Electric Bike Motor Kits – What You Need to Know

Who wouldn’t want a bike motor when sitting at the bottom of a large hill?  Recumbent bikes are notoriously poor climbers.  Yes I know some are better than others, but over all having an electric hub motor on your bike can “erase” the pain of climbing the long steep hills.  But how do you know what you need and where to buy it?  These are the questions I’ve been researching now for several months.  Months you say?  Yes, months because finding a quality solution isn’t as easy as it should be.  Yes you can buy a kit from a number of online retailers, but how do you know it’s going to work and how do you know it will be any good?

Here is what you need to know about Bike Motor Kits

Please excuse the rambling thought processes here as I have a lot to write and little time to write and edit it.

Electric Bike Motors come in a couple of flavors.  You have hub motors which encase the motor inside the hub of the wheel, and you have inline motors which attach to the frame and need to be integrated into your chain system and bottom bracket. The advantage to the first is ease of installation, the downside is they are unable to take advantage of your bicycles gearing for more efficient climbing.  Hub motors are generally quieter in operation than a bike motor which attaches to your chain drive.  The chain drive as mentioned is a bit more noisy but can take full advantage of your bicycle gearing for climbing.

For my purposes with the design of my bike frame the hub motor is the only option.  Hub motors come in two style – Direct Drive and Geared.  A direct drive system is basically large copper wires wound tightly with magnets to create a motor. They are heavier than geared motors and they will not freewheel. So if you have no battery power your bike motor will drag against your pedaling effort.  I don’t like the idea of fighting the resistance of the motor.  However direct drive motors are very powerful and usually less expensive.  A typical direct drive bike motor will weigh 15-20lbs plus the weight of the rim, spokes, and tires.  A geared hub motor is about half that weight and doesn’t look so out of place.  In fact some geared hub motors can be “hidden” underneat disc brake hubs so your bike won’t look much different.

In the United States the legal limit for electric bikes is 20mph.  It’s my understanding that 750 watts of power driven from a 36 volt battery will be the maximum legal kit combination for the USA.  You can use 48 volts of power to most kits and the speed will exceed the legal limit.  In the UK and most of Europe I believe the speed limit is closer to 15mph, but they use kmh and I didn’t bother to check the conversion because I won’t be riding there any time soon!

So what should a typical person who just wants a little help climbing the hills buy?  In my opinion a geared hub motor.   The direct drive motors do not have moving parts like the geared motors, but in my opinion unless you want an electric moped and the additional weight, which will change the handling characteristics of your bicycle stick with geared.  But it really depends on you, your goals and your bike.  A good geared motor (more on what good means later) should last plenty long as long as you do not feed it too much power which can  burn up the gears.

Here is where it starts to get frustrating.  Electric bike motors are not made in the United States, or at least any that I could find.  They are all coming out of China, so there really isn’t much way to know what is good and what is not good unless you find an experienced dealer who is willing to stand behind these Chinese bike motors with a warranty and service program.  And for me that is a problem, because I don’t want to throw money at a no name Chinese product only to have it fail.  This is an even bigger issue with Battery Technology which also comes out of China.

I can not recommend any specific brand but BMC, Bafang, Ezee, 9 Continent, etc. are names you will see most often.  You can purchase complete kits from Bionx which is a Canadian company, but they do not make a geared hub motor.  And the Bionx kit doesn’t play well with those who want to mix and match parts – batteries, controllers, etc.  The Bionx system is proprietary… you wear out the battery then you replace it with one of theirs.  There are pluses and minuses to this arrangement, but I don’t have any plans to get into them here.  I should note that Trek Bicycles has an agreement to use Bionx systems on their electric bikes.

For my purposes I’ll be going with a front drive kit.  The rear drive kits are usually not dishable (This means the axles may not center in your back drop outs).  So what do you do then?  How do you adjust the brakes on your bike if you have V-Brakes?  Dishable wheels are important to bicycles if you want them to perform correctly.  You’ll also not have enough space to use much more than a 5 sproket freewheel, so you lose a lot of useful gears for cycling purposes.  If you only plan to ride electric this is not such a big issue.  But on a front wheel dish is not important as there is no sproket to consider.

