When they are racing on the dirt bikes you can see they have normal dirt-bike straight across handlebars but in the close ups shots of the actors you can see they have street bike curved handlebars and speedometers.
It's unlikely that the lady at the diner would have needlessly spent both barrels of her shotgun (especially since the toughs were already fleeing as it was, and so she would not have needed to empty the last barrel after them to scare them off), since the bikers might hear both shots (even over their roaring bike-engines) and thus know that the gun was empty, and that they therefore would be able to safely return and overpower the owner before she could reload.