Or 40? I've looked around a bit and haven't seen a track cog more than about 22 teeth. It seems that witha flip/flop hub, one could simply screw on a large track cog and motor on. Sure, the threading is then reversed, but shouldn't the lockring then still lock it down? no fuss, no muss, and all those bolts and steel and rubber eliminated. The only real trouble is how much a track cog otherwise costs these days since the whole "fixie" thing came along. I think they were about $5 back in the 70's when I rode a little track.