Rotor Crank System

By Coach Fred Matheny

Pedaling a bike can be pure elegance. Watch a pro smoothly turn rapid circles while he climbs or time trials. it’s poetry in motion.

Or is it? Biomechanical studies show that there’s a pronounced “dead” spot when one crankarm is at the bottom of the stroke and the other leg is trying to push the opposite crank over the top and down, where maximum power can be exerted.

Garage tinkerers and big companies alike have tried to solve the problem. Shimano even foisted the infamous elliptical “Biopace” chainrings on us in the 1980s. They didn’t work.

What makes the Rotor different? The rings are round and a cam system changes the angle between the two crankarms. When one crank is at dead bottom center, the other has already moved past 12 o”clock and started down. In theory, this eliminates the dead spot and increases the amount of time you can spend in a more favorable position to generate power.

I was curious about the Rotor partly because I like time trials and it promises to increase wattage at lactate threshold — the very essence of races against the clock. In Europe, a number of triathletes and mountain bikers are successfully riding Rotorized bikes in their TT-like events.

Weighty Concerns

I talked Uncle Al into doing the installation at his shop, Cascade Bicycles in Montrose, CO. For an experienced mechanic like him, the Rotor was relatively easy to install. He slipped it into a Specialized E5 frame using liberal applications of Loc-Tite.

The first thing you notice — even before riding — is the Rotor’s weight. This pup is heavy. At 2.7 pounds it’s one pound more than a Dura-Ace crankset. You can feel it when you heft the bike.

The Rotor also turned stiffly when rotated by hand, due to the cam mechanism.  The movement improved with use.

Re-Learning to Ride

The biggest shock is how this crank feels while riding. At first, it was nearly impossible for me to pedal up the street from my house. It felt like I was falling forward at the top of the stroke. Cornering was spooky, too. When you put the outside pedal down and weight it, the other crankarm is already starting its downward flight.

I became somewhat accustomed to the altered pedal motion but never really adapted. My knees got sore during three hours of riding, causing me to stop the test and return the cranks. But a number of European riders have stuck with it and apparently feel “normal.” I didn’t get the sense that would happen for me after 30 years of pedaling conventional cranks.

Assuming you rode the Rotor enough for it to feel right, does its cam action increase power output and performance?

The jury is definitely out. Several studies show increases in wattage and reductions in lactate production of around 15%, along with a 5% drop in heart rate. These improvements would translate to a significant performance increase — on the order of 3 minutes over a 60-minute event. But we need to be wary of these studies. They were commissioned by Rotor, and the applicability of lab results to real-world performance is always suspect

Bottom line: The Rotor crank is a clever way to address inefficiencies in the pedal stroke. it’s a promising idea. But the current unit is heavy, costly and requires lengthy adaptation. More R&D seems necessary, and we need more proof that its weird pedaling action actually improves performance.

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Coach Fred Matheny is an RBR co-founder who has four decades of road cycling and coaching experience. He has written 14 eBooks and eArticles on cycling training, available in RBR’s eBookstore at Coach Fred Matheny, including the classic Complete Book of Road Bike Training, which includes 4 eBooks comprising 250 pages of timeless, detailed advice and training plans. The Complete Book is one of the many perks of an RBR Premium Membership. Click to read Fred’s full bio.