The ONSPOT Automatic Tire Chain System , from ONSPOT of North America Inc. offers the traction of a single set of conventional snow chains at the touch of a button, without having to stop the vehicle. An electric switch mounted in the cab provides 12 volts to an air solenoid mounted on the vehicle's frame rail. Compressed air to the solenoid is supplied from either the vehicle's onboard air system or a 12-volt compressor kit. When the dashboard switch is activated the solenoid opens, allowing compressed air to enter the air cylinder and lower the chainwheel so it contacts the inside of the tire. The friction between the tire and the rubber-covered chainwheel causes the chainwheel to rotate, creating enough force to flail the chains out in front of the tire. Six lengths of chain spaced at 60-degree intervals on the chainwheel ensure there are always two chains between the tire and road surface.