Right Driver

How are approach, departure and breakover angles measured?

Off-road vehicles have several important measures by which their competence on rough ground is assessed. Wading depth is one – how deep can water be before it gets into the engine and leaves you stranded in the middle of a river. Maximum gradient is another – what’s the maximum angle of slope you can drive on before you risk tipping over. But the most commonly cited figures are approach and departure angles and, to a slightly lesser extent, ramp breakover angle.

The approach angle is the maximum immediate change in angle that the front of a vehicle can cope with when approaching an uphill slope or leaving a downhill slope.

The departure angle is the maximum immediate change in angle that the rear of a vehicle can cope with when exiting a downhill slope onto flat ground or entering an uphill slope.

You can see that in the following two diagrams that approach and departure angle are affected by how close to the corners of the vehicles that the wheels are. This is determined by the wheelbase in relation to the overall length. The wheelbase is the distance between the two axles, or the centres of the front and rear wheels.

Short front bumper gives a better approach angle. Short wheelbase in relation to height gives a better breakover angle
The bumper position is slightly better for this long wheel-base SUV, giving it a slightly superior departure angle

The purple lines describe the breakover angle.

As the track flattens out, this SUV risks rubbing the underside of the vehicle on the slope. This is the ramp breakover angle
A good illustration the departure angle – the back of this off-road vehicle is high with no overhang, so the vehicle can approach a very steep slope, assuming that the centre of gravity isn’t so high that it tips over backwards.

Darren has owned several companies in the automotive, advertising and education industries. He has run driving theory educational websites since 2010.

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