Mountain Bike Rear Derailleurs
Shimano M670 SLX 10 Speed Rear Mech$24.78RRP: $55.77Save 56%
Shimano Deore M591 9 Speed Rear Mech$30.36RRP: $49.56Save 39%
Shimano Deore M592 Shadow 9 Speed Rear Mech$35.94RRP: $49.52Save 27%
Shimano Deore M615 Shadow+ Rear Derailleur$37.13RRP: $61.97Save 40%
Shimano SLX M675 10 Speed Shadow+ Rear Derailleur$37.17RRP: $68.11Save 45%
Shimano SLX M662 Shadow 9 Speed Rear Mech$40.28RRP: $61.97Save 35%
Shimano ZEE M640 Shadow+ Rear Derailleur$43.38RRP: $74.32Save 42%
Shimano XT M781 10 Speed Rear Mech$45.80RRP: $74.36Save 38%
Shimano XT M772 Shadow 9 Speed Rear Mech$54.53RRP: $74.36Save 27%
Shimano XT M786 10 Speed Shadow+ Rear Mech$54.53RRP: $86.71Save 37%
Shimano M780 Shadow 10 Speed Rear Derailleur - Silver$54.53RRP: $86.77Save 37%
Shimano XT M771 9 Speed Rear Mech$58.25RRP: $74.32Save 22%
Shimano XTR M980 Shadow 10 Speed Rear Mech$74.32RRP: $154.94Save 52%
Shimano XTR M972 9 Speed Shadow Rear Mech$109.02RRP: $210.72Save 48%
Shimano XTR M986 10 Speed Shadow+ Rear Mech$110.31RRP: $173.53Save 36%
Shimano Saint M810 Shadow 9 Speed Rear Mech$111.50RRP: $136.34Save 18%
Shimano XTR M9000 Rear Derailleur$154.94RRP: $185.92Save 17%
Sram X01 11 Speed Rear Mech$185.92RRP: $247.91Save 25%
Sram XX1 X-Horizon Rear Derailleur$235.46RRP: $307.42Save 23%
The rear derailleur, or rear mech as you will more often hear it called, is the device on the bottom rear right hand side of the of the bike frame which moves the chain up and down the cassette on the back wheel, i.e. changes the rear gears. It is operated by a cable which pulls the mech a certain distance into or away from the frame depending on the amount of force used to pull or release the cable. All rear mechs these days are ‘indexed’ in that the mech moves the chain a fixed distance up or down the cogs with one push of the gear lever.
A rear mech has a main body which contains the spring and frame bolt and a pivoting cage containing two jockey wheels underneath. This cage is available in three lengths: short, medium or long; with the general rule being the higher the number of teeth on the largest sprocket at the back the longer the cage you will need, i.e. 34 tooth equals long cage whereas 21 should use a short cage etc.
The rear mech is mounted to the frame via a ‘hanger’ which is usually bolted on, making it easily replaceable and designed to break off in the event of a crash to prevent damage to the frame. Shimano now make a Direct Mount version which is bolted directly to the frame without a hanger and is more common on bikes with a bolt through rear axle.
There are two main companies which produce off-road rear mechs; Shimano and SRAM, which although look and operate very similar are unfortunately incompatible with each other’s systems. This is because each system has a certain amount of movement from the gear lever and differs slightly with each manufacturer. As an aside, they do work with each other to a certain degree but it is not as slick and not recommended for long term use.
You can mix rear mechs from the same manufacturer as long as they are designed for the same number of gears, i.e. you can use a 10 speed Shimano XTR rear mech with an XT 10 speed groupset as they are both 10 speed compatible. Some older rear mechs will work across different numbers of rear gears but it can be tricky to set up and so always easier to run a matching mech with the specified amount of gears.
Shimano are the world’s biggest cycle groupset manufacturer making rear mechs for all types of bikes and riders. From professional riders to shopping bikes, Shimano make a rear mech for it.
The hierarchy of Shimano off-road rear mechs from professional to entry level is as follows:
Downhill / Freeride
SRAM are the newest groupset manufacturer and have come up with a series of ingenious inventions which have quickly gained a wide fan base from professional to recreational with their alternative view on operating systems.
The hierarchy of SRAM off-road rear mechs from professional to entry level is as follows: