Engineering:Turning circle

Turning radius of a passenger car - wall-to-wall radius / diameter at the top, taking the front overhang into consideration, and curb-to-curb radius / diameter at the bottom.

Turning circle refers to a theoretical minimal circle in which a vehicle or boat can be turned around. The tightest turning circle possible for a vehicle is the one where the vehicle does not move either forwards or backwards while turning and effectively simply rotates on its own axis. Taking a rectangular vehicle capable of doing this, its turning circle would in fact be equal to the diagonal length of the vehicle. Most obviously boats can be turned in this way.

With wheeled vehicles with normal steering (i.e. one or two or even four wheels at the front capable of steering), the vehicle's turning circle is a measure of the space needed to turn the vehicle around while the steering is set to its maximum displacement from the central 'straight ahead' position - i.e. either extreme left or right. If a theoretical marker pen was placed on the point of the vehicle furthest from the centre of the turn, it would draw a circle and the diameter of that circle would give the value of that vehicle's turning circle when measure using one's preferred units, imperial or metric.

For example the 2017 Audi A4 has a turning circle of 38.1 feet (11.6m).

Kerb to Kerb Turning Circle

Further information: Turning radius § Curb to curb

The kerb to kerb turning circle is smaller than the turning circle as it refers to only a partial circle (~180°) with the vehicle alongside one kerb to start with. To perform a U turn in a forward direction only, the centre of the turn is not coincident with the centre of the road - thus a complete circle would not be possible (without driving onto the pavement to complete the manoeuvre). It also does not take into account that part of the vehicle that overhangs the wheels where as 'turning circle' does.

Common uses

• Aeroplanes
• Watercraft
• Wheeled vehicles

See also

• Breakover angle
• Minimum railway curve radius
• Overhang (automotive)
• U-turn (maneuver)