I'm having a new rear wheel built for my tandem and although it's only a 7 speed I've opted to get a new hub with a 9 speed freehub body [to allow future upgrades]. I know I'll need a spacer to make a 7 speed cassette work but do I also need a 'dork disc' to prevent spoke carnage if my cheapo derailleur overshoots the innermost gear? If I do need one, where should i find one? I saw some on eBay but is this the kind of thing my local bike shop should be able to hook me up with, and what should i be looking to pay? Any advice is welcome as I'm kind of pretending here; I really don't know much about various drivetrain components and jumping into this is my method of learning. Thanks in advance. Dean- I didn't see a "Mechanics" forum, is this the best place to post this?