Thread: Dual shock absorbers

Dobbo,

The purpose of a shock absorber in a suspension system is to absorb the rebound energy of a spring after it's been compressed (i.e. to dampen its rebound motion). The absorbed energy is dissipated as heat within the shock.

In normal sealed road operation, the shock absorbers aren't working very hard as the suspension isn't moving up and down very much. On corrugations (and especially at speed), the springs are constantly being compressed and rebounded, resulting in rapid heat buildup inside the shocks. As the oil inside the shocks heats up, its viscosity increases and its ablility to "absorb" the spring recoil energy decreases. This is known as shock fade, and results in "sloppy" suspension characterised by excessive suspension travel and reduced handling.

To then answer your question, in running dual shock absorbers, each shock is only dissipating half the spring energy, so the suspension system is more resistant to shock fade. Also, monotubed shocks are more resistant to shock fade than dual tube ones, as they ecn better "give up" their heat to surrounding air.

Polybags or HD springs with helpers on the other hand are part of the "spring" in a suspension system which is related to load carrying ability of a vehicle. All other things being equal, a vehicle with stiffer springs for example will be able to travel over corrugations with more weight before bottoming out type thing... conversely, an unloaded vehicle with stiff springs will have reduced wheel travel. Choosing spring stiffness should be based on the type of driving the vehicle will do, and its laden weight. It is a compromise between load carrying ability and wheel travel when unladen.

That said, standard disclaimer applies - you have to make sure all other components of the vehicle can handle the extra weight (axles, chassis, braking and steering systems etc).

hope that answers your question.

Cheers

...nehow, hope that's

To add to that with regards to fade, much of it happens in twin shell shocks because the oil airates and the gas is easy to pass through the shock valving in comparison to the oil. These are shocks like Koni, OME, TJM, Monroe, Pedders etc. Foam cell shocks when hot can/will also damage the foam cell (in place of the gas) and the foam breaks down will the same result as airation. The problem with foam cell shocks is that when they cool off they remain in their faded condition, unlike a gas shock that will cool off and return to normal.

Monotubes do dissipate heat well as said, but they also dont notably fade because the oil can not physically airate (gas is in a seperate chamber). I have heard one manufacturer claim that when the get hot (and they can get bloody hot!) that the increase in pressure actually makes them more effective. This style of shock includes those with remote canisters also.

The action of the shock is to control the movement of the suspension. As you continue to stiff (reasonably) you will continue to add control which gives increased traction on rough roads. The greater the weight on the vehicle and so the greater the forces within the springs will result in a need for greater control from the shocks. To get this you get have a single shock valved stiff like what I've done or you can run 2 shocks. The advantage of 2 shocks is the reduced forces within the shock so things like bushes last a lot longer, and better heat dissipation. Its also more cost, fabrication and parts.

The other big bonus of stiff or dual shocks is you will also get body control, and that is something I love. Harsh travelling and no bounce.

Springs is what supports the load in the car, so polyairs or stiff springs will be the way to go to keep it all off the ground. The shocks will just control the action.

Heavy touring vehicle - on the rear stiff springs, polyairs and stiff or duel shocks.

Oh, to answer your question. Max has duals on the front. He can tell you the story as there is a bit to it.

Dobbo,

Would definately recommend twin shocks on 110's, I have done quite a few now and feedback is that improvement in control, laden on continued corrugations etc in high ambient tmps etc is vastly improved. All have said well worth the effort/ cost etc.

JC

I'm running dual shocks on my 85 V8 County. I put them on after having trouble in the Simpson Desert with it bouncing on the corrigates on sand dunes. This made a huge improvment in the handling of the vehicle. I'm running them with HD King springs. My truck is also a 120 extra cab with an ex telstra body on and is fully loaded all the time with the camping gear and 430L of fuel. It wasn't hard to do just a little time consumming in taking out the fuel tank to slug the holes on the LHS and making the brackets and welding to the diff housing.

Can you secure (by the lower pin on the standard shock) a bracket for the second shock mount?

Save welding the rear axle

sorry it makes sense to me but I am endeavouring not to be a binge drinker.

What are you doing to need twin shocks?,if you are going that hard why not fit a set of Koni Raids,Monaco Performance,just down from All4x4 spares have the best price. Pat

You could make a bracket like that I suppose but I think that I would have bent it in the bush by now, but my truck does get knocked around in the bush a bit because of the type of trails I drive