MTB Jockey Wheels get warn down. In addition to guiding the often filthy chain through the rear derailleur, they also have to contend with grass, wire, branches, leaves and all sorts of other stuff can get caught up in an average off-road ride. Despite all this, the jockey wheels keep on turning. When it comes to replacing warn jockey wheels, Merlin stock direct replacements as well as aftermarket items from Tacx, BBB and Hope.