Editors Note: Dogman is a well respected guru of the DIY electric bike community who has ridden 10′s of thousands of miles on his frugally built hub powered electric bikes.
First question is, what is a commuters electric bike? Short answer is, It gets you from point A to point B. Typically a trip that is done often, like home to work or school and back. For this article, I will be discussing electric bikes that do not greatly exceed the guidelines of 750watts maximum, and 20 mph maximum. For many commuters, these limits are enough power and speed to get the job done.
Why build an electric bike? Why not just buy something ready to ride? Usually the choice to build rather than buy ready made has to do with needing more range, or more power than offered on some ready to ride electric bikes. But if your needs are small and your distance short, go buy an inexpensive ready to go electric bike:
How do you choose the bike to ride? At this point, it’s time to analyze your needs. First, how far is your daily ride? If your daily ride is 3 miles or less, go do it on just about anything. Unicycle, Wacky bike 10 feet tall, tiny bike for a five year old, whatever. A mile there and a mile back is too short a ride to get very uncomfortable on anything. For me, at about 3 miles one way I start to notice if I’m riding a bike that has a bad seat, or an uncomfortable angle on the handlebars. But likely I can still tolerate a few flaws in the bike’s fit to my body for 6-8 miles one way. Once you will ride the bike as much as ten miles one way on your commute, it’s time to get serious about your comfort. This may mean suspension, or recumbent seats, or simply choosing the right size frame for your body in whatever type of bike you like best.
A few types of bikes tend to make better longer distance commuters than others. The most common recommendation is to choose a 26” mountain bike frame made from steel. Strong can be more important than light weight since you now have a motor to help haul the weight. A good quality cromoly steel bike can be very strong. Generally they have enough space in the frame to carry a battery in the frame, rather than on a rear rack.
For long distance rides, you want to be able to carry stuff, so look for mounts to attach a rear rack, and stronger frames. A nice size frame triangle in the front of the frame can be a big help. Carrying the battery in the triangle gives you better bike handling. Better handling improves comfort for the long haul. With the battery in the frame, more cargo can be carried in panniers or on a rack.
Low quality bikes can be less comfortable than higher quality bikes. In some cases the frame may be sized for teens rather than full size adults.
The bike may simply have a poor saddle, or handlebars that look cool, but are not comfortable for longer rides. Brakes can be very important, and cheap bikes tend to have less effective brakes than higher priced bikes. But even the cheap v brakes can be pretty effective if adjusted right. You don’t have to have disk brakes, but some cheap caliper type rim brakes are really useless. If you get rim brakes, at least be sure they are the V brake type.
Here are a few pictures of low quality bikes I made into commuter electric bikes.
My first attempt was a trike:
It was never intended to go much farther than 10 miles. It worked, but the trike had some serious problems. It got hard to steer and turn at higher speeds, and the motor I put on it allowed speeds up to 30 mph. So you had to choose between slow and unsafe. Slow had little appeal when going farther than 10
Next try was a cheap full suspension bike:
Bought used, it was falling apart by the time I put 500 miles on it. The frame actually cracked. The suspension on it worked, but not very well. Built for a young teen, I began replacing handlebars with taller ones, and using very long seatposts.
So I thought, I’ll buy a new cheap bike:
I picked out a type known as a comfort bike. To my surprise, the suspension on this new bike was a lot worse than the other cheap bike. It bottomed out on tiny bumps. It was an unbelievably poorly made bike. Also the small gear on the front crank made pedaling along with the motor impossible. You need a high gear to pedal along at 25+ mph. This bike, like the trike, was geared for 15 mph max. The problem was not that it was a comfort bike, the problem was that it was a really poorly made one.
On to the next try, the same full suspension bike as the one that broke the frame, but this time the bike had little wear on it:
I put a few more modifications on it by then, including better bracing on the rear rack, and a big chain ring on the cranks. By now, the cheap bike gets new crank, new seat and seatpost, and new taller handlebars. This one worked out pretty good, and got ridden over 2000 miles. The frame never cracked, but it softened up and got floppy. If you used the rear brakes the frame would bend, and you’d get no brakes. It just got rode too hard for the quality of the bikes cheap frame.
So now my advice is to use a good strong frame. It may be a cheap but strong beach cruiser, or a bike built for hard trail riding, or a bike built for carrying cargo. But the common thing is you want a frame that will not crack, or get soft and floppy. The electric bike may weigh 35 pounds more once you add a hubmotor and enough battery for long distance rides. The most commonly used type is a MTB with only front suspension:
The battery can be carried in the front triangle, and a rear hub motor installed in back as in the pictured editor’s bike.
You may have noticed that all those early bikes had a front motor. The reason for this is because none of those frames have room to carry the battery in the frame. If you put the battery high up on a rear rack, the only way the bike will handle ok is if you have the motor weight on the front to balance things out. Front hub motors can be ok on bikes with steel forks, but if the bike has alloy suspension forks, a front motor can be dangerous unless installed by an expert.
The easiest path to a good commuter for most people remains an MTB with front shocks and a large frame triangle, combined with a rear hub motor.
My current commuter bike is based on a much higher quality bike frame. Still using the front hub since it is used only on pavement:
This bike has some pretty good shocks on it, making riding really long distances much more comfortable. It has a high enough gear to pedal along at 25 mph, and for the first time, the frame actually fits my body. The battery is a 48v 15 ah lifepo4 carried in the metal box on the rear rack. The rack is reinforced with two braces that diagonal back to the frame. It is quite capable of carrying 50 pounds on the rack and in the panniers, but handling suffers when loaded that heavy, so speeds are best limited to 20 mph when fully loaded. The motor is a direct drive hub. Because of the alloy forks, it has torque arms on both sides of the axle:
I have ridden this bike about 6000 miles. The frame is still in great shape despite carrying huge loads, but I have worn out a rear wheel and a set of forks. The choice of a strong frame that fit my height made all the difference in the world. It turned out so much better than previous attempts with cheap bikes.
Now it’s time to choose the motor for your commuter electric bike. What motor you choose, what type, and how much power you need will depend on the your needs. I have always been a big fan of choosing the right tool for the job. If the job is easy, anything will do the task. If the job is difficult, then you need to have a more expensive more durable, and more powerfull tool.
The easy commute is less than 5 miles one way and has no long or steep hills. Since the distance is short, comfort and speed matter less. 20 mph travel will get you to your destination in much less than half an hour. Since there are no steep hills, a lower powered motor will get you there. 400 watts will usually get an ordinary bike cruising on flat ground at 20 mph. And 400 watts will get you up a moderately steep hill. Moderate hills are less than 5% grade. Pedaling a bit can lower that to 200-300w. Since the wattage is low and the ride is short, a less expensive and smaller battery can be used. Even your great grand fathers battery technology, lead acid, can be good enough. But a typical choice is a 10 ah lithium battery.
Any electric bike motor can do the easy commute, but the most economical choice is often a small 250-350w planetary gear motor. The economy is mostly in the less expensive battery. Why spend money on more power you simply don’t need?
The moderate commute may be longer distance, and have long and or steep hills. I call a hill steep if it has a grade of 5 to 10%. If the commute is still flat, then 400 watts is still plenty of power for 20 mph travel, and the need is mostly just for a bigger capacity battery. But generally for a commute of 10 miles or longer, more power is desired. Even if you have no big hills, wind can slow you down, and a 30 minuite ride can turn into a 50 minuite ride leaving you late to work or class. So it’s a good idea to have enough power to ride 20 mph into wind, and 15 mph up 5% grade hills. 700-1000 watts does the trick. Many states in the USA limit speed of electric bikes to 20 mph, and power to 750 watts. The battery suitable to that level of wattage and distance will have to be bigger. 15 amp hours and 20 amp hours size batteries are popular for range in the 15-25 miles ballpark. My commuters have all been built for a moderate commute.
