If you do not want to strip the whole lot of the old paint AND providing the the underlying frame is in good condition(no rust), you could get away with roughing up the surface with sandpaper to give the paint something to grab. Then you could dispense with the primer.
If you do not want to strip the whole lot of the old paint AND providing the the underlying frame is in good condition(no rust), you could get away with roughing up the surface with sandpaper to give the paint something to grab. Then you could dispense with the primer.
5-6 cans for a good job + primer.