB) Viewed 43372 times

20210418_200249_copy_2016x1512.jpg (606.73 KiB) Viewed 43372 times

[2cvman]

up.png (110.9 KiB) Viewed 43369 times

[cmwbob]

Is the RH rear dummy arm in situ ? If not the spring canister is just freewheeling that side. Ideally the rear dummy arm should be interlinked to the rear wheel, as a minimum the dummy arm should be in place and the rear spring pre-tensioned via adjusting the tie rod.

The lack of front ARB may then be less problematic unless you like your chicanes, then the ARB is near essential

[Rocketman1955]

Thanks for the suggestions. I have been trying to think of ways to prove what is going on.
Unfortunately the 2 CV coil springs are in the suspension cylinder cans and it is not trivial to fit coil overs.
Re-modelling the anti-roll bar is possible, but improving the inherent stability of the suspension would preferred.
Regards the suspension linkages, the active rear arm is on the RHS. The front LHS cylinder tie rod is only connected the front arm. The LHS rear tie rod is not connected (no dummy arm).

In a non-roll situation, the RHS of the car is supported by front and rear springs.
On the LHS only the front spring supports the car (1) and the cylinder is fully forward on the compressed buffer. Statically the car is level.

To try and compare front springs, the car was jacked up centrally at the rear until the rear wheel was off the ground. ie low input from the rear spring on the active side.
Then most of the cars weight should be shared by the front springs.
As expected (?) the LHS front ride height increased ~45mm, vs the RHS~15mm – the difference being due to higher preload on the LHS. (see 1 above)
However, more important than load is stiffness rate. (Tie rods lengths were not adjusted.)
This was checked by measuring the drop in body height at the windscreen fixing when I sat in the passenger and drivers seats. The LHS drop was ~5mm vs RHS ~ 15mm, indicating the LHS is stiffer and not softer as expected!
Maybe the front springs are non-linear and stiffer when compressed more?

Will investigate more, but anti-roll bar might be the way to go as car performed well before I had to remove it!

[Davidm]

There are several variables involved here !
Another possibility for confusion could be differences in the front springs between left and right. The Pembleton uses exposed springs so the spring canisters from the donor are discarded (or sold). I found significant differences in spring lengths and one spring was broken near the end so they all had different spring rates !
I assume it's too big a job to swap canisters L to R to see if that changes things ?
Davidm

[Rocketman1955]

Swopping cylinders is on the list of potential checks! Not particularly difficult.
Also swopping dampers and pretensioning the LH cylinder rear spring.
Need to find time to blitz all the options and try to make sense of the results.

[cmwbob]

If as you say, there is no dummy rear arm then first step is to refit the rear spring tension rod and create a substitute anchor point on chassis.

Ensure there is adjustment and then play with the free-standing pre-tensioning of the rear spring.

[Rocketman1955]

Have now tensioned the rear spring on the redundant side using the original tie rod end fitting and knife edge in a strap secured to the rear of the chassis.
The thread exposures in the tie rods are similar to those on the side with the active rear arm.
The rear spring is definitely loaded as the front and rear buffers now look their normal shape. Previously there was no load on the rear buffer and the front buffer was heavily compressed by the cylinder against the stop as the front spring only was used to get the front ride height.
Regards body roll it has made no noticeable difference & may be slightly worse.

Looking at the suspension design, I believe the 2 springs in the cylinder are acting in series.
Given the 2 springs are similar stiffnesses, then for a given load there will be 2x the compression of a single spring.
So roll will not be reduced.

However, roll turning left and loading the active side of the car is far less, yet both springs are active on that side and the rear wheel contributes very little to resist roll!

[namster]

This video is a good description of how the 2cv suspension works.

https://youtu.be/j7pFxgDmZXQ?si=szoN0nvYLGzlbvsu

Simply putting one of the rears under tension will really muck up you're front spring rates. The two arms are linked to provide equal raise on the front when you hit a rear bump, or vice verse.

Bob has mentioned a few times in this thread that the bar between the rear arms is to equally link front/rear suspension. With only one side linked (whilst retaining floating canisters) you'll like get an odd feel.

The front/rear linked suspension could be "deleted" by fixing the canisters (IE, remove the possibility of the canisters to float) and this would resolve your issue.

On a three wheeler the only thing that controls body roll is the front axle. In this instance the front axle is being affected by the travel of the rear, but without the linked rear arms, the rear suspension load is only affecting one side of the front axle, thus giving different feel in left and right turns.