What are the advantages of a building an electric bike from a kit vs. prebuilt

I have tried two ebikes before and to be perfectly honest - they are very poor uphill - almost any hill. The motors are too weak in my view and here the laws won't allow you to ride a bicycle with a motor that has more than 200 watts of power without a motorbikes license (Australia - except QLD). The best motorised bikes I think are the petrol ones such as the common Moped. Much more power and you hardly have to provide a down pedal to push it along.

I am coming at this from the perspective of converting a bike I have, in my case my Bacchetta Giro 20 ATT recumbent bike [link to my blog documenting my build experience] but before I decided to go down this path I did look at off the shelf e-bikes and for me I couldn't find a reasonably specified [in terms of bicycle components] e-bike at a reasonable or comparable price so as I had the existing bike I decided to go the conversion path.

Based on my experience which was more involved because of the recumbent, if I was considering doing this again I would look for a suitable source bike [either second hand or new with a 68 mm bottom bracket and space to take a frame battery] and then consider installing a Bafang BBS02 mid-drive [750 watts] with a 48V battery. Installation is generally pretty straight forward and really quite quick, the kit is not to badly priced and the motor by all reports is a good performer.

With regards to your Craiglist bike, I wouldn't be considering a 36V battery to power a 750 watt motor as being an ideal option. From what I understand 48V is a better option with the more powerful motor.

Endless-Sphere whilst pretty full-on is worth a visit to get some idea about conversion options.

From personal experience (Xtracycle's EdgeRunner), if you go DIY or pre-selected kit, make sure you budget for companion upgrades:

• Battery, motor, controller will add significant weight to the bicycle. Factor in cargo as well (you'd be surprised how much MORE you're likely to haul around if the effort is lower).

• The motor drive/pedal assist will guarantee higher velocities (more like 20+mph vs 10-15mph). Both will contribute to a much harsher environment for your drive train, braking surfaces, and wheels.

My upgrade path in order of conservative importance:

• A reliable and trust-worthy brake system is essential. Cable-actuated calipers with a correctly sized rotor (for total ride weight) on a quality disc hub is the bare minimum.
• If within budget, get hydraulic brakes.
• Front drive-train including shifter, crankset and chainrings, and derailleur: with battery assist, you spend a lot of time in high gear - make sure it can safely handle the torque you will be dishing out.
• Rear drive-train - shifter, cassette and derailleur: same reasons as above
• Rear brake system - if not upgraded at the same time, this is where I would place your dollars last.

My recommendation is that if you are good with understanding how electrical motors and circuits differ, thats where you should begin. Stepper motors servo motors are what you are after and amperes is your power output. Watts is how long your power lasts until recharge is needed.

First, check your local laws. As others have mentionend, in some countries (EU), maximum power for an electric bike is 250W. Go beyond that and the vehicle will be considered a moped and will need license, insurance and and license plates. Your local laws might also require an assist-only option for your bike to be considered an e-bike. That means usually a pedal sensor, and those can be difficult to install especially with exotic or outdated bottom brackets.

Selecting a kit is not necessarily easy. If you're going to front mounted motor, check that brake type is compatible (disc or v-brake) with the kit and that fork spacing is suitable. E-bike kit should come with brake levers with a cut-off switch so the motor stops pushing immediately when braking (problem with some e-bikes).

Kits can be had cheap, but installing them takes time, effort and experience with bike mechanics. If you got all three, go for it. If you need to get up and running quickly, an entry-level e-bike is probably better option.