Re: 16 Tooth Sprocket
i've run a 28 tooth on my bike with 24" wheels. unofficial school speed trap reading 48mph. unfortunately, when my chain broke, it ripped the teeth off the sprocket, so now i'm back to a 30 tooth.
i've got heavy duty worksman wheels with Jim's sprocket adapter, and with the 28 my chain was really close to my spokes. might be able to squeeze a 27, maybe even a 26 on there, but that's about the clearance limit for me.
if you're looking for a 25tooth, try modifying a BMX sprocket.