Outer Limits 4x4 Board

I was trolling around on a british forum and saw these. Very nice. I'm not sure they'd work as well for a patrol though with the large bend in the arms over the tie rod.

can u post a link to where u found them, they look interesting

I have some mates that are on http://www.devon4x4.com

They mostly do the landrover rangie thing but they have some really cool tricks that can be used on anything. Their forum is down at the moment but it'll be back up before too long.

thanks, its giving me ball rash trying to work out which way to swing. Will check the site out.

Cheers, Dan

Be aware that the part of a radius arm between the pair of axle mounts can be subjected to high bending loads and tube has very poor section properties for resisting bending (low sectional modulus, Z value in engineering calcs & tables of section properties).

What benefit can that construction offer to sacrifice on road safety?

I don't think I'm being too conservative by being alarmed by those arms if they are used on the road.

Bush65 wrote:Be aware that the part of a radius arm between the pair of axle mounts can be subjected to high bending loads and tube has very poor section properties for resisting bending (low sectional modulus, Z value in engineering calcs & tables of section properties).

What benefit can that construction offer to sacrifice on road safety?

I don't think I'm being too conservative by being alarmed by those arms if they are used on the road.

I guess in some part tit depends on the materails they are made from .. if it is all chromo and heat treated afterward (using the absloute limit of my engineering knowledge) I could see how they would work..

Bush65 wrote:Be aware that the part of a radius arm between the pair of axle mounts can be subjected to high bending loads and tube has very poor section properties for resisting bending (low sectional modulus, Z value in engineering calcs & tables of section properties).

What benefit can that construction offer to sacrifice on road safety?

I don't think I'm being too conservative by being alarmed by those arms if they are used on the road.

Yeah that is why I mentioned that I wouldn't like to try them on a patrol with the large bends and the large separation in the diff mounts compared to other cars like the landrover and landloser. As you can see by the chassis mount joints these are not for a road going car.

sorta looks like a fancy ladder or wrap bar for a leaf sprung vehicle,hence the joints sitting along side?

They're definately radius arms. I'd leave a link to the thread but the forum is still down at the moment. Made by north industries over in the UK. They do some really nice work.

Bush65 wrote:Be aware that the part of a radius arm between the pair of axle mounts can be subjected to high bending loads and tube has very poor section properties for resisting bending (low sectional modulus, Z value in engineering calcs & tables of section properties).

What benefit can that construction offer to sacrifice on road safety?

I don't think I'm being too conservative by being alarmed by those arms if they are used on the road.

I was thinking that that point was suspect.

I'm not sure that you'd want to resist bending.

Standard radius arms allow some torsional flex through that part of the arm, ie, between the 2 axle end bushs.
The material used in those arms will resist that flex which may cause issues.

steel wrote:I'm not sure that you'd want to resist bending.

Standard radius arms allow some torsional flex through that part of the arm, ie, between the 2 axle end bushs.
The material used in those arms will resist that flex which may cause issues.

regarding bending, it takes 2300psi with a 5 inch cylinder ram to bend a stock LR RA at the rear axle end bush. Only 1800psi approx 150mm rear of this point. So I wouldnt think that the "cup" would bend in normal use...

Are you saying the arm twists within itself?

Serg

From looking just at the pics I would have thought that the biggest risk point for bending would be just behind the rear axle mount. There is extra bracing in the cup area and I wouldn't think there would be much force in that area compared to the longer part of the arm.

uninformed wrote:
Are you saying the arm twists within itself?

Serg

Yeah sort of, it will flex torsionally along it's length (like a torsion bar), but just between the 2 axle end bushs, or the "cup" area as some call it.

toughnut wrote:From looking just at the pics I would have thought that the biggest risk point for bending would be just behind the rear axle mount. There is extra bracing in the cup area and I wouldn't think there would be much force in that area compared to the longer part of the arm.

There are large forces in the "cup" area, once the bushs bind under the affects of suspension articulation, the forces are transferred through to the arms, which flex a small amount.

Bush65 wrote:Be aware that the part of a radius arm between the pair of axle mounts can be subjected to high bending loads and tube has very poor section properties for resisting bending (low sectional modulus, Z value in engineering calcs & tables of section properties).

What benefit can that construction offer to sacrifice on road safety?

I don't think I'm being too conservative by being alarmed by those arms if they are used on the road.

Bending in which plane are you concerned about? And at what point?

Presuming you're considering plain tube on it's own, you're correct that it doesn't resist bending as well as most other forms. Whichever plane you're bending in, the amount of material in tension or compression isn't particularly impressive.

In this design, considering only the long section attempting to bend in a vertical plane, you will have one complete tube in compression, and one complete tube in tension (plus some strength from the side plates, but I doubt that would add a significant amount). Wouldn't this arrangement have much better section properties than simple round tube?

toughnut wrote:From looking just at the pics I would have thought that the biggest risk point for bending would be just behind the rear axle mount. There is extra bracing in the cup area and I wouldn't think there would be much force in that area compared to the longer part of the arm.

looking at a stock LR arm, that is cast in an I beam section it is solid at the axle rear bush area. The arm is widest or tallest at just behind this bush. So one could hazard a guess at this needing to be the strongest point.

Im guessing that the biggest issue on any vehicle ESPECiALLY a road going one would be heavy sudden braking ie emergancy braking from say 100km/h

I would be interested to see how much the are actually twists within itself during articlulation as it has 2 rubber bushes at axle end and in the LR case a pin end that would offer some rotation freedom at chassis end.

Serg

Yeah. I agree. These are used on comp trucks that hit some pretty large bumps head on so I'm sure in this form its strong enough. Lateral torsion would be taken care of by the mounts so its the longitudinal force that is of most concern and for me it would be the force applied between the chassis mount and the rear axle mount from impacting rock, bumps etc also for on road, under heavy breaking. I don't think there would be enough rotational force from the axle when flexing to cause too many problems.

what about issues with rusting from the inside out if water gets in the tube. it might take 5 years but any rust will make them weaker