swing arm bracing


I've seen alot of extended swing arms with bracing but some without, is there a certain length that bracing is required. what about swing arm extensions, i want to add some this winter but don't want a weak link because of it.
Some say if you go over 4" you should get it. talk to the pros like Trac Dynamics personally I think if you go over 6" you should get it.
that's always been a tough one. Has any one measureed the actual deflection with/without bracing? What's optimal and what's not? Is the bracing to prevent twisting?

hillclimbers have amazingly long arms and I haven't personaly seen any break.