Synchronizing Chainrings… Now.
The idea that the chain retention technology found on X-SYNC™ rings could actually work to keep a chain on a chainring seemed impossible to the marketplace when the technology was first introduced. That’s what makes the genesis of a bold idea like X-SYNC so intriguing. Although the idea behind X-SYNC chainrings seemed simple, making it work, and work well, was far from easy.
To get the full development story and learn how this mountain bike technology was adapted for the road, we had a roundtable discussion with SRAM mountain bike X-SYNC chainring designer Markus Reiter and road X-SYNC chainring designer Bryn Johnson.
Where did the idea come from for the X-SYNC chainring?
Markus: In the 90's SACHS (the brand SRAM acquired in 1997) made a drivetrain system called the 3x7 (a forerunner to SRAM's current DD3™ systems) that utilized a single front chainring driving a seven speed cassette mounted on a three-speed internally geared rear hub. Back then it was even used by some DH-pros, with a chain guide of course. After SRAM acquired Truvativ in 2005, the chainring in that system was designed with special teeth to hold onto the chain better. The problem with these thin rings was that the chain retention still didn’t meet our expectations, and that’s how the idea of X-SYNC came up. We wanted to see how far we could push the chain-retention abilities of the teeth and threw everything we had at it. There were 12 years of cassette design experience and 1.5 years of chainring design behind that effort.
SRAM Direct Mount X-SYNC MTB chainring.
Are there any key differences between SRAM MTB and SRAM Road X-SYNC rings?
Bryn: Yes, many. Some key characteristics are that the mud-shedding grooves in the tooth roots of MTB and cyclocross X-SYNC chainrings were eliminated in favor of maximizing stiffness on the larger road rings. The chainline was also moved further inboard to minimize cross-chaining to the larger rear cogs, reducing noise and increasing drivetrain efficiency in the low gears. Tooth forms and profiles were carved away in appropriate places to maximize long term performance, yielding an optimized X-SYNC asymmetric tooth shape with a smoothed profile to minimize running noise.
Markus: Another key difference is that SRAM road 1x rings are made to be used only with a road chain to ensure optimal performance and balanced long-term wear.
Bryn Johnson at work on X-SYNC road chaninrings in SLO.
What challenges did you run into designing the road X-SYNC chainrings?
Bryn: First off, although it used an existing technological element, the road application is significantly different from the previously released, primarily off-road CX and MTB versions.
For example, wear life. Road bikes rapidly pile up much higher mileage counts than off-road bikes. In fact, we were very surprised at the relatively low mileage professional cyclocross racers put on their CX bikes in a season.
Couple with this the fact that the road rider would now be spending 100% of their ride time in the one chainring, versus about 70% large ring / 30% small ring on a road double, and again high mileage is a challenge. Maintaining performance characteristics with anticipated high mileage and associated wear was a challenge as well.
With respect to chain retention, road riding will not typically introduce the same levels of terrain-induced chain movement as off road riding. In fact, Cyclocross is the absolute worst case for this challenge. Skinny rigid bikes with no suspension and small tires make cyclocross chain retention far more challenging than MTB applications. Also, road riding will not generally be subjected to the same environmental challenges as off-road – namely mud and debris build-up on the drivetrain.
Lastly, road race sprinters can generate some of the highest power and torque applied to a bicycle drivetrain. A derailed chain in these sprint situations can be disastrous. So, engineering in pro sprinter level chain retention was also a challenge.
It should also be noted that regarding chain retention, SRAM’s 1X road drivetrains are designed as integrated systems including the X-SYNC chainring, X-Horizon™ rear derailleur with Roller Bearing Clutch™, SRAM chain, and SRAM cassette. Without these other components, performance is severely compromised. The X-SYNC chainring is good, but the integrated system is stellar.
How did you balance the need for quiet operation and efficiency?
Bryn: It’s probably fair to say that there is a solid connection between a drivetrain’s running noise and efficiency.
Markus: But it all depends where the noise comes from. A noisy jockey wheel doesn’t necessarily slow you down, but can make a racket.
Bryn: True. It is clear however, that there is no time that drivetrain running noise is more obvious than when riding on a slow road climb on a quiet road. This leads to the perception that cross-chaining to the larger cogs, when you are climbing and exerting big energy, is inefficient. In fact, running noise in the smallest cogs is typically louder and commonly less efficient, however, road and wind noise produced when riding at speeds typical of smaller cogs far exceed that coming from the drivetrain, leading to the perception that the small cogs are quiet and efficient.
So the challenge becomes optimizing chainline and tooth shape. Chainline (the lateral position of the chainring on the bike in relation to the cassette) has to be optimized, to balance cross-chaining, noise, and efficiency on a macro level. Optimizing tooth shapes, profiles and offsets to engage the chain quickly, smoothly and quietly, minimizes lateral chain movement and therefore noise and efficiency on a micro level.
What about hitting the strength and stiffness requirements?
Bryn: This is more a case of how single 1x chainrings perform compared to a traditional road double (2x) set-up. On a 2x crankset, the inner chainring creates a bridging, stiffening member that is very much a contributor to the overall strength of the system. Removing the inner chainring creates the optimization challenge of maintaining strength and stiffness while keeping the 1x chainring weight at a minimum.
As with most aspects of bicycle design, it is easy to make something light, but not so easy to make it stiff and strong, as well as light. At SRAM we take pride in having what we believe to be the most stringent requirements for front drivetrain strength, stiffness, and resistance to the types of huge pedaling forces that can be imparted by world-class athletes. The fact is that many imitation products cannot even meet SRAM’s minimum requirements in these areas.
X-SYNC chainrings sizes 38-46t feature mud evacuation grooves at the base of each tooth. 48-54t X-SYNC rings eliminate these grooves to improve chainring stiffness.
After the SRAM rings were released many similar “narrow-wide” chainrings came to market. What makes SRAM X-SYNC rings different beyond the stiffness and strength aspects you mentioned?
Bryn: Performance on chainrings has always been about fine details and X-SYNC 1x is no exception to this rule. Most of the imitators have simply taken their standard chainring tooth shapes and added a “wide strip” to every second tooth. In contrast, a close inspection of any SRAM X-Sync chainring tooth will reveal that they are different in every facet when compared to SRAM shifting chainrings. These geometric differences, when combined with the other pieces of the SRAM drivetrain, the chain and X-Horizon rear derailleur, deliver SRAM X-SYNC’s superior chain retention, low running noise, and high efficiency.
Additionally, and extremely important, is the chainring’s wear tolerance, or maintenance of performance characteristics, during normal drivetrain wear and tear. The geometry of SRAM road X-SYNC chainring teeth is designed to sustain high levels of chain retention performance throughout its lifetime.
Why did SRAM develop X-SYNC road chainrings in San Luis Obispo rather than in Germany where the original X-SYNC rings were designed?
Bryn: SLO is our road front drivetrain expertise base, plus, in-house at SLO we have the ability to rapidly complete all of our own prototyping, inspection, analysis and laboratory testing which greatly accelerates the development process. The world-renowned road riding and year-round favorable riding temperatures in the area help, too! Plus we have lots of really rocky fire roads and trails that are perfect for testing chain retention. Ultimately, however, product field validation testing is performed by a global test team, which includes professional level road, triathlon and cyclocross racers.
For information on how to find the right gearing for your SRAM 1x drivetrain click here for a setup guide.