XX1, SRAM's dedicated single ring 11-speed drivetrain debuted at Crankworx 2012 and it has proven to be a smart, rider-focused drivetrain solution that has captured the attention of a lot of mountain bikers, despite its high cost. Last summer SRAM announced X01, a slightly less expensive 1 x 11 group. It’s expected that the technology will eventually trickle down to lower price points, allowing it to become attainable for even more riders, but we’ll have to wait a bit longer for that. The February SRAM camp in Queenstown, New Zealand was all about downhill.
Before we delve into the specifics of the downhill specific X01 DH drivetrain, it's worth revisiting the concept behind the SRAM single ring drivetrain philosophy and design. The entire drivetrain has been designed and optimized to create an entirely integrated system that holds the chain better and shifts better than anything previous. It’s not just one or two new parts, but rather an entire system utilizing multiple technologies that work in conjunction to create a better riding experience.
SRAM's 1 x 11 drivetrains have begun to put the nail in the coffin for front derailleurs, a blessing for bike designers and riders alike. Most of the BIKE Magazine staffers were single ring enthusiasts before SRAM came along with XX1, preferring bikes that were taut and reliable with solid chain management and uncluttered cockpits. Now there’s no need to bolt on chain guides as Band-Aids and we can breeze up climbs alongside anyone with a granny ring, keeping up the chat and saving energy for the downs – the reward for big climbs.
So Why Downhill Specific?
Downhill bikes don't have to fill such a wide range of duties as modern trail bikes. They are the UFC fighter of bikes. They just need to be tough, resilient and get down as fast as they can. There's no need for 11 gears on a downhill bike and the consumer market for the beasts is tiny, so why has SRAM bothered to make such a specialized drivetrain?
The idea of a downhill specific drivetrain is actually where the whole XX1 thing began. Ten years ago a prototype drivetrain system was being developed deep in the heart of SRAM's German laboratory. The core principle of this derailleur was that the parallelogram had a straight, horizontal motion rather than a traditional diagonal movement. The idea was to reduce shifting force and isolate the effects of chain pull on shifting. It was designed as a single ring system, which was really only used in downhill at the time. Eventually, the system was mothballed because it just didn’t appear to have viability.
Then four or five years ago, while trying to solve the problems of front derailleurs, the engineers at SRAM decided to look back at this design and see if there was anything that could be learned. The potential wider applications of this system were what interested the engineers so when it was realized that the technology of the scrapped derailleur, in conjunction with other innovations, such as X-Sync narrow-wide tooth profiles, could solve some issues with traditional transmissions. XX1 was born.
Downhill bikes have unique challenges. The longer the travel, the more potential chain growth, thus, downhill bikes can have huge amounts. This growth must be accounted for by the derailleur. Derailleurs with a traditional diagonal parallelogram movement can result in ghost and sloppy shifts as the suspension movement pulls on the chain. The X-Horizon derailleur with its straight horizontal parallelogram movement isolates the force of the chain and suspension travel, meaning shifts are crisp and unaffected.
Because the movement is horizontal only, all chain growth has to be accommodated by the cage of the derailleur. This is why SRAM is offering two cage lengths for the X01 DH derailleur. Some bikes have more chain growth than others so extra care is needed when choosing which length derailleur and cutting the chain to the correct length. Although not all bike manufacturers list the amount of chain growth on their specs, Chris Hilton, SRAM's external drivetrain product manager, hopes that if consumers become aware of the need for proper drivetrain setup, manufacturers will be more likely to list this value. Chris stressed the importance of setting chain length when the suspension is compressed fully and in the largest cog of the cassette. This can be done by unbolting the shock at the forward mount (in most cases) and resting the bike on the ground. Even though it's unlikely to experience full travel in the largest cog, it could happen, and if the chain is too short the derailleur can get ripped off the bike. Thats when bad things start happening.
Less Is More
It has become common for downhill racers to run a funky cluster with fewer gears. Part of this is because if they aren't using the gear, those cogs are just unnecessary passengers. Racers like Gee Atherton, for example, run just seven or eight gears by removing the large cogs from road cassettes. Gee is by no means the only racer on the circuit doing this. Road cassettes were chosen because they offered closer gear ratios. But road cassettes aren’t ideal because sometimes the ratios are too close, forcing racers to shift twice to find the optimum gear. Gear shifts are tiny moments where power can not be efficiently delivered to the rear wheel, resulting in potentially lost time, and races can be decided by hundreds or tenths of a second. Bottom line, road cassettes weren’t designed for downhill racing, X01 DH was.
When we spotted a prototype Blackbox version of the SRAM 7-speed system at the first World Cup downhill round in Fort William in June, 2013, Jon Cancellier, the Blackbox program's man on the ground explained that the integration of Aaron Gwin into the SRAM family from Shimano resulted in some vital feedback which helped inform designers of the direction for gear spacing and ratios.
