Not quite a Mullet, but I do run a few bikes (DeKerf UK Ltd, DeKerf Singlespeed, Fisher Sugar Team, Breezer Jet Stream) with 26"x2.5" Vittoria Mota tyres at the front and 26"x2.2" Schwalbe Nobby Nic's at the rear, giving a larger effective diameter at the front (with seemingly infinite grip).