To give the Farmer's answer- Nothing is good driving over wet feilds! Causes the ground to be ripped up and panning. However! Low tyre pressures , more surface area, less ground pressure , so you don't sink. Though my experience over the years, if there's no friction bettween tyres and surface, you ain't going anywhere! I'm not suprise the load over the back axles makes all the difference. Most Land Rover pick up backs, and any other pick up or van for that matter are designed to run with a load, no load no weight no traction. Snow tyres work because the snow packs into the tread, and snow sticks to snow. Provided (Shades of Brtitsh Rail) it is the right type of snow! If you have a hard packed smooth surface , just go sleding or skating.