About this time last year, I began riding and wrenching bikes when I (over)paid $40 for a POS Puch Cavette ... it formerly belonged to a homeless man and nothing worked but I had a lot of fun learning with the bike as I got it in working order.
A few months later, I lent it to my friend and he returned it with the rear derailleur shoved so far into the spokes that all I could do was laugh. I am a poor college student so it spent a good amount of time as a single speed with the chain fixed to in reasonable gearing.
Eventually, I saved up some money and decided I want to be a hipster ******bag so I invested in a DT Swiss deep-v rim which I built around a Surly flip-flop hub and an aluminum IRD crankset... it was the best decision I have ever made. Frankenbike-ish as it may have been, the final product was my baby and it has left me with a soft spot for fixies build on vintage frames.
I bought the upgraded parts with the intention of investing in a nicer frame set some day... unfortunately, that day has come much sooner than intended. After lending my bike TO THE SAME FRIEND, he returned it like this...
He claims he was casually riding and it just happened... the chain was still intact but obvious it was off the cogs... the rear tree is so bend that the wheel was jammed against it. Luckily, somehow only the frame is damaged.
My questions are...
1) How the **** does this happen? I realize that a fixed gear has considerably more torque than this 12 speed frame was intended for but the above damage seems absurd.
2) What do I avoid in my next frame purchase? Is this just due to damage to the frame that went unnoticed... or are there some frames that should never be built into fixies?
3) I am certain that my Puch had BSC threading and I know that the bottom-bracket was square tapered because I bought those pricey squared tapered cranks to fit. What do I need to look for in a frame to make sure the cranks fit? Can it be Italian threaded? Or are there differences in the standards for bottom-brackets that limit me to a frame with BSC threading?
4) Anything else I am too ignorant to ask?
Basically... I would appreciate it if anyone could help me learn what I need to know while looking for a new frame. I have learned quite a bit about bikes but almost entirely from doing. I know "Google it" is a popular answer for easy questions on here but to be honest, I don't want to overlook some compatibility issue and wind up with expensive (for me) parts that can't be used.
Thanks! I apologize in advance for inevitably irritated half of you with this post.