Bringing together three trends in cycling – power meters, ovalized chainrings and twin-ring mountain bike cranksets – Rotor and SRM will begin selling their 3D+ Mountain Bike Double* in June.
The upcoming crankset combines an SRM power meter with Rotor's 3D+ mountain bike cranks and will send data wirelessly to any ANT+ compatible head unit from the likes of Garmin, Timex and SRAM. It'll be priced at $2,499 – about $500 less than Rotor/SRM road power meters. Rotor don't yet have a final weight, but say it'll be available 1 June.
The 3D+ MTB Double is SRM's 36th power meter crankset. They also make power meter spiders for cranks from Shimano, Campagnolo, Specialized, Cannondale, FSA, SRAM, Clavicula HRM and Tune. In total, they offer 22 road models, 12 mountain options (including a downhill version with a Shimano Saint crank and a single-ring model based on SRAM X0), one BMX offering and one track set. Riders who already have Rotor 3D+ or other compatible cranks can just buy the spider, send it in to SRM and have it retrofitted and calibrated.
Power to the pedal... and to the ANT+ computer on your handlebar
The 3D+ is named for three weight-saving drillings; two run the length of the aluminium crank arm and the third is bored in perpendicularly. The crank arms come in 170, 172.5 and 175mm lengths with a 30mm axle, but they're also compatible with threaded and BB92 bottom brackets. Featuring a 120/80 bolt pattern, the 3D+ can be used with Rotor's oval Q-Rings (in 42/28, 40/27 or 38/26-tooth configurations) or SRAM/Race Face round rings (39/26 or 42/28t).
Many mountain bikers are sold on the concept of double cranksets, and most racers can at least see the benefit of a power meter. But why oval rings? “Personally, I think that they have the most benefit on mountain bikes as you get better traction as well as more power,” Rotor's US general manger Kervin Quinones told BikeRadar. “True, you can’t really measure traction, but with a smoother power curve there’s no hiccup, and constant tension on the chain helps in the loose and technical stuff.”
A few pros have found success with Rotor rings, either through official affiliation or otherwise. On dirt, Burry Stander and Christoph Sauser won the Cape Epic on Rotor rings last month. Marianne Vos won the Cyclocross World Championships on them, and former world champ Kristin Armstrong just won the Tour of the Gila using Q-Rings on both her road and time trial bikes. Quinones said Cervélo-Barracuda sprinter Tyler Farrar has been using them as well. Brits may have noticed that Team Sky’s Bradley Wiggins won the Tour of Romandie with oval rings, but those were from Rotor’s competitor, O-Symmetric.
* The new power meter crankset has two names. Depending on which company you speak to, it's either the Rotor 3D+ Mountain Bike Double SRM or the SRM MTB PowerMeter Rotor 3D+ Double.