ARMY BASICS

The HMMWV (High Mobility Multipurpose Wheeled Vehicle, pronounced “Humvee”, or Hummer for short) was designed for military use over rough terrain.

Civilians can now buy smaller versions of the original aircraft-carrier-sized Humvee. All Hummers have a low centre of gravity, a powerful engine and clever technology to help them stay the right way up.

BREAK IT DOWN

In mud, flat, squashy tyres give more grip and better handling. In a Hummer, the driver can pump the tyres up or down automatically using a switch on the dashboard. The self-levelling suspension system also allows its wheels to tilt on bumpy ground while the body remains level.

Powerful gas-filled shock absorbers allow the wheels to rise and fall independently over bumps. Even if some wheels are spinning in mud or in mid-air, the Hummer can still get itself out of trouble. It uses differential action to redirect the engine torque away from the wheels that have no purchase, feeding more to the wheels that can still grip — and so powers itself free.

SUPER-STABILITY/ STICKING POWER

Like anything else, cars tend to topple over if their centre of gravity is too high or moves too much to one side. The Hummer’s squat design gives it a low centre of gravity, allowing it to tackle slopes of up to 60 degrees.

The tyres don’t slip, thanks to chunky treads up to 13mm (0.5in) deep, at least 50% deeper than on normal tyres.

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