The motor for a moderate commute is often a direct drive motor with 500-1000 watts of power (read our Crystalyte or 9c Review). Also suitable are larger planetary gear motors with 400 watts or more. (read our BMC review) But the direct drive motors tend to handle the longest rides better, since they shed excess heat quicker.
The difficult commute has much longer distance or really tough steeper than 10% grade hills or both. Often an electric bike built for the difficult commute goes beyond the legal power and speed limits for riding on the street in the USA. But if the problem is steep hills, then a bike can be built that sticks to the legal speed limit in your area, and nobody needs to know how much power the bike has. As long as the bike is not illegally fast, it’s not likely to be noticed by police. The battery for a difficult commute often needs to be the very most powerful and lightweight type, because large amp draw controllers can kill ordinary e-bike batteries. Use of RC hobby lithium batteries for their huge discharge rates is common.
The RC lipo battery is also very small and light, which helps if the commute will take a lot of battery to have enough range. If the commute is difficult because it’s 20 miles long or more, then more speed can be the solution. Keep in mind, in most places in the USA, a really fast electric bike is an illegal homemade unlicensed uninsured motorcycle. But the rules vary from state to state, and in some places the e-bike is classified as a moped. This usually means a valid drivers license is required, but more speed and power may be legal. Where you are allowed to ride may change too, you might not be allowed on a bike path with a “moped”.
There is no typical motor for the difficult commute, but direct drive hub motors are often used because they can tolerate running at higher wattage without breaking gears. Really big powerful hub motors are appearing in the marketplace, along with custom frames built to carry large batteries. Custom fabricated mid-drive bikes are the cutting edge of high performance.
Check your local state, county, and city laws. Check using official government web sites. Don’t go by what people who sell the kits say. Your e-biking is governed by the local motor vehicle statutes. Off road, and not on public bike trails, you can ride a high powered e bike. Anywhere an off road motorcycle is legal, your homemade motorcycle is legal.
Electric bike motors come in three categories. mid drive, friction drive, and hub motors. Mid drive has a motor mounted to the frame driving the wheel by a chain.
Mid drive systems have some advantages. (see our story on mid drives) The big one is that the motors chain drives the crank of the bike, then the power goes through the gears to drive the wheel. This allows the rider to select low gears to climb a hill. This can get a bike up a hill with less watts, but the price may be slow travel up the hill. The big disadvantage of chain drive can be a rider who selects too fast a gear while climbing a hill. This can cause battery damage or motor overheating. Other problems can be issues with the gears, such as poor sprocket alignment, difficulty installing the motor mounts on some frames, and they may be noisy. The power of the motor is limited to what the bikes chain and gears can tolerate, but a 1000w or less power level is not generally a problem. There is a subcategory of mid drive where the motor chain drives the wheel from a separate gear on the left side of the bike. In that case, the gearing is fixed. That approach is often seen on “frankenbike” type electric bikes that are completely made from dumpster scavenged parts.
Friction drive motors drive the wheel by pressing a roller against the tire. They were once common, but in recent years they have become rare. A few people have fabricated their own improved friction drives that are the lightest possible e bike motors. They make a great motor for those who want to motorize a very light bike, and feel that a 10-15 pound hub motor is too heavy. Disadvantages can be tire wear, or slippage in wet conditions. (see our story on friction drives)
Hub motors have other advantages. They are fairly weather resistant, easy to install, and much quieter than a mid drive. If it matters to you, a hub motor can be selected that will keep the bike looking very much like it does not have a motor installed. Hub motors come in two basic types, planetary gear motors and direct drive motors. Hub motors exert force on the dropouts of the bike frame or forks when the power is turned on. The use of torque control devices is highly advised. Most reputable vendors of hub motors also sell torque arms. Sometimes, custom torque arms have to be made by the user. This is usually because the rear dropouts of bike frames are less standardized than