A mech hanger, derailleur hanger or dropout is a metal connecting component that acts as a bridge between your bike frame and your rear derailleur. It is designed to bend or break on impact in order to protect your frame from, what could be, terminal accidental damage.
Aluminium frames can be quite brittle and prone to snapping, while old school steel frames are less likely to snap and can be bent back within reason if damaged.
Carbon frames, although compliant like steel, tend to be built to be stronger in certain directions and still need protection in the weaker areas around where the derailleur attaches.
Mech hangers are often completely ripped off when an errant stick goes in the wheel, ahead of the derailleur, before being swept back by the spokes ripping the derailleur right off snapping the mech hanger in the process (see picture below).
More common perhaps is a lateral blow from an impact with a rock or tree which bends the mech hanger out of line, thereby throwing your gears out of index. This can be very difficult to fix out on the trail (although your local bike shop may be able to straighten it if it is not too badly damaged) .
Another case that we often see is where riders drop their bikes down heavily on the transmission side and the derailleur hits a projection on the ground such as a stump or a rock. The mech hanger is bent and the gears thrown out. To avoid this, get into the habit of laying your bike down “gears to sky.”
Singletrack School coaches report that they bend or break a mech hanger about once or twice a year.
Damaging your mech hanger out on the trail can mean the end of your ride. Not a massive problem out on your local trails, but if it happens at the highest/furthest point on a trail centre or back country ride, you can find yourself in an escalating situation; particularly when lightly equipped in poor weather and fading light.
It is possible to remove your derailleur completely and temporarily single-speed your bike, but this is tricky, requires more tools and skill and is only really practical with hardtails. It’s only a “get me home” solution in any case.
It is therefore good practice to carry a spare mech hanger. It’s an easy task to replace your mech hanger on the trail with just an allen key (see picture below). Mech hangers themselves are very light and don’t take up much space in your pack. Just remember to make sure you’re carrying the correct spare for the bike you’re riding.
Your local bike shop is the best place to source your spare mech hanger, although there are also several online services that can help you find that rare or out of production hanger. We recommend gearmechhanger.com.
Replacement mech hangers cost from £10 to around £25 depending on the make and model of your bike. A small price to pay considering the potential hassle a broken hanger may cause.