The ONSPOT Automatic Tire Chain System offers the traction of a single set of conventional snow chains at the flip of a dashboard switch, 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. This allows 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 rubbercovered chainwheel causes the chainwheel to rotate, creating enough centrifugal force to flail the chains out. (The principle of the system is similar to a small generator driven by a bicycle tire to operate a headlight.)
Six lengths of chain spaced at 60-degree intervals on the chainwheel ensure that there are always 2 chains between the tire and road surface whether the driver is accelerating, braking, or are in a wheel lockup condition. The traction from the chainwheel is obtained in forward or reverse.
When the dashboard switch is turned off, the solenoid exhausts the air provided to the chain units and return springs in the air cylinders bring the chainwheels back to their resting position.
The ONSPOT tire chain system is used in various emergency vehicles as well as large trucks and buses. According to the company, permanent mounting on the system reduces conventional chain mounting/removing time and eliminates wheel well damage from broken conventional chains. Chains also last longer because they are used only when needed.