That "crank loose" feeling when the rear tire breaks traction is one of the reasons I prefer a crank forward, flat footed frame geometry like some cruiser and dutch bikes have. That seating position although less aggressive for "mountain biking" type throwing your weight around does consistently keep more of your weight on the rear traction drive wheel and reduce slipping, also with less weight on the front tire it tends to take less effort for the front tire to cut through fresh snow.