Trailing Arms needed?

[bitsilly]

Does anyone know if the trailing arms are needed on a Ram?

I recall a conversation with I think Russel, and he pointed out the incompatibility of the arc of the arms, and the linear motion of the suspension, but I was wondering if anyone had removed them and felt a difference? Do they do anything? Are they needed?

Cheers

[Simon R]

Does anyone know if the trailing arms are needed on a Ram?

I recall a conversation with I think Russel, and he pointed out the incompatibility of the arc of the arms, and the linear motion of the suspension, but I was wondering if anyone had removed them and felt a difference? Do they do anything? Are they needed?

Cheers

At the risk of starting world war III (again), the trailing arms were only there to locate the jag axle cage which floated around in its rubber bush mountings to the body. These bushes allowed some compliance to avoid the suspension binding up.

Standard jag axle don't need 'em...... might be different if you've had 'em shortened and the welding/sleeving is questionable.

I would not however condone removing something your kit manufacturer has designed in.

Cheers,

Simon

[mylesdw]

I remember discussing this with Adrian Cocking and the summary answer is that they put them in because people were happier to see them there.

They don't do anything except cause binding in the IRS and earlier wear in the lower control are bearings.

This conversation occurred quite late in my build and I did not want to cut all the brackets off at that point and I was worried that the MOT tester would notice the obviously missing arms so I fitted them but drilled some holes through the rubbers to make them very soft (ineffectual) in tension and compression.

[bitsilly]

That is a good idea.
I left them on for SVA initially, hadn't thought about MOT's.

Cheers gents

[craggle]

Personally I like trailing arms and I think they do take some flex out of the wishbones under acceleration and braking. Unfortunately they do nothing for the rotational forces seen in the wishbone which are far greater than any backwards or forwards motion but that's why they used a single tube for that job.

It is kind of surprising that Ram fitted them. I'm sure they were intelligent enough to realise that they wouldn't really work properly because of the way the suspension moves.

Question is though, How much does the suspension travel in normal use and how much of an arc does the trailing arm make as it moves.
My guess on both counts is not very much. If the trailing arm also has rubber bushes then the amount of load it will place on the wishbone will be minimal.

If anyone can measure the amount of travel on the suspension and the length of the trailing arm, I'll work out what the displacement is but to be honest, If you have them fitted, I'd leave them there with soft rubber bushes in the arm. Don't be tempted to fit polyurethane replacements.

One other thing I saw once was a triangulated lower wishbone with bars welded between the end of the wishbone and the cast inner pivot. A complete waste of time with absolutely no strength to it!

Just as a matter of interest, the only company I know that got these right was Dax on their standard chassis. They fit a trailing arm to the wishbone but it is angled inwards at about 45° and the inner pivot point on the chassis is placed in line with the lower wishbone pivot shaft. The fixing on the outer end of the wishbone is a solid, steel fixing. no bushes needed as the trailing arm dosen't move in relation to the wishbone as the suspension travels up and down.

Craig.

[mylesdw]

If you estimate that the arm is 150mm long and the suspension travel is + and - 50mm then then the arm attempts to pull the lower 'wishbone' out of line by 8mm at full travel and by 2mm at 25mm travel. That is a lot. If the arm is 200mm long then the figures reduce to 6mm and 1.5mm which is still significant.

[craggle]

I was under the impression the arms are at least 300mm and more like 400mm long.
Are they really that short. If so, then yes, the amount of pull on the arm through the arc of movement is significant.

Craig.

[mylesdw]

Found a picture, you are right, they are more like 300mm long but that still makes the figures 4mm and 1mm respectively.

[Antony]

If you estimate that the arm is 150mm long and the suspension travel is + and - 50mm then then the arm attempts to pull the lower 'wishbone' out of line by 8mm at full travel and by 2mm at 25mm travel. That is a lot. If the arm is 200mm long then the figures reduce to 6mm and 1.5mm which is still significant.

I agree with the travel and change of length for the radius arm over 2"
With my first Almac cobra the E type IRS we tried using the Jaguar arm with large compliant bush, and the wheel had considerable fore/aft movement, so went back to the poly bush on one end and rod end on the other this obviously restricts free movement of the IRS.

For serious racing on sticky rubber I would not use a std Jaguar IRS without a radius arm and would consider some serious improvements as cobras can be wishy washy on high speed corners with the std Jaguar IRS. Some Cobras the radius arm forward location point is on the same axis line as the Jag inner bushes so that works alright if you can fit to your car. Another kit here had Jaguar but with top and bottom wishbones and sliding spline axles a nice bit of clever engineering. I have seen a top arm attached to the large alloy hub carriers by bolting on top, but that still doesnt solve the load on the lower arm inner bushes to my way of thinking!

[craggle]

Hi Antony

Just thought I'd chuck a picture in of the Dax setup on my car. The black arm (Trailing or radius?) is firmly attached at the outboard end and pivots on the same axis as the inner pivot point on a rod end attached to the chassis.

I like the idea of a top and bottom wishbone setup. Think I too have seen that somewhere before but sure the upper mounts were welded to the alloy hub.

Craig.