I have sun ez3 trike,it has rear freewheel with the largest being 28 teeth,can I put a mega range with 34 teeth on it,and do I have to change the deraileur.Objective to make hills easier.
You do not indicate if this is the SX ("tadpole model" weighing 48 lbs) or the USX HD (weighing 65 lbs.) (Either curb weight is a challenge but if you've been spinning away at 80 or better rpm, I say "reward yourself with a lighter trike." Review the archives at http://www.rtrmag.com - Recumbent and Tandem Rider Magazine or The Recumbent Journal for alternative rides.)
Alternately, ask your LBS for an install of a 28 or 26 tooth chain 5-bolt chain ring that could provide 5% lower gear to pull hills. The Microshift FD will accommodate a granny gear change down to 26t ring but will not shift nicely with a 24 t. IF this EZ-3 is the USX HD, do not expect much improvement or success on inclines as the drive applies only to the right rear wheel and you'll be frustrated by its "crabbing to the right" while you're spinning frantically and working to redirect the steering.