Do you refer to single track trails as dirt? If so you might want to rethink fixed MTBing. On smooth trails it can easily be done but on the majority of trails I've seen riding fixed would be near impossible. I've heard it referred to as having a learning curve beyond jedi... I guess this means it's hard. Seriously though in my region, on the trails I ride you MUST be able to coast. Catching a root or rock while pedaling would be dangerous. Some of these trails are average easily ridden trails others are a little or a lot more difficult. I don't see any way to pedal through some sections without crashing, breaking the pedal/crank or breaking my foot. Obviously fixed bikes have been driven on dirt paths/trails but on even lightly techy trails... I wouldn't recommend it.