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Ridden: Shimano RD-M985 XTR Shadow Plus rear mech

  • By Ben Marchant
  • Published Apr. 11, 2012
  • Updated Oct. 11, 2012 at 4:51 PM EDT

Rear derailleurs have been around for over 100 years yet essentially the rear mech hasn’t changed much since Suntour invented the slant-parallelogram design in 1964. Shimano introduced the Shadow mech in 2009, designed to produce a derailleur which had less of a profile for catching on trail-side obstacles and ruining your day.

The Shadow Plus, however, is an entirely new mech tensioning system governed by a clutch which allows you to increase the tension on the chain.

This results in fewer dropped chains. Prior to now the most common way to deal with this has been through chain devices (and these are nothing new to the gravity end of the market in particular). They are also becoming more and more common in cross country as riders realize the benefits associated with fewer dropped chains.

Chain devices do not work that well with front mechs though as the whole point is to stop the chain from wandering off the chain ring. A front mech is designed to do just this. The Shadow Plus utilizes a simple clutch type system with an on/off switch.

Switch to on and the tension on the mech is increased dramatically. Moving the mech by hand at all is difficult, and on the trail it virtually guaranties that the chain will not come off.

It also has the added benefit of reducing the noise from chain slap. This sounds like a really small thing but actually it is really noticeable on the trail. I also wondered about how much better this was for my carbon frame that the chain was not bouncing off it all the time, a small point but interesting nonetheless.

Switch to off and the chain tension reduces to that of a normal mech allowing you to remove the wheel easily.

Okay, $250 is a lot to shell out in the interest of a quiet bike and reducing the chances of your chain dropping but the system does actually work. Shifting action is slightly heavier when moving up the cassette but that is to be expected, the system still has that smooth shifting action that Shimano is known for.

I had been considering moving to a single ring 1×10 setup with a chain guide for cross country racing but having ridden this, why bother? Sure there is a weight penalty (roughly 32 grams over a standard XTR Shadow) but the benefits outweigh the drawbacks on this one and the pros would seem to agree, as they have been adopting it rapidly.

SRAM too has recently announced a new mech type similar to the Shadow Plus called the Type 2 which should be available in August on X0 and X9. The really good news, though, is that the technology is coming to XT and SLX levels later this year at much lower price points than XTR.

The actual tension of the clutch can be altered using a little key that sits on the P-knuckle or joint just below the switch. As the system beds in it can be useful to fine tune the tension, much like you would tension a shifter cable after a few rides. Not all riders may feel the need to do this but it is a nice design feature. For those long distance riders for whom the increased shifter tension may be annoying it is handy to be able to reduce the tension a little too.

The application of this type of mech is unlimited in the world of mountain biking. Cross country, Enduro/Super D, downhill, trials and street riders are all going to appreciate the advantages this has to offer and in a short period of time we will be wondering what we did before it was introduced. I for one was thoroughly convinced after just one ride and my enthusiasm for the system has not reduced with time.


Ben combines work as a qualified mountain bike guide with reviewing and rating products for Singletrack.com as well as Outsider magazine and Spoke.ie and is also working on a PhD in tourism and entrepreneurship.  With 20 years of mountain biking behind him, Ben remembers the Girven Flexstem, U-brakes and the first time he saw a suspension fork with a 1-inch piece of elastomer in it. He has ridden bikes on four continents and has covered events as diverse as the 2007 mountain bike world championships, the Giro D’Italia and the Single Speed World Champs and lives in Dublin, Ireland.  He is happiest riding technical singletrack and was an early adopter of the 29er… for a European. Find him on Twitter: #spoketweets. Check out all of Ben’s stories.

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