Want to baffle people with your amazing speed on a mountain bike? Take a look at the Gruber Assist, a unique retrofit for bicycles that adds a fully-functional electric motor on the sly.
Instead of the typical setup requiring you to install the motor on a visible area (which leaves the bike looking a little clunky), the kit has been arranged in tubular form. Both the 22-inch long motor and the drive assembly are integrated inside the bike's frame, making the whole upgrade completely discreet.
The Gruber Assist uses a 200-watt electric motor, delivering 100 watts of power (equivalent to about 60 pedals per minute) to the rear wheel to assist your pedaling. A full charge should net you 45 minutes of no-pedal action, although it can last up to 90 minutes if you work your legs out a bit. It can make room into most standard bike frames with a seat tube diameter of 31.6 mm. A small saddlebag that you can attach to the seat's frame holds the rechargeable battery pack, while the switch controls are mounted right on the handlebar.
If you feel like a small boost can help you during your bike rides, nothing gets it much more stealthily than the Gruber Assist. The downside is the kit costs $2,399, a serious step-up in pricing compared to less-clandestine motor retrofitting you can get for your bicycle elsewhere.