Rear DR snap off?!?!
 

I was cycling along across the roughest bridge around (large expansion joints) amd I change from 5th to 4th and wammo: this happens...... is this normal? it locked up my rear wheel and wrote off 2 spokes.... had the bike since late November and its done 2000-2500kms. I was doing about 30kmh at the time.....

and the spoke damage

and a pic of where the DR broke off....... oh yeah those tyres in the fotos are my new Michelin Pro-Race.....pity I cant use them at the moment..... and the red tyre is my brothers bike.....

Ouch! Stress fracture at the DH mounting bolt caused by overtorquing possibly? Or it's just simple metal fatigue at the mounting hole threads. Maybe pick a replacement hanger with a little more meat near the holes. At least the DH is replacable. What model bike is it? Shame about having to rebuild that wheel though.

Its an apollo RD Z2000 www.apollobikes.com

Rebuild the wheel you say? or can I just replace the spokes.....

My LBS has had a few Al bikes with snapped derailleur hangers. Al is just not strong enough for the job, which is why better ones have replaceable hangers.
To save the hanger from over-stressing, use a breakaway bolt, which will snap before the hanger.
If this happens far from home, it is the kind of situation where you would rejig the bike as a singlespeed, thanking yourself that you opted for horizontal dropouts to tension the chain.

What is a horizontal dropout?

Brendon
:beer:

Maybe it should be called a slideout. :D

A horizontal dropout is just as its name implies. It allows you to slide the wheel straight out horizontally as opposed to diagonally or vertically to the front as in "normal" dropouts. The advantage here is that if you do have a rear mech failure and need to convert to a singlespeed (or double/triple as the case may be depending on your crankset), being able to adjust the position of the rear axle (and consequently the chosen rear cog) allows you to properly tension the chain.

The way I understand it, a horizontal dropout looks like a regular rear dropout tilted on its side a little (hence the term "horizontal"). An example of a really horizontal dropout comes to mind as a track bike. These aren't really "dropouts" though. Most horizontal dropouts that I've seen aren't completely horizontal - instead they are just tilted at a good angle compared to normal. Having horizontal dropouts allow for the setting of the correct chain tension when converting to singlespeed.

-Moab

I was typing when Khuon posted. you can find some pictures of dropouts at Sheldon Brown's site website if you scroll down to "dropout."

-Moab

No, it's more like a dropout tilted on it's side all the way.

I've also seen bikes with truly horizontal dropouts that are rear-facing. I wonder how that works in practical terms. Do you just make sure there's enough slack in the chain to allow you to remove the wheel? Do you have to be in small/small gearing to do it? Admittedly the bike I saw had a pretty short dropout.

I had this happen a couple of months ago on my cross bike. Not fun is it?

Those are called fork ends (yes, the ones in the rear are fork ends) and are found on single speed and fixed gear bikes like track and BMX bikes.

Yeah, I vaguely remember from my youth having had them on my BMX bike. However, I didn't have a QR on my BMX. I've seen this style fork-end on a roadbike and was wondering how one uses it in conjunction with the QR.