How can a chainring increase traction? Strictly speaking, traction is a function of the tire and the weight exerted on it. Knowing what we know about the complexities of pedalling up and over technical terrain, balance and how we deliver power to the rear wheel is what we do to maintain that traction. Oversized or eccentric chainrings are not new. The basic idea has been around for over 50 years but was never refined until recently. Proper pedalling dynamics analysis and manufacturing techniques have allowed the design to be refined and applied to the many chainring mounting standards we have today, specifically looking at mountain bikes.
Shimano Biopace is what people who are old enough immediately bring up when you mention oval, or non-round chainrings but these are a slightly different animal. Without getting into too much esoteric engineering jibber-jabber, the bottom line is that the human body, while cycling, is efficient, but inherently cyclical in nature. Good cyclists can spin circles on the road and put down a reasonable amount of power evenly. A quick look at the chart published by Rolloff illustrates this in a sinusoidal graphical format through 360 degrees of rotation:
For each revelation, there are two peaks and two valleys showing points of maximum and minimum torque. This is how the old Biopace systems were developed, relying on the 90 Degree location as the point of maximum torque application available from the cyclist. The whole theory behind the non-circular rings is to try and take advantage of increased power at certain spots in the rotation, and make up for lower power at other ones. I describe the increase in available traction like this: Imagine a newbie cyclist climbing up a steep, loose incline. More often then not they shift into a (very) easy gear and spin like mad. While this makes the load per revolution less for the legs, it removes the one main thing that you must rely on for successful climbing: Balance. Experienced cyclist know that being able to exert more force (to a point) allows you to balance using finer motor skills and your core stability. Spinning too high a cadence does not allow you to use that resistance for balance and causes you to spin out and not be able to correct it because due to basic physics, action-reaction, there is less force on the pedal pushing back on the rider to regain balance. The theory works like this: With round rings, you have to sort of average the power available from the cyclist and size the ring accordingly. Lets take a 32 Tooth ring for example. This is the set-up I use. With the 12% Ovality as One-Up describes, they state that at the maximum ovality (high Point) the ring has the pitch diameter of a 34 Tooth Ring. At the point of minimum ovality, the ring has the pitch diameter of a 30 Tooth ring. This is illustrated (poorly) in the picture below with a standard 32 Tooth Race Face ring overlaid on the Oval ring. It has a larger OD and a smaller OD and the narrowest locations.
One-Up as well as others (Rotor Q rings etc) have the ability to move the ovality wherever you might want, but they have settled on a recommended location of 115 degrees which they state puts the maximum diameter in the start of your power stroke. As this suggests, its 25 degrees below horizontal (90 degrees) looking at the crank arm.
SO back to this balance argument, as you can see, since you are not compromising through an average, you can use an effectively “harder” gear at certain parts of the stroke where you are stronger and an “easier” gear where you are weaker. This effect is that more easily smooth out your pedal stroke with fewer fluctuations in crank speed with applied torque. Torque, power and speed are related through a simple equation:
Torque (Lb-in) = [Power (HP) x 63000]/RPM
- 63000 is a constant in this equation
- 1 HP = 746 watts.Torque is equal to a force acting through a distance, hence pound-inches (imperial) or Newton-meters (metric)
The oval ring has the effect of changing gears twice per revolution but all the while providing a smooth transition between those gears through the outer profile of the oval.
With any “synchronous” mechanical drivetrain, that is, such as a chain drive or cogged belt, not subject to slip, with an oval driver cog (chainring) there would be an uneven speed at the crank for an even speed at the rear wheel. I saw this effect the first few pedal strokes on the pavement when I installed the ring. It felt very weird. For a smooth cadence on flat road at a constant bike speed, the cranks were not smoooooooth. I could feel the speed changes. The thing is, that once you hit a climb and your relatively uneven cadence is exaggerated, the chainring has the opposite effect since it allows you to maintain crank speed where you are weakest in your power stoke (slower) and take advantage of increased available strength and torque generated at the bottom bracket where you are strongest (faster), think pedal masher. We essentially apply a force with our legs at a distance (crank arm length) from the centre of the bottom bracket. This length is maximum with the crank arm at 90 degrees and the applied force from your leg straight down. The 115 degrees offset from One-Up is the adjustment for the true location of maximum power through the biomechanics of the cyclist since we sit at a location above and behind the BB with our legs hinged at our hips. All this adds up to a smoother cadence lessening torque and speed spikes (the real cause of lost traction) and an effect to maintain traction better.
What we have seen is that the chainrings in 1x systems are subject in increased wear compared to 2x or 3x chainrings set-ups where the wear was spread over two or three rings instead of just one. The ring itself for the cinch system from Race Face is offset 2 mm more the the BB than the stock ring. You can see that in the picture below where the two are played flat and the picture is taken at profile.
One up and Race Face chain ring comparison
I have seen that the limiting factor with respect to chainring wear, is not the loaded tooth flank, which normally wears from chain roller interaction, but the side of the tooth wearing on the narrow teeth of the narrow-wide chainrings. The wear is concentrated on the outboard side of the rings. This is from the chain line when operating in the higher (larger) gears on the cassette, the chain is offset from the chainring and the correcting force is towards the drive side of the bike. These teeth wear thin first and cause rough engagement that you can feel in the pedals.
Worn Edge (outboard) of the chainring narrow teeth.
Virtually new edge of the same tooth from above.
These teeth had worn to a razor sharp chisel point. The argument here is that by offsetting the chain line more to the centre of the bike, they will take some of the force and wear effects on these teeth in an attempt to prolong the life of the drivetrain, specifically the chainrings. It seems to be effective, but time will tell.
The Cinch style mounting system is just that, a cinch to deal with. Using an old style BB socket tool, you just remove the lock ring and install a new ring and cinch it back up.
The bottom line here is does the chainring work in the real world by in effect allowing you to maintain rear wheel traction better and clean more loose climbs….The answer here is difficult to formulate objectively, but I can say that as an experienced cyclist, I feel a smoother cadence on steep loose climbs and subjectively it does seem easier to maintain traction. As a test, I did three local climbs that are reasonably challenging: Debeck’s hill climb to Rigs ‘n Zen, Value added climb and full Legacy Climb to Angry Midget. The effect was noticeable since I had done the Debeck’s climb the day before with a regular chainring and it was easier. Also noticed was that tight switchbacks were easier with the same effect. Will this ring make an average climber into an expert? No. What it will do is provide a small increase in overall cycling efficiency on the dirt and maybe allow you to keep it upright in those challenging sections and stay rolling….