My first motivation for seeking these cranks out really took shape when I started long distance round-island rides again a few weeks ago, after a hiatus of nearly 10 years. In the not-so-old days, I would be able to do 200km in a day without much trouble, even on a heavy Santa Cruz cross-country single-pivot machine complete with heavy wheels, fully loaded panniers and 35 degree heat. Then, after taking a long break from cycling, and coming back to it last August, I surprised myself by not being able to even complete 40km without a considerable amount of pain – all over my body. It was as if I had never cycled before, and had to learn it all over again. In actual fact, that was the case. Even though I was careful to keep in reasonable shape, doing some Thai boxing and gym work each week, I was not prepared for the vigors that long distance, fast road cycling would demand of me.
So it was, during that first round-island ride of 120km, that I realized 2 things – (a) I was going to have to condition my body a lot more, and (b) my knees were starting to hurt a bit. (a) I could do something about, (b) was more insidious. I had no desire to bust my knees and end my cycling life even before it had really (re)begun. Thus began my quest for something that would help me to reduce the knee stress and perhaps, gain a bit of endurance assistance in the process. Ye olde kill-two-birds trick. Enter the Rotor cranks.
In truth, I had already heard about the cranks some time ago, around December of last year. It was at the same time as I was deciding whether to get that, or a pair of Power Cranks. I decided on the latter. I am still using the PC on my training bike (a Colnago Freedom) and a review of them is in the works. However, I did not forget the Rotor cranks and had always wondered exactly how it would be like if I were to combine the effects of both cranks. That is, train on the PC, and ride on the Rotors. At the time, the Rotor cranks were going for over S$1300, and that was really expensive, especially for someone who is not cycling as a profession. Then when I saw the Cyclecraft website advertising the Rotors in August this year for half the original price, my resistance crumbled to bits.
The theory behind the Rotor cranks is simple. There is a dead spot in your pedaling cycle when a crank points dead 12 o’clock, and the other is dead 6 o’clock. Dead spots mean that your legs are not doing anything to push the bike forward when the cranks are at those positions. Thus, if you were doing a 90rpm cadence, this phenomenon will happen 180 times a minute. In a one hour ride, 10800 times. And so on. That’s an awful lot of time and energy wasted simply because most bicycle cranks on the market nowadays are designed in a straight line. And what’s more, this kind of “useless” pushing increases the chances of knee injury and tendonitis.
What the Rotor cranks try to do is to eliminate this dead spot, so that whatever power your legs are generating ALWAYS go towards powering the bike, rather than just pushing the cranks from the vertical 12/6 o’clock positions, and towards the 2 to 5 o’clock section where the bike derives most of its forward momentum. How does Rotor eliminate this dead-spot? By decoupling the spider and the cranks so that both move independently of each other. Originally developed by the Madrid School of Aeronautical Engineering, the idea is to propel the crank mechanically past the 12 o’clock position when the other crank reaches 6 o’clock. The Rotor solution is to offset the rotation of the spider relative to the cranks, and use movable links between the two. This way, on the upstroke, the links pivot inwards and vice versa. This effectively varies the chainring size depending on the position of the cranks during the cycle’s development. I have often wondered why the design team did not just draw up simple off-set cranks rather than go through a complicated system of cam shafts and exocentric axles. This may mean no variation of chainring size, but then again, I am no engineer, and if it took aeronautical geniuses to figure this one out. So who am I to question their design?
The big question for me was: how does the use of the Rotor cranks complement my training on the PCs? When I ride on the PCs, the independently rotating cranks force me to lift them up on the upstroke, ie between 180 degrees and 360 or 0 degrees. The PCs handover point is exactly where the dead spots are, so that overcoming the dead spot still requires one to push the crank over the top where the ratcheting system will finally engage with the cranks again. With the Rotors, I find myself pulling up around 200 degrees to 320 degrees or so. Rotor claims that a small percentage of the downward force is used to propel the upward crank past the last “lame” 50 degrees or so, presumably after the 310 degree point, or even forward of that, ie the dreaded “Dead Zone”. Were one not to pull on the upstroke, a larger part of the downward energy will be used for the Dead Zone. However, the raison detre of the PC is to enable cyclists to learn how to pull on the upstroke, thus saving the energy from the downstroke to forward propel the bike. Therefore, by pulling up to the beginning of the Dead Zone (180 degrees to approximately 320 degrees), all that’s required is a only little force from the downstroke to take the crank completely past the Dead Zone (320 degrees to 10 or 20 degrees). Both legs share the work, the bike goes faster, and both systems complement each other beautifully. Got that? No? Never mind, it’s just theory.
More importantly, does it work in the real world? My first ride out with the Rotors was eventful – and not in a good way. At around the 70km mark, cruising at a comfortable 33kph, I suddenly had the sickening feeling I was pedaling air, and when I looked down, lo and behold, the crank was hanging onto my shoe like a dead leech! It had come off its moorings like the wooden leg off a careless pirate. Some emergency roadside repairs, and subsequent soft pedaling and mollycoddling later, I felt it was safe to put a bit of pressure onto them again. The next day I brought the bike back to Cyclecraft, who realized that besides the non-drive crank having decided to commit hara-kiri, even the drive side crank was coming apart. Strange! They are fixing it as we speak, and I will report on the results of their ministrations and subsequent rides.
What I really liked about the cranks during my maiden voyage (hi Herbie!) was the way they looked from the riding position. The 2 linkage arm points look goofy from the side, but take on a bionic-like appearance from above the top tube, lending the cranks a cool, dangerous vibe. A friend - the same one who laughed his butt off when the crank was dangling from my shoe - likened them to power meter taps. Either way, they made me look more like a badass cyclist than I really am. And that’s good. I was also able to detect the ability to mash the pedals up to a high speed - my Garmin ran out of juice so I did not know how fast exactly - and, wonder of wonders, I did not feel that I was about to expire when I reached terminal velocity. In fact, it felt like I had reserves to go on at that godforsaken speed, a marvel! I did not do so, of course, but I would like to see if I can recreate that feeling on my next ride. Had I been on regular cranks, my lungs would be bursting and my heart rate would be dangerously into the red zone. My next ride would see if I can bear this out, so as they say on radio, stay tuned!
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