The subframe is a critical part of any expedition vehicle build. It is the interface between the vehicle and the habitation module.
It needs to serve two critical functions that are almost contradictory.
It needs to hold the habitation box securely to the vehicle while remaining flexible.
Most large offroad vehicles utilise a ladder chassis design. This comprises of two 'C' section rails that are joined by cross members. You then bolt all the components that make up the truck to this substructure.
By design, the ladder chassis will flex/twist. This acts as a secondary shock absorber that protects the vehicle's components. It also adds articulation in the axels, increasing the offroad capability of the vehicle.
So what happens if you use a rigid subframe?
If you don't decouple the habitation module from the torsional forces applied to the chassis during offroad use, you have two main issues.
Firstly the habitation body module acts as a "splint" to the chassis and limits its articulation and, therefore its offroad performance,
Secondly, and more importantly, those torsional forces are then applied to your habitation module structure. This will put significant loads onto the habitation module, and it will end up prematurely failing. This could be a minor failure such as water ingress or major failure like fractures that would render it unsafe for road use.
So what is the solution?
The solution is a dynamic fixing between the chassis of the vehicle and the subframe.
At Motorcraft, we offer two solutions. A rail on rail subframe and a four-point subframe.
Rail on Rail
This consists of two rails positioned on top of the chassis. These are rigidly fixed at the rear of the vehicle and then fastened at the front with spring bolts.
Cheaper to manufacture
Better load distribution onto the chassis
Limited travel by spring bolts means a more rigid structure
Reduces flex in the chassis and therefore articulation
corrosion between the rails due to debris ingress
Our four-point torsion-free sub fame utilises three pivot points attached to the chassis rails at four positions. A pivot at the front and the rear of the chassis that is mounted longitudinally. The third is in the centre mounted laterally.
Almost unlimited amounts of free movement
Ultimate off-road performance
isolated load distribution
expensive to manufacture