Oval-chainring-curious riders who still harbor doubts about the concept should give Race Face's new Cinch Oval chainring a try. It's effective and it requires little or no adaptation time. The caveat is that you'll need a Race Face crankset to make that happen.
You can order a Cinch Oval Ring in 28, 30, 32 or 34-tooth options, and flipping the direct-mount sprocket will center its chain line for Boost or "Super Boost Plus" hub spacing (standard DH-width hubs). Race Face Cinch Oval direct-mount chainrings are crafted from 7075-alloy aluminum, retail for $81.99 CAD or $64.99 USD, and are compatible with all current Race Face Cinch cranksets.
Cinch Oval Ring Details: • Fits all Race Face direct-mount cranks • 10% ovality • 112.5-degree timing • Black anodized, 7075-alloy aluminum • Compatible with 10, 11 and 12-speed • Narrow-wide tooth profile • Sizes: 28, 30, 32, 34-tooth • Reversible to fit 148mm Boost or 157mm Super Boost chain lines • Weight: 72g (32t) • MSRP: $64.99 USD • Contact: Race Face
The rings feature an “Ovality” of 10 percent. This means the ring diameter varies from 95 to 105 percent of the equivalent round ring.—Race Face PR
The Cinch crankarm self-extracts with an 8mm Allen key. A Race Face bottom bracket tool unscrews the lock ring that retains the direct-mount chainring.
Installing the Cinch oval chainring is simple: Use an 8-millimeter Allen wrench to remove the self-extracting drive-side crank arm; Use a Race Face bottom-bracket-cup spline tool to unscrew the retaining nut at the base of the existing chainring; Switch the existing sprocket with your new oval chainring (make sure to line up the "Crankarm" sign) and then screw the parts back together. The entire job takes ten minutes, tops.
Race Face direct-mount chainrings can be indexed at any one of sixteen spline locations, which might encourage riders to experiment with different clocking points. I'd be careful to try the stock setting first before you start messing around. Each position will advance or retard the timing by 22.5 degrees, and that represents an extreme change. I can feel the difference between 10 and 12 percent.
Race Face took their time to figure out how much "ovality" was too much and then diligently worked with different clocking angles to ascertain where the major axis of the chainring should be located to maximize its effect. Cinch Oval Rings have a ten percent difference between their major and minor axes, and are "clocked" at 112.5 degrees. What this means to the rider is that there is just enough ovality in the chainring to provide more consistent torque around the entire crank circle without creating abrupt speed changes at the pedal. It does this by increasing the leverage moment where the legs are ineffective (more torque with less effort) and reversing that equation as the crank arms rotate into their power zone.
Chainring timing: The clocking angle is an average figure that takes into consideration the geometry created by the rider's leg, the frame's seat tube angle, and where the "dead spot" occurs in the crank circle. When you get that right, power delivery feels more natural from the rider's perspective, and torque output to the rear wheel is smoother and more constant. The improvement is most noticeable during high power/lower RPM events, like steep climbs.
Smoother power stroke: Whether you agree or not, the reality of round chainrings is that pedaling action creates irregular power pulses at the rear wheel which encourages wheel-spin. A good oval chainring minimizes that pulsing and delivers power in a more controllable way that maximizes grip - especially when traction is iffy. If you do break traction while climbing, an oval ring makes it easier to pedal through the wheel-spin, instead of stalling.
Cinch sprockets are "dished," so they can be reversed to fit Boost or Super Boost chain lines.
Riding impressions: I have been using a 30-tooth Cinch Oval Ring on a Pivot Mach 5.5, driving a Shimano 11 x 46, 11-speed cassette. That's a bit of a stump puller gear for some riders, but the hills I have been using the bike for are steep and technical. The terrain was familiar, which gave me the chance to compare round rings and other oval types in an apples-to-apples review.
I was surprised by how seamless the transition from round to oval was. I jump back and forth between the two, because test bikes always come with round rings. and that is what occupies most of my riding time. I expect that switching to an oval chainring of the same number of teeth will lower my maximum cadence slightly and require me to shift more often, but that was not the case this time. My cadence remained steady and I literally forgot that I was riding an oval ring until I was reminded that something had changed after I cleared a particularly difficult, very lumpy rock garden climb with relative ease.
There is less of a "peak torque" sensation - the five or ten degrees of pain-spike you get from round chainrings when your legs are feeling spent. The Race Face chainring made it easier and less painful to keep the pedals circling during those moments.
Race Face's narrow-wide tooth profile shows little wear, in spite of some grimy wet conditions.
Race Face machines the tooth profiles of its Cinch Oval Rings in the neo-classic, narrow-wide configuration that virtually guarantees that the chain will stay put as long as you pair it with a clutch-type rear derailleur. If you do want to use a top guide or similar, they say that most guides will work fine with a ten-percent oval. I have found that to be true, but I did not use a guide and have yet to lose a chain.
Other concerns with oval rings are noise due to the chain meshing with the sprocket teeth at constantly varying angles - and that some oval chainrings create unwanted movement of the rear derailleur's chain take-up arm. My test chainring was a bit noisy for about a week. Not bothersome, but considering how quiet SRAM Eagle is, it was noticeable. The Cinch chainring has broken in now and, without showing much wear, is running quietly enough that I never notice it.
Theoretically, the same number of teeth are engaged at any point in the rotation of an oval sprocket, so there should be no change in chain length as it spins. In reality, there is always some machining or mathematical error on an oval sprocket that causes the rear derailleur to move slightly. Race Face's design is the best so far, with so little movement that it does not even come close to engaging the derailleur's clutch, which is the only real concern.
Race Face's Cinch Oval Ring is one of the better options available. I think its modest, ten-percent ovality is perfect for mainstream riders and modern riding styles. It is not so aggressive that it will require you to adapt your pedaling style, yet the benefits are tangible in all respects. I'd recommend one to any oval-curious rider who owns a Race Face crankset.—RC