For wheels without joints, climbing obstacles will cause the body of the vehicle to tilt. If the weight of the vehicle moves outside of the wheels, the vehicle can tip over because of "static instability". At high speed, a vehicle's inertia can cause it to become "dynamically unstable". This means it can be tipped over by a smaller obstacle, or simply by turning or changing speed too quickly. Without jointed limbs, it can be impossible to recover from being tipped over.