Many cyclocross bikes route the derailleur cables along the top tube to get them out of the way of mud flung off the wheels and away from places the rider might grab during portaging. Since the front derailleur cable now leads down the seat tube and all road shifter compatible front derailleurs are bottom pull, the frame builder must incorporate some sort of cable pull reversing pulley on the back of the seat tube below the height of the front derailleur. This is unfortunate, because that pulley is now situated in one of the muddiest nooks of a cyclocross bike. A problem….that clearly needs some obsessive German tinkering!
Enter German company Speen. They manufacture tiny little doodads that they call Umlenker in a plethora of (very) minor variations to fit just about every front road derailleur currently made. The Umlenker bolts onto the cable fixing threads of the front derailleur, and then it presents a repositioned cable fixing point to accept a cable from above. I believe that Speen first started making these when elite XC mtn bikers started hotrodding their ultra light bikes with double rings and Dura Ace front derailleurs (i.e., before 2×10 drivetrains became a stock option from SRAM and Shimano). In the case of mtn bikes and road front derailleurs, the designated Umlenker for that situation also modifies the cable pull geometry to correctly mesh with the mtn shifter. On a cyclocross bike, the Umlenker is lighter and less of a mud collector than a pulley, though the cable run now sits a little outboard of the seat tube (see pix). Also, the Umlenker lacks a cable groove in clamping area, so tightening the fixing bolt is a little harsh on the cable itself.
You can buy these things direct from the Speen website, and they ship via international post, so the cost is reasonable. I bought a few of these recently, and the one for a customer’s titanium disc 26”-wheeled randonneur bike meshed perfect with the 5700 double front derailleur. I also had success with a Campy Centaur setup. Unfortunately, I inadvertently ordered an Umlenker for the wrong generation of SRAM Force derailleur, so I can’t test that situation out yet. The Umlenker is just a teensy, tiny bit off from fitting my later-gen Force derailleur, but judging by how subtle the differences are between any of the Umlenker models, I suspect that a little “off” may as well be a mile.
Byron is currently testing another CX bike that came with an Umlenker installed. In direct contrast with my experiences, that one shifts like ass. The pull ratio seems like it might be off, rendering the trim positions ineffective. Since I didn’t order or install that Umlenker and none of the Umlenkers have any identifying marks, I wonder if perhaps it is not the right model Umlenker for the shifter or derailleur.
It is worth mentioning here that Shimano is on the eve of delivering CX70 and CX50 front derailleurs, both of which will be available in top-pull options, thereby negating the need for an Umlenker or pulley for Shimano users (assuming they have 5700/6700/7900-gen shifters). Whether or not this will be a trend that SRAM follows is anyone’s guess, so the next time I get a cyclocross bike made, I will be planning on running it with an Umlenker for my SRAM drivetrain.