This mention of the torque sensor is an important part of the Direto’s sales pitch. When smart trainers first started to arrive they generally included foil strain gauges similar to the ones on bike power meters. They were small and light but had a habit of coming out of calibration quickly, and no one wants to be sending their turbo back to the factory every few months to get it recalibrated.
These days, while all smart trainers will measure power, most use something called ‘calculated power’, whereby an algorithm works out the power based on electrical current through a coil, but it has to compensate for fluctuations caused by heat.
These can still be pretty accurate, but Elite claims that its solution is superior in terms of accuracy and the lack of a need to recalibrate. Inside the Direto XR is an optical torque sensor (OTS) that measures power directly using a laser to detect tiny amounts of twist at the axle caused by pedalling against a resistance.
Brattle says, ‘The amount of motion is tiny, so it has to be measured very, very accurately. The Drivo used a twin laser system and a twin belt system, which meant you got an incredible level of accuracy – we were sampling about 1,000 times per pedal revolution, which is why we were able to have a 0.5% accuracy. The Direto uses a single laser system, so it doesn’t sample at quite the same rate, but even so it is still independently certified at 1.5% power accuracy.
‘The OTS is heavy, it’s bulky, so it’s not suitable for use on a bike, but for a turbo trainer it’s perfect, and the great advantage is it never needs to be recalibrated.’
Warum hab ich dieses komische "Einkaufsfahrrad mit Gepäckträger" noch nicht! 
