Second to shifting, chain management is the most important job a rear derailleur has to perform. Today’s ultra-light long-travel trail bikes have us riding rougher trails, faster – all factors which collude to pop chains off both the cassette and chainrings. Enter Shimano’s new Shadow Plus design, which allows the sprung lower pulley cage to be ‘locked out’ below its parallelogram linkage, dramatically reducing chain movement.
Shadow Plus was unveiled at this year's Sea Otter Classic on Shimano's latest XTR M985 rear derailleur. At the launch, Matt Robertson, Shimano’s mountain bike product manager, made the bold claim that if you’re an aggressive trail rider, the new design will "change your life". While we wouldn't go that far, our initial ride impressions suggest that Shadow Plus will be a big improvement for riders who have problems with chain slap, suck and drop – so long as they have deep pockets.
Ride performance
We noticed three things straight out of the gate after our first couple of shifts with the new XTR derailleur: shifting is notably heavier than with previous XTR rear mechs, the action is incredibly precise at the business end, and the new design makes the drivetrain incredibly quiet. Chain slap is virtually non-existent on all but the hardest hits.
The lever requires a much harder push with your thumb than previous Shadow derailleurs, to the extent that we really felt the difference, in terms of tiredness, after a three-plus-hour ride. This extra effort is something any rider can, and will, adapt to should they see the benefit of the derailleur’s improved chain management.
The Shadow Plus derailleur features an on-off switch for the lower pulley cage's friction ratchet
The usefulness of this technology will definitely vary from rider to rider. It's unlikely to appeal to cross-country racers, and it might not even be for every trail rider, as it’s slightly heavier and slightly more expensive than the standard XTR M980 rear mech. The litmus test is likely to be how much chain slap, suck and drop affects your riding.
If you're constantly dropping chains or already have some sort of shift guide on your rig — like e*thirteen’s DRS or MRP’s LRP — then Shadow Plus may be just what you're looking for. If not, you might prefer the lighter action of Shimano’s standard derailleurs.
For those trail riders who wish to use a triple ring crank the Shadow Plus derailleur will likely prove the best possible chain management option, if merely for the fact there are very few triple type guides.
For single-ring trail riders, the new XTR mech should offer better consistency than ultra-light top-only chain guides like e*thirteen’s XCX or MRP’s 1x. However, cost is likely to be a major stumbling block: at US$249.99, it would be cheaper to buy a standard XT Shadow rear mech and any of the chain guides listed above. Hopefully we can expect to see this technology trickle down to XT soon, especially given the second tier group's trail intention.
The technology behind the concept
Inside the Shadow Plus derailleur is a spring-loaded one-way ratchet gear surrounded by a band-clamp. When the Shadow Plus switch is in the off position, the derailleur reacts like any other with a spring loaded lower pulley cage. With the switch in the ‘on’ position, however, the clamp tightens, engaging the ratchet.
The gear wants to ‘ratchet’ backwards freely, but it must pull against the band-clamp, which acts as a sort of clutch to prevent the pulley cage from moving forward; it can move forward but it takes a considerable amount of force. The end result is an almost fixed lower pulley cage, which prevents the chain from slapping the chainstay or bouncing off the front chainring.
A look inside at the friction mechanism; the switch is turned 'on,' which tightens the band around the central ratchet
In the 'off' position, you can see the cam that tensions the band around the lower ratchet gear
The derailleur is meant to be ridden with the switch in the ‘on’ position all the time, but the ‘off’ setting allows shifting to be initially adjusted or fine-tuned and also makes it easier to remove the rear wheel. The XTR Shadow Plus rear mech will be available from June. UK pricing is still to be confirmed.