Further considerations for electric bike motors are the rims and spokes.  Because these wheels can generate a lot of torque you’ll need to use a heavy duty double walled rim (550g is about the lightest you can go) with heavy duty 12-13 gauge stainless steel spokes).  Some of the better heavy duty double butted spokes from DT Swiss, Phil Wood, Sapim will work as well.  But here is the kicker – you won’t find name brand spokes or rims from any of the Chinese companies.  You find whatever brand they happen to be using… and the tolerances and spec’s are pretty crappy for bike components.  You roll the dice and could end up with a wheel that isn’t very true and spokes that are not properly tensioned.  Some distributors like e-Bike Kit will rebuild their kits in the United States which helps with these quality control issues.  This is a big deal if you are using V-Brakes as an untrue wheel is a huge problem.

Should you want to actually stop your electric bike motor while riding (I think most of us do), you need to make sure the braking options (disc or v-brake) will work with your bike.  This can be tricky with some Recumbent Bike handlebars which are not ideal for the brake cut off handles that ship with most kits.  Again these brake handles are of much lower quality than most of you will expect.  But when you are going down the road you should have an option to tap the brakes to disconnect the motor.  It’s a safety problem if you do not have a way to cut off the brakes – your motor will be running while you are trying to brake!  This is a recipe for crashing.

Mounting your wheel to you bike is another potential problem.  Many ebike motor hubs are machined with axles that are larger than the drop outs on your bicycle.  You may have to file your drop outs a bit to get the axles to fit.  I do not like the idea of filing rear bike drop outs – you mess up and you ruin the frame.  Another reason to use a front wheel drive system.  You ruin a fork drop out and you can easily (and for much less than a frame) replace the fork.

If your bike has “Lawyer Lips” (The notches on the sides of a lot of front forks which prevent the wheel from falling out if the quick release is not properly secured) are a problem for electric bike wheels, because you need a firmly secured axle or the wheel will spin out and damage both your drop outs and the wiring which comes out of the wheels.  Free spinning an electric motor because it is not properly secure is both a safety problem and a financial problem.  You do not want to damage those wires or your hub motor is toast!  So you’ll need to make sure you get “c-washers” (Axel Spacer Nuts) so your can torque down your wheel.  But how much torque?  Good question, as I have not seen a specification for torque yet, because I have not selected a kit although I’m leaning towards a custom built Bafang or Ezee hub on a Sun Rim with Sapim spokes.

Controllers and Batteries.  You could write article after article on Battery Technology.  I recommend you head over to Endless Sphere Forms or one of the other forms and do some reading.  Lithium batteries are lightweight and last a long time while delivering constant voltage at low weights, but they are also very expensive and they come in so many flavors.  You want a lightweight battery that lasts and performs over the long haul.  The most well known manufacture that I’ve found is “Ping Battery”.  These are custom built “Duct Tape” batteries and will cost as much as the wheel kits.  You’ll also need a controller to make sure the battery is not destroyed by pulling too much current, and to make sure the wheel gets the right amount of juice to propel you forward.  Again there are really no name brands here… you are on your own, so it’s best to find a dealer who has a good track record and talk with them.

This is not easy putting together an electric bicycle solution for your needs.  With each turn you find you need to know something else and it’s hard to get those answers.  For example:  You’ll probably want to use a torque arm, but which one?  And how many washers ill I need?  In what order do I assemble the washers?  What kind of electrical connectors should I use and will my battery connectors match the hub controller?  How long will the wires need to be, what gauge and how will I secure them to my bike?  How water proof are these wires and connectors?  What happens if I get water inside the hub wheel.

It just goes on and on, and it’s frustrating.  I wish the the United States of America would FIX ITSELF… start making things here again, take pride in what is being made.  I shouldn’t have to look to china to put something as simple as an electric motor on my bicycle, but that is the state of the Country today.  It is what it is.

Sorry for the rambling, I’m sure this is incomplete, but my goal here isn’t to offer answers to every problem with electrifying your bicycle, rather to open your eyes to some of the potential pitfalls should you choose to do so on your own bike.