I just turned my old mtb into an Xtracycle http://www.xtracycle.com/html/home.php. I love the thing but I think it needs a new rear wheel now to carry the load and I was wondering if I could get some recommendations. It's a 7 speed setup (can I just add a spacer to an 8/9 speed hub?) and I was hoping to keep the price under $70. I know I could spend hundreds if I wanted to but I'm hoping for a good strong plain-Jane wheel in that price range. I plan on mostly urban riding but fairly agressive. Also, I was wondering if 32 spokes would be sufficient or if I should go with 36. Anyone out there know wheels?