You change gear like you do on a normal hub.
Its not properly fixed if you get what i mean. Theres some kick back on it, so if you stop pedling your legs will still be pushed around, but theres abit of slack there if you get what i mean. Which means that you can change gear.
I dont think your ment to skid with them, or ride them without a back brake are you? Or something like that. Thats how i understood it anyway.
Werent the old ones modified so you had a sort of nutral so you could stop pedling on fast downhills.
I seem to remember there is a myth or a fact that they were stop being made because people did this neutral modification and a few people went over bumps, it jumped into gear and they were thrown off. That was either a myth or a fact, not sure.
Im sure there is/was the person on here who has the last 3 speed fixed hub made by SA when they were first doing them?
They do different shifters on them aswell, which is pretty good.