I would like to convert my current bicycle into an E-bike. While there are many conversion kits available and plenty of sites with tips on this, none of them quite meet my needs, or they fail to explain exactly why certain choices have been made. I am looking for an answer that provides insight into exactly what matters in this type of conversion.

Current situation:

I commute to work on my bike 2 times a week, which is 75Km (45 miles) round trip. My bike is a 2010 aluminium cyclocross bike with 700 x28 road tires and standard canti brakes, otherwise Shimano Ultegra parts. Front fork is carbon. The terrain is flat, with about 5% gravel roads. Location is Northern Europe, so plenty of rain. I normally ride this distance with an average speed of 26 - 28 Km/hour (16 - 17.5 M/h), depending on wind and traffic.

Budget for converting is not very high (few hundred $, certainly below 800$), but I am willing to spend quite a lot of time on sourcing the right parts and am pretty confident in my DIY skills, including building wheels and batteries if need be. Getting another bike to commute on is not an option.

Reason for converting

Main reason for wanting to go electric is reducing travel time. The two commutes a week per bike are a part of my exercise schedule, so reducing tiredness or getting to work easier/without sweating are not important. Ideally I would like to convert and still get a reasonable amount of exercise, only get to work faster (35-40 Km/h)/(22-25 M/h). This means that I still put in the equal amount of energy that I currently do (meaning I can reach 28Km/h on my own) and the motor supplies the extra energy required to go 35 Km/h. In case of a removable battery, charging at work would be an option, but an effective range of 75Km to be able to make the round trip without charging would definitely be very nice.

Decisions to make

Motor type and placement: What I understand so far is that within my budget, a direct drive 48v hub motor would be best. I do not really care about their added weight or drag when not active. For weight distribution, a front wheel motor would probably be nice, but I am not sure how well this goes along with my carbon front fork, and if it even fits (over locknut distance). When looking on e-bike motor sites, almost all of the motors seem to be very high power (500W/1000W). I really doubt whether I need this amount of power, when all I need is a little support to get from 28 Km/h to 35 Km/h. I do not expect the bike to pull me along without myself delivering most of the effort. Would something like 200W not be enough?

Choosing a controller:Controller should be compatible with the motor and battery, and not be limited in speed to at least 50Km/h. Regenerative braking would be nice, mounting to a drop-handlebar is nice, but I expect to have to make some custom solution for this anyway.

Choosing/making a battery: Obviously, some form of lithium ion battery is best for performance/weight. But what are other (budget friendly) alternatives? Is a sealed lead battery really such a bad idea? How much costs savings can I expect when building my own battery out of Lithium cells? and how feasible is it to import them from China? Battery mounting will probably be some form of custom rack.

Getting second hand parts: What are my options regarding second hand parts, what is the life expectancy of an e-bike system (excluding battery, of course)? Is getting a second hand donor bike for electric parts a viable option (they are often found quite cheap here, when the battery has died they are sold for 300$) It is of course difficult to find exactly the parts (mostly motor type) you need in a second hand bike.


Is there anyone with experience with such an conversion who can provide some insight into what really matters to make a fast bike go even faster with a custom DIY solution, without me having to empty my bank account?

  • 1
    Please look up the local laws in your area. Many places limit the speed of electric bicycles. In my area it's 32 km/h. The European Union Definition states a maximum of 25 km/h. If there's a lot of hills, you may still reduce your travel time as you'll be able to go faster up the hills, but if it's mostly flats you might not save time. You might be able to go a little above the max speed without drawing attention. Talk to other cyclists in your area to see how these laws are enforced, if at all.
    – Kibbee
    Mar 11, 2015 at 12:57
  • 1
    You are not going to convert and still get the same exercise. Work the motor does is work you don't do.
    – paparazzo
    Mar 11, 2015 at 13:21
  • @Kibbee, I am aware of the legal limits, but not very concerned. It is not uncommon for road cyclists to go 35Km/h, which happens to be my desired speed. This would not draw any unwanted attention.
    – biker12
    Mar 11, 2015 at 13:55
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    "I would like to convert and still get the same exercise, only get to work faster." You are not going to get both of those. I am not getting the time management thing. You state you want the exercise. You are going to get less exercise to save 40 minutes.
    – paparazzo
    Mar 11, 2015 at 13:58
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    Also consider that what you're looking for might be difficult. The power required to overcome drag varies relative to the cube of the velocity. Take a look at this calculator. It takes 64 watts to travel at 20 km/h, 172 watts to travel at 30 km/h and 373 watts to travel at 40 km/h. It requires 108 extra watts to go from 20 to 30, but 199 extra watts to get from 30 to 40. Traveling at an average of 35 km/h is going to be quite difficult over that distance, even with a motor. average 40 km/h is approaching TdF speeds.
    – Kibbee
    Mar 11, 2015 at 14:39

2 Answers 2


It is possible. For 250W motor, without any limit, I can go 20 kph on a 8% grade hill. But that will burn your battery and motor, so please be careful about the discharging current limit if you are planning to DIY deep into the software/hardware. Most Chinese brand can be reprogrammed easily with a usb cable to the controller. On flat, I can go 36kph, which is 8 kph less than the rated speed of the unloaded motor.

Most 250W motor can withstand 350W for a short time, but mind you, while going uphill in warm weather (~24oC), it can burn your motor easily if you do not assist the motor and let it run at ridiculously low RPM (less than 10 kph is bad for motor).

Battery: DO NOT go backwards to Lead-Acid Battery. It has ridiculously long charging time, shorter cycle life, and 4xheavier than LiPO4 (2.5 kg as opposed to 10kg, and you do not want 10kg of Lead and Acid with you around). So again, NEVER think about using LeadAcid battery for your sake. The money you save does not worth the hassle you have to go through, even if you are broke and homeless...

Motor: consider gear Hub motor, as they are lighter. You have cantilever brake and that's another reason to get your bike as light as possible. You can get a good Geared hub motor for £250 which weighs 2.1-2.4 kg.

Controller and Wiring: get some waterproof wiring/plugs and controller so that you do not have to worry about cycling in the rain

P.S In all honesty, I would sell the carbon fork to get better components for e-bike, then buy a cheap alloy fork (maybe 300g heavier, but with better e-bike components, you can save 2-3 kg of weight in the end)


I live in the southern most part of Nashville, TN (quite hilly with a major hill between my community and the rest of Nashville). I ran into @Blam's point exactly and have been considering investigating this new technology.


The weight is the lowest comparable to other options (battery variable). TOP SPEED US: 20 mph, EU: 25 km/h BRAKE TYPE Rim brake and regenerative braking (downhill and back-pedal) WEIGHT 5.9 kg / 13 lbs DROPOUT 120 mm (single speed), 135 mm (single speed and multi-speed)

I haven't ridden one yet but it may be worth investigating.

  • 1
    That is a 3 speed internal hub. Probably not a good conversion for a cyclocross Ultelgra.
    – paparazzo
    Mar 12, 2015 at 20:24

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