The Elite Kura B+ Direct Drive Smart Trainer features the Integrated Optical Torque System (OTS) power meter by Ergomo. This technology is exclusive to Elite trainers & is certified to be accurate to within less than 1% making it the most accurate power measuring system available to the public. All Kuras are tested & calibrated before shipping using an Lorenz industrial torque meter. Once calibrated an occasional software-based recalibration is all thats required, no sending your trainer back for recalibration. Resistance is controlled by a super powerful, smooth & quiet fluid resistance unit. The faster you go the harder it gets, just use your gears as you would when out riding. The 4.5kg internal flywheel is geared up for high RPMs, generating a far smoother feel than conventional flywheels. Connection to your devices is easy. The Kura B+ will connect to Android or i OS devices with both ANT+ & Bluetooth Smart. An internal generator powers the sensors & transmitters, meaning the Kura does not require mains power & can be used anywhere. When not in use, it folds down for easy portage & storage Comes with a 9/10/11 speed Shimano compatible freehub. Compatible with 130 & 135 Q/R rear ends, as well as 142 x 12 thru-axles