The Definition of Ground Clearance
This is an important element in an All-Terrain 4WD and has been taken at ‘ face ’ value over the years . Every vehicle manufacturer provides a Ground Clearance number in mm as part of the specification , but has anyone wondered how this is measured ? To do this , let ’ s review and understand some of the definitions and revisit some basic principles .
In general terms , ground clearance is the measured distance between the undersides of the vehicle to the surface the vehicle is resting on . This definition is not acceptable from a technical perspective due to the following factors ;
Surface
First and for most the surface must be level for an accurate measurement .
Vehicle Suspension and axles
Vehicles with independent suspension ( with no fixed axles ) can have varied ground clearance as the sprung load is varied . Whereas vehicles with fixed axles are most likely to have the fixed differential as the lowest point . Even with varied loads , the distance between the differential and the ground remains the same .
Vehicle body design
Each vehicle has its unique characteristics in body design and that includes the layout underneath the vehicle . That includes the exhaust / silencer routing , suspension geometry and axle type .
Vehicles accessories and components
Items like bulbar / rear bar mounts , auxiliary fuels tanks and underbody bash plates can also affect the ground clearance of a vehicle .
Tyres .
The aspect ratio ration of the tyre and the pressure can contribute to the ground clearance of the vehicle .
The factors above demonstrate the need to have a tighter more specific definitions around ground clearance . In fact there are 4 main definition provided by the Australian Design Rules ( ADR ).
1 . FRONT AXLE CLEARANCE AND REAR AXLE CLEARANCE – the vertical distance from the level surface on which vehicle is standing to the lowest point on the ‘ Axle ’ differential ( when applicable in case of a front ‘ Axle ’) of the vehicle .
2 . GROUND CLEARANCE – the minimum distance to the ground from the underside of a vehicle excluding its tyres , wheels , wheel hubs , brake backing plates and flexible mudguards or mudflaps .
3 . RUNNING CLEARANCE – the distance from the surface on which an unladen vehicle is standing to the lowest point on the vehicle excluding unsprung mass .
4 . SUSPENSION CLEARANCE – the minimum dimension measured from the front and the rear suspensions to the ground .