Ideally, all four tires should use snow chains, but the minimum requirement to drive in extreme winter environments is that at least the two wheels that connect to the drive train system are covered in chains. Front-wheel drive vehicles require chains for the front wheels while rear-wheel-drive vehicles require chains for the rear.
Snow tires do not provide the much-needed traction on icy conditions. Tire chains are able to dig in deeper through the ice to help catch more traction. Vehicles with snow chains are only able to travel a maximum of 40 miles per hour.
Neglecting to mount snow chains on the wheels that connect directly to the drive train can be lethal to the driver. When a front-wheel-drive vehicle does not have snow chains on the front tires, the driver will have difficulty steering. Failure to mount the chains on the rear tires of a rear-wheel-drive vehicle can cause it to fishtail when turning, resulting in the driver losing control of the vehicle.
Regardless of the type of drive train system a vehicle has, chains on all four wheels offer the best traction. When chains are mounted on every tire of the car it will be able to retain its balance and geometry.