I put it down to amount of rubber on the ground Vs weight. Also the D3 had just enough scrabble to throw off the mud and get traction.
Seeing what the Pinny did brought back a lot of memories of the army Acco's in the 70's. They did exactly that. We used to call it ski-ing. The only option was, if you could, was to ram a tree before the momentum got up.
