Rotor follows a different path with its new Ágilis XC2 mountain bike crankset but the result is a capable performer nonetheless. Rather than the currently popular carbon fibre or hollow-forged aluminium construction, Rotor uses new-but-old CNC-machined billet for both the aluminium arms and spider.
Modern external bearings and a large-diameter aluminium spindle go a long way towards making the spindly-looking arms feel reasonably rigid. They’re definitely not as stiff as other large-section aluminium 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.
Oval rings are worth a try
As is becoming increasingly popular these days, the Ágilis XC2 is a dedicated two-ring crankset intended solely for cross-country and our test set 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 versatile 40/27T combo instead of the more typical 42/29T or 44T/29, as well as a more traditional five-arm 110/74mm chainring spider that offers more gearing choices 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 pedalling feels natural again and their performance benefits are more subtle on the road, but they’re 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 sounds rather hokey but if you haven’t pedalled a set for yourself, they’re worth a try.
Three's a crowd
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 slightly lighter 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 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 chainstay 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're pedalling your road bike.
Good idea ... in theory
Rotor offers the Ágilis as a modular system with 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-swivelling spherical cartridge bearing mounts in the aluminium 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’s unique micro-adjustable spindle length and there was also an appreciable amount of seal drag from the outer dust shields. We eventually swapped our BB1 for an Enduro unit and got much smoother running and eliminated play as a result.
Yea 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.