They are designed to get you off your driveway, or where you get stuck, but must be removed immediately you hit tarmac. Handy as a back up if you get stuck, but will tear on tarmac. When I worked for British Gas some time ago we carried a sprung bar clamp which opened to put 4 metal bars across the tyre to get you out of a drift, but they were heavy to carry around. The socks are a new cheaper alternative and no weight or space in the boot.