Approach, Departure & Breakover Angles

Overhang is measured horizontally from the tire contact patch to whatever hangs lowest at that end — usually the bumper, sometimes a tow hitch or an exhaust.

What bigger tires actually buy

Half, not all

Fitting tires two inches larger in diameter raises the axles by one inch, not two — the axle sits at the centre of the wheel, so it moves up by half the diameter increase. Going from 31 to 33 inch tires is an inch of clearance, and it is worth roughly two degrees of breakover on a short-wheelbase vehicle.

A suspension lift is the opposite trade. It raises the body and frame, improving breakover and departure, while doing nothing at all for the clearance under the axle and the differential — which is usually the part that actually grounds. It also raises the centre of gravity, and the tip-angle figure above moves in the wrong direction as it does.

Where the numbers come from

Approach and departure are the angle between the ground and the line from the tire contact patch to the lowest point of the overhang — pure trigonometry, and set by overhang length as much as by height. It is why a serious off-road vehicle has such short overhangs, and why a long front bumper ruins an angle no amount of suspension can rescue.

Breakover assumes the low point sits mid-wheelbase and the vehicle pivots on the ridge with a wheel on each slope, so the ridge angle is twice arctan(2 × clearance ÷ wheelbase). On a real vehicle the low point is rarely exactly central, which is why a manufacturer's published figure usually comes out a degree or two worse than this calculation.

Things worth knowing

• Bigger tires raise the axles by HALF the increase in diameter, because the axle sits at the centre of the wheel. Going from 31 to 33 inch tires is one inch of clearance, not two.
• A suspension lift raises the body and the frame but not the axles or the differentials, so it improves breakover and departure while doing almost nothing for the clearance under the axle — which is usually the thing that grounds.
• Approach and departure angles are set by overhang as much as by height. A long front bumper ruins an approach angle that suspension cannot rescue, which is why serious off-road vehicles have such short overhangs.
• Breakover is the angle people discover last and remember longest, because grounding the belly on a ridge takes the weight off all four wheels at once and there is nothing left to drive with.
• The static tip angle is where the vehicle goes over on a perfectly smooth slope with nothing happening. Every real side slope has bumps, ruts and a driver, all of which arrive well before the arithmetic does.