Germany’s Berner Bikes makes carbon fiber upgrade parts and accessories, carbon road and ‘cross frames and other bits. These replacement derailleur cages caught our eye despite having been available for a while now.

Available for SRAM Red, Shimano Dura-Ace mechanical and Di2, and Campagnolo Super Record, the carbon fiber cages use oversized 13t and 15t jockey wheels with slick bearings to reduce friction. You can order them as a hop up kit on its own, or as a complete derailleur. You can even send in your own and have them do the conversion for you. They even offer a Ceramic Speed bearing upgrade if you’ve got money burning a hole in your pocket.

The switch adds about 19g to the part, but they say it’s good for almost a six watt savings and that numerous pros are running them in the peloton. The Shimano Dura-Ace part’s shown above, click through for more pics and pricing…


The outer face of the Shimano part above, a converted SRAM Red derailleur below.


Prices range from €269 up to €659 depending on model and whether you’re ordering parts or a complete derailleur.


  1. Let me see if I understand this. These ADD weight, add cost of $300 to $750 and are claimed to save more watts than a rear derailleur actually consumes, right? P.T. Barnum was too conservative.

  2. @gerald t., do you not understand what Bike Rumor is all about? It’s about interesting bikes, parts, etc. Don’t want to read about these, don’t click on it. I skip over all sorts of articles that don’t interest me and read the ones that do. It’s the beauty of the Internet! Then again, I don’t get to be as pissed off all the time as you.

  3. Dave: Larger pulleys on bigger bearings ought to roll more smoothly. Snake oil or not, there are riders after marginal gains where they can get them, like riding with Alberto Contador on the Port de Balès. Ahem.

  4. @AlanM – +1…
    @Dave B, gerald t…as best I can tell, no one is holding a gun to your head to either click on any links, or to purchase any products you see on BR…

  5. For 99.% of the cycling world, something like this simple is not necessary. very cool, very expensive, but the cost vs gains are so far out there. The concept is simple. By making the pulley larger, the chain can turn the pulley easier by overcoming the friction in the bearing much easier. This is the exact opposite idea that makes Kreitler small-drum rollers so hard to spin. The bearings are the same but increasing or decreasing the diameter by which you are trying to spin them makes them easier or harder to spin. the carbon cage has no benefit over the stock aluminum one unless they just needed to make something out of carbon.

  6. Aerospace engineer here:

    The pulleys are going around slower. Power is torque times rotational velocity, so slower pulleys consume less energy.

    Larger diameter pulleys require less force to overcome the torque of the bearing. Power is also force multiplied by time, so less force over the same time is less energy.

    Finally the chain’s link will swivel over a smaller angle joining and leaving a bigger pulley. Less chain articulation will mean lower frictional losses and less energy.

  7. According to Friction Facts, the actual savings is about 1.8 watts over the Dura Ace 9000 11/11. The savings comes from 3 sources: Lower friction bearings, larger, slower spinning cogs, and, quite importantly, the spring tension applied to the chain is lower.

    The price is 380 EUR. For people spending $8K on their bikes, this seems like a completely reasonable expense. If 10 similar enhancements were available, it would cost about 4K to add 18 watts, which is a serious advantage. You’d probably get better performance if you bought a $4K bike and did the 18 watts of enhancements.

  8. I have one of these on a WyndyMilla Massive Attack SL. Very high quality bit of workmanship on the cage (carbon/alloy) and the bearisngs are very good. The first ride with it is very noticeable – akin to sticking on ovalised chain-rings for the first time. Expensive yes, much looks and feels great. A couple of watts there, a couple more from RotorRings.. Super stiff frame.. all starts to add up (assuming you FTP has stalled out!).

What do you think?