The claims. Tyre Grip creates a "better grip on snow, ice, and slush" by providing "an adhesive surface that grips the roads." You spray it on tires, and it's supposed to work for up to 50 miles ...

Winter grip slips. Deep grooves and an array of small slits, called "sipes," help most new tires bite into snow. Shallower tread and worn-away sipes reduced snow grip markedly for our half-tread ...