"We have Gwin on our product now so it has been very interesting working with him because he has experience of other drivetrain systems, knows what he likes and can critically analyze our product. One thing he said was that he enjoyed the ability to shift through two gears on the Shimano product. We asked why and his answer wasn't that he wanted to shift two gears at once, but that he wanted to get into the right gear faster. So we gave him a cassette with more step between the cogs, giving him a real difference between gears. Now when he comes out of a corner and wants to drop the gears and power out, he doesn't have to have the system shift twice to be in the correct gear"
The final production version of the X01 DH cassette is designed with ratios and gear spacing optimized for downhill applications. On the X01 DH 7-speed cassette the range is 10-24 tooth, with two tooth steps on each shift, which can mean less shifting, more pedaling and less time spent decreasing pedal power to allow shifting. Effectively this means less shifting could mean more speed.
Stevie Smith, 2013 World Cup Downhill Overall Champion, explained that for a racer already dealing with a lot of other stimuli and problems to solve on race runs, there were other benefits to shifting less than just power. "I always count the clicks and gears [on my race runs] so this drivetrain makes it easier to count the shifts because double clicking gears makes it harder to count. I start my run in the gear I know I need to get out of the gate with and then count the gears."
Chris Hilton points out that large shifts across several gears at once are less secure than single shifts. "Double or triple shifts are riskier. Single shifts are pretty straightforward but when the chain is crossing a bunch of teeth this is where things can happen. We design shifting to take this in but we want to eliminate risk, especially for racers. Furthermore, the benefits for consumers is shifting less, pedaling more. The benefits for SRAM is better shifting, and a more reliable, secure drivetrain."
Just to confuse the situation SRAM will also be offering the X01 DH drivetrain as a ten-speed option as well. Chris Hilton explained that even though the system was designed for optimized seven-speed downhill use, some people might want more gears so they will offer it. This version will use a specific ten-speed derailleur, shifter and cassette.
Stevie Smith doesn't need all those gears. "There's never a place I need more than seven-speeds. This season I didn't start in the easiest gear once because I like to pedal out of the start, hard", said the champ. Non-world cup riders, however, might appreciate a wider range.
On The Trails
For our mid-winter downhill experience we went to Queenstown, New Zealand. Rising right from the center of this Disneyland-for-adrenalin-pursuits-town, the gondola lifts riders almost straight up to the top of Bob's Peak where an abundance of mountain bike specific trails flow or fall right back down to lake level. Over the course of two days we rattled our fillings loose on steep, dusty, full-commitment, elevator with its cable cut-type trails, as well as more gradient-friendly flowing terrain with a rollercoaster-esque ride. On the third day we shuttled a local downhill trail on the flanks of the Remarkables (a name that flies in the face of typical Kiwi understatedness) which was rocky and very challenging at pace. In the afternoon we were flown to the top of Coronet Peak where we experienced a fun, buff snake of a trail that swooped us 10km down into historical and scenic Skipper's Canyon.
So, what did the drivetrain feel like? It was almost unnoticeable on the first day and a half. And perhaps that's not a bad thing. It just worked, without any grumbles or grinds, just as a drivetrain should. It was on the second afternoon that I made a conscious effort to try and trouble the drivetrain by shifting badly – mid corner, through rock gardens and braking bumps, and under full power. I shifted more than I would normally do so, even opting to pedal out of turns like a championship depended on it, and demanding shifts at inopportune times. The shifting was clean, crisp, and fast, everything is should be, even when trying to mess it up.
The steps between the gears were noticeable. I'd never really thought about how much I double shift while riding downhill bikes, but after experiencing the two-tooth increments of X01 DH it's something I will from now on. One click of the shifter in either direction did provide noticeable changes. It might seem like a subtle improvement but it’s the first cassette made specifically for downhill racing. For riders who want optimum shifting performance and race run advantages, SRAM X01 DH is worth looking into.
The Battlefield Is Set
So why did SRAM go to the lengths to produce a specific drivetrain for the very niche market of downhill? Well, perhaps SRAM's strategy is to demonstrate the wide spread application of its single ring drivetrain system and the core technologies it utilizes. Perhaps it’s to help racers go faster. Perhaps both.
We should expect Shimano to release details of its response to XX1 any time now, and we can only speculate on what it’ll look like. SRAM is very confident that the single ring drivetrain is the right option for mountain bikers when the wide range 11-speed cassette is partnered with a chain ring that is sized according to each rider's needs. SRAM's message is that simplifying the bike is the right thing to do. Shimano, on the other hand, might opt to offer more complex solutions. Which is right? That's for riders to decide, but both SRAM and Shimano will be campaigning hard for what they see as correct.
SRAM have established an integrated system that offers solutions to many shortcomings of the modern drivetrain (chain management, simplicity, fewer levers, adequate gear ranges for variable terrain), creating a paradigm shift that's hard to ignore. Single ring specific drivetrains have been extremely well received by testers and consumers alike, so what happens in the coming months and years will be very interesting to observe.