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On test: Rotor Ágilis XC2, December 11, 2008
Innovative ideas for the cross country racing crowd
Rotor now offers its intriguing Q-Rings complete with its own Ágilis crankarms for riders seeking a turnkey package. Cyclingnews' technical editor James Huang checks out the light and narrow Ágilis XC2 and finds it to be an very good two-ring choice for cross country racing.
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Rotor follows a different path for its new Ágilis XC2 mountain bike crankset but nevertheless the result is a capable performer. Rather than the currently popular carbon fibre or hollow-forged aluminum construction, Rotor uses new-but-old CNC-machined billet for both the aluminum arms and spider.
Modern external bearings and a large-diameter aluminum spindle go a long way towards making the spindly-looking arms feel reasonably rigid. They're definitely not as stiff as other large-section aluminum or carbon cranks (bigger and/or stronger riders might want to look elsewhere) but they aren't quite the frighteningly flexy deathtraps of yesteryear, either. The drilled-out 'Hollowminium' design helps keep the complete package weight to a competitive 766g.
As is becoming increasingly popular these days, the Ágilis XC2 is a dedicated two-ring crankset intended solely for cross country, and our tester was naturally fitted with Rotor’s own elliptical Q-Rings though it can also be had without. Unlike many other two-ring models though, Rotor opts for a more versatile 40/27T combo instead of the more typical 42/29T or 44T/29, plus a more traditional five-arm 110/74mm chainring spider that offers far more gearing choices to suit the day than four-arm patterns.
Shift performance is very good in spite of the Q-Rings' elliptical shape and big 13T jump though clearly still a step behind the current industry leader, Shimano (then again, so is pretty much everyone). Proper front derailleur positioning is the key to smooth operation, but even so, we got some chain rub on the big ring when in the small-small cross gear.
As for the Q-Rings themselves, they definitely take one or two rides before pedaling feels natural again and their performance benefits are more subtle on the road - they're particularly handy in low cadence situations such as technical trail climbs where constant power delivery is crucial.
The effectively smaller chainring sizes at the dead spots get you back on the gas quicker instead of briefly hanging out in limbo, and the effectively larger chainring size elsewhere means your power stroke nets you a hair more distance for your effort.
The concept admittedly sounds rather hokey but if you haven't pedaled a set for yourself, they're worth a try.
Why just two?
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The obvious benefits to a two-ring crankset are simplified shifting (which is especially handy when your brain is deprived of oxygen during a race) and, to a much lesser degree, slightly lower weight. Rotor goes the next logical step by dramatically reducing the pedal stance width as well - commonly referred to as 'Q-factor'.
Stance width of the Ágilis XC2 is a refreshingly narrow 163mm - a significant 6mm tighter than most modern triples and just about 15mm wider than most road doubles - and unlike what Trek and FSA have done on the new Top Fuel 9.9 SSL, the XC2 fits in a standard 68/73mm shell.
Keep in mind that narrower isn't necessarily better for everyone and potential buyers should also be reminded of the reduced chain stay clearance; we installed our test cranks on a Scott Spark and just barely had enough room for safe operation.
However, for those who feel the latest crop of external-bearing cranksets has made riding a bike feel more like riding a horse - and as long as you have the fitness to handle the 27T low gear - this might be a viable option. Add in a pair of shorter-spindled Crankbrothers Eggbeater 4Ti pedals and you'll almost think you were pedaling your road bike.
But wait, there's more
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Rotor offers the Ágilis as a modular system with one component being one of two external-bearing bottom bracket designs: the standard BB1 which we tested here or the slightly more unusual SABB (Self Aligning Bottom Bracket), both of which are offered with either standard steel or hybrid ceramic cartridge bearings.
Though mostly identical to conventional bottom brackets, SABB adds free-swiveling spherical cartridge bearing mounts in the aluminum cups which supposedly compensate for slight misalignments in the bottom bracket shell such as improper threading or poor facing. At least in theory, the concept makes sense.
Either way, our steel bearing-equipped BB1 unfortunately had a bit of play no matter how we adjusted the Ágilis' unique micro-adjustable spindle length and there was also an appreciable amount of seal drag from the outer dust shields. We eventually swapped out our BB1 for an Enduro unit and got much smoother running and eliminated play as a result.
Yay or nay?
Even with its performance benefits the Rotor Ágilis XC2 is still extremely expensive for what it offers, so weigh your performance goals relative to the costs carefully. Racers looking for a top-end two-ring crankset will place high value in the narrow stance width, competitive weight and versatile five-arm chainring spider.
Unfortunately, we're less impressed with the bottom bracket. Though we've had good luck in the past with a road-going version of the fancier SABB, this standard BB1 was a bit disappointing.
Price: US$399 (Rotor Ágilis XC2 crankarms with semi-integrated spindle);
US$260 (27/40T Q-Rings); ; US$100 (BB1 with steel bearings); US$179 (BB1 with
CeramicSpeed hybrid ceramic bearings)
Weight: 666g (Rotor Ágilis XC2 crankarms, spindle and 27/40T Q-Rings);
100g (BB1 bottom bracket with steel bearings)
Pros: Narrow pedal stance width, competitive weight, elliptical Q-Ring design
an advantage in low cadence situations
Cons:Far too expensive, probably too flexy for bigger/stronger riders,
narrow spacing might not fit all frames, some chainring rub in cross gear combination,
BB1 bottom bracket has too much friction
Cyclingnews rating: 
(Rotor Ágilis XC2 crankset); 
(BB1 bottom bracket)
More information: www.rotorbike.com
Photography
For a thumbnail gallery of these images, click here
Images by James Huang/Cyclingnews.com
- Rotor's Ágilis XC2 crankset is purpose built for cross country racing with a two-ring spider and narrower stance width.
- The Ágilis crankarms are CNC machined both on the outside and inside, effectively making them hollow for lighter weight.
- The 74/110mm five-arm BCD spider allows for a wide range of gearing options.
- The aluminum spindle attaches to the driveside arm with a seven-sided taper. Don't get too excited about the 'CeramicSpeed' etching, though; production units will just say 'BB1'.
- The non-drive arm attachment is adjustable for precise bearing preload. Our sample was mismarked with the 'CeramicSpeed' logo; housed within were standard steel bearings.
