Ground clearance is the figure most often quoted when a vehicle's off-road ability is discussed, and on its own it explains very little. Several other measurements matter more in practice.
What the figure actually measures
Ground clearance is the distance from the ground to the lowest fixed point under the vehicle, usually a differential housing, a crossmember or a skid plate.
It tells you the height of an obstacle the vehicle can pass over without the underside making contact, assuming the wheels can straddle it.
It says nothing about what happens as the vehicle enters or leaves an obstacle, which is where most vehicles actually run into trouble.
Approach and departure angles decide the ends
The approach angle is formed between the ground and a line from the front tyre contact patch to the lowest point of the front overhang.
A long front overhang produces a shallow angle, so the bumper strikes the slope before the tyres can begin climbing it, regardless of how much clearance the vehicle has underneath.
Departure angle governs the same problem at the rear, and a towbar frequently becomes the limiting point on vehicles that would otherwise be capable.
Breakover angle catches long vehicles
Cresting a ridge requires the vehicle to pass over a high point positioned between the axles, and a long wheelbase makes that far harder.
The vehicle can become grounded on its belly with wheels on either side unable to reach the surface with any load on them, which ends progress immediately.
This is why short-wheelbase vehicles remain popular for difficult terrain despite offering less interior space and a less settled ride.
Traction distribution matters more than any dimension
A wheel in the air receives no load, and an open differential sends torque to whichever wheel offers least resistance, so a raised wheel can absorb all of the drive.
Locking differentials, or braking systems that simulate them by slowing a spinning wheel, redirect torque to the wheels with grip.
Suspension articulation reduces the problem at source by keeping wheels in contact with uneven ground, which is why long-travel suspension appears on serious off-road vehicles.
The costs of clearance on the road
Raising a vehicle lifts its centre of gravity, which increases body roll and reduces stability in avoidance manoeuvres at road speed.
Taller bodywork increases frontal area and drag, and off-road tyres add rolling resistance and noise, so the penalty is paid on every ordinary journey.
Air suspension resolves some of this by lowering the vehicle at speed and raising it on demand, which is why it appears so often on vehicles claiming both roles.