I want to run a derailer on a 24" bmx bike. I don't like the feel of any mtbs out there. (even the so called dirt jumping bikes). Basically all I want is about 7 speeds so I can get up the mountain, I also ride aggressive xc and need a couple of gears to keep up with my bros. Also what about hub spacing? I'm guessing that mtb hubs won't fit, but is there a way to run more than one gear on a bmx cassette? Any help is much appreaciated, thanks