The Gruber Assist kit is a very cool electrical motor retrofit for standard bicycles which gives pedal assist power from an invisible drive train. The clever bit is to embed the 22 inch long motor and drive assembly into the frame by making it tubular, so instead of having to replace wheels, you just have to replace a seat pillar (video). The kit offers 200W of power, weighs a trifling 900 g and comes with a saddlebag housed NiMH battery (or LiION option) which will give you up to 1.5 hours worth of assistance depending on pedalling speeds.
All you need is a bike frame with a seat tube diameter of 31.6mm (which caters for most standard mountain style bikes on the market as far as we can tell). The downside? You’re going to have to stump up a hefty €1,790.00 (£1,597.00/$2,399.00) for the complete NiMH version. But for those with an expensive bike living in the city, this may be one of the best ways to give yourself electric power without attracting even more attention from would-be thieves.
The auxiliary drive, with a length of almost 22 cm and 200 watts of power, is permanently connected torque-proof with the drive shaft of the foot pedal through a bevel gear unit; gear changing is still possible. At an optimal pedal frequency of approx. 60 pedal revolutions per minute, the bicycle drive provides the rear wheel with up to 100 watts. The entire drive unit (motor, transmission, electronic control) weighs no more than 900 g. The NiMH high-performance battery (approx. 1700g), which fits into a conventional saddlebag, provides you with motor-assisted cycling lasting for 45 minutes up to 1.5 hours, depending on how hard you pedal.