People often ask about doing this, and, particularly if you have a favourite bike that will respond well to a suitable conversion, then you may wish to do this.
Please note however that the authors can only recommend ‘proper’ kits that have been thoroughly developed as a complete and complementary product by a reputable dealer (Motor, Battery, Charger and Controller together) and either self-fitted by someone who is fully competent for the task, or by a local bike shop.
See Richard Peace’s helpful buyers-guide for a good round up, and there are moderately strong mid-drive kits to convert your own bike, e.g Bafang or Tongsheng motor powered kits from such as the well regarded Woosh bikes or the Dillinger kit.
Note: The author has fitted a £600 ish Woosh bikes bikes supplied Tongsheng 48V 250W TSDZ2 torque sensing mid drive kit to a friend’s MTB.
The fitting was quite straightforward, and the motor offers plenty of go and a good range, however it has not been super reliable, either refusing to ‘kick in’ and go from a start, or occasionally cutting out on the ride, needing a reboot and pause before restarting , maybe suggesting an issue with the Torque sensing arrangement.
That being the case it may be better to stick with the crude but effective Bafang stalwart.
The author recommends the excellent lightweight Cytronex front hub driven system. This features a more on demand ‘power-boost’ facility, rather than full time power, and will be well suited to converting more nimble commuting and leisure cycles, including the road bike tested by e-bike tips here , and also by the excellent A to B magazine
The author has recently fitted 3 Cytronex kits to friend’s hybrid and touring bikes, and impressions are very good – it looks and feels very well built, is easy enough to fit, the power delivery seems very smooth, albeit, as expected, significantly less than a mid drive system.