, perhaps, but when Race Face developed the 16-tooth splined interface for its Turbine Cinch crankset, it answered the prayers of Marcin Golek. Golek is the founder of Absolute Black, and a staunch believer in elliptical-shaped chainrings as a superior method to deliver power to the ground. Marcin discovered through testing his un-round chainrings that differences in leg length, and the rider's position over the crankset require slightly different "timing" in order to ensure that the major axis of the chainring was in position when the rider was producing peak torque.
The concept is not new. Rotor, the world's most famous oval chainring maker, offers a number of timing options for exactly those reasons. Turns out that the 16-tooth spline interface of the Race Face Cinch crankset offers three useful timing positions for the Absolute Black chainring: "Neutral" (Marcin's preselected position that he believes will work for just about everyone), and either 22.5 degrees ahead or behind that point. The drive-side quick release feature of the Race Face crankset means that the chainring can be re-timed in less than15 minutes, without removing the bottom bracket axle from the frame or breaking the chain.
Absolute Black is headquartered in the UK, where their design, marketing and testing takes place. The chainrings are CNC-machined from 7075-alloy aluminum in Poland and then finished in the UK. Chain retention of their narrow-wide tooth profile is warrantied for 12 months and you can get them with 30, 32, or 34 teeth, in green or black anodized colorways. Our 32-tooth oval ring weighed 60 grams and carries an MSRP of $66 USD. Absolute Black also makes a full range of oval chainrings for SRAM direct mount and the most popular four-bolt cranksets.Absolute Black
Oval Sprocket Theory
For those who are not up to speed on oval chainrings, the concept is not a re-introduction of Shimano's 1980s-circa BioPace. The major axis of the oval chainring is timed to arrive as the leg develops peak power, while the smaller, minor axis is timed to arrive near the "dead-stroke" to increase the mechanical advantage of the crankset when the legs provide very little power. Theoretically, the result is more constant torque is generated around the crank circle. For mountain bikers, that means more climbing traction and the ability to maintain momentum in situations that require high power output. Worth noting is that oval and a round chainrings with equal numbers of teeth will propel the bike forward at the same speed at a given rpm, so only power delivery and leverage rates around the crank's circle are affected. On the same subject, switching to an oval chainring causes little or no change in chain length as it rotates, so the rear derailleur cage doesn't rock wildly back and forth with every pedal stroke.
Installing Absolute Black's chainring to the Cinch crankset was surprisingly easy. The Race Face drive-side crank pops off the end of its 30mm shaft with an eight millimeter Allen wrench. A threaded retention ring fixes the spider (or direct-mount chainring) to the crankarm, which fits a readily available splined bottom bracket cup remover (Park Tool BBT-20
). To index the oval Absolute Black chainring, you line up a dot machined near the spline with the crankarm. The entire process takes about as long as it does to read this article - which encouraged me to try all three timing positions with the oval ring and also compare it with the stock, 32-tooth Race Face ring on the same trails.
We used the Commencal Meta V4 to test the chainring. Its 72-degree seat tube angle is slacker than most trailbikes, which should have favored retarding the sprocket one click counter-clockwise, and initially that seemed best, with a very gradual transition from the larger to the smaller axis of the sprocket. Advancing it one click clockwise had the opposite and negative effect - causing the leg to speed up dramatically as the knee reached full extension. Climbing a steep grade with a smooth surface revealed that retarding the sprocket one click felt better because that was the position that caused the sprocket to perform and feel much like a round chainring - a strong acceleration, followed by a brief lag. If there was any doubt, both the round and the oval ring left the familiar broken line scratch marks on the dirt. When I returned the sprocket to the middle position, the broken lines created by each power stroke on the pedals were smoother and closer together - an indication that I was making torque where my legs had previously been coasting around the crank circle.
I decided on the middle position even though there was a distinct pulsing, created by the legs speeding up as the oval sprocket turned through its smaller axis - a sensation that made it awkward to spin the cranks at my 90 rpm cruising pace. Two, maybe three rides later, the pulsing sensation was gone and I could spin the cranks as well as with the round ring. I normally ride a 30 tooth chainring on a 27.5-inch-wheel bike, so the 32-tooth ring put some heat into my legs on the steeps, but that helped to clarify where I was making up ground and where I may have been slower with the oval rings.
There was no doubt that I was consistently faster when climbing technical terrain, because I could keep the cranks turning in familiar situations where I had flailed on the pedals using the round ring. I lost some momentum on trails where the grade changed constantly, because I found that I was shifting gears more often with the oval sprocket. That said, I could hang in a taller gear for a longer duration than I could with the round ring if I was willing to slow my cadence slightly and gut it out. Pinkbike's Take:
|To end on a practical note, Absolute Black's take on oval chainrings provides its most palpable benefits during those moments when you are pushing the pedals in earnest, especially against a lot of resistance, like plowing through sand or mud, working up a steep grade with variable surfaces, or getting up stepped rocks and roots. Pitted against a round ring, it pedals about the same over smooth, flat terrain and when topping rolling climbs out of the saddle. Speaking to the timing aspect of the Race Face/Absolute Black marriage, I ultimately didn't need it with the Commencal's 72-degree seat angle, but in retrospect, I had the option to experiment and make an educated decision. Plus, retarding the timing allowed me to get used to the sensation of the oval sprocket by moderating its effects, and then move up later to the optimal timing. Initially, I was worried that the oval ring would work my knees more than I wanted. After switching back to the round ring for the remainder of the Commencal review, however, I was reminded of the constant pulsing (which we have all learned to live with) and ultimately, the oval sprocket proved easier on the knees. If you own Race Face Cinch cranks, and you have 66 bucks to burn, Absolute Black's oval chainring would be well worth a try. - RC|