I'm at work and Ruby is at home so a pic from the internet is the best I can do at the moment (51 cm 2007 Specialized Ruby Expert Triple). I have custom wheels with 'bullet proof' hubs (hand built MTB stunt hubs!), new rear derailleur, new cassette, fresh crank rings. Had the wheels checked out under a microscope last week and they are perfectly true, no indication of cracks or anything. At the same time, the bike was disassembled and the frame stress tested. Everything is fine- no cracks in the frame or obvious issues. Other than a small saddle bag, nothing else tricked out on the bike. I've had the bike checked out thoroughly by two top flight bike builders/mechanics and no one can seem to identify the problem. this issue has been going on in a minor way since I purchased the bike in 2008 but has gotten more noticeable in the last year (and reproducibly worse when I move the saddle forward)

it happened again this morning.... rolling passively ~14 mph downhill on a 2% grade, spanking new clean pavement. The rear wheel skipped quickly left/right and then hard left. I kept the bike upright but just barely.

this little quirk has cost me 6 broken bones this year- the crash happened under virtually identical riding and road circumstances as above. Having a tricky bike is one thing if I'm putzing around on a bike path. But I ride ultras- crazy distances- and the safety issue is forcing the issue about considering another bike.

maybe I should contact an exorcist

many thanks to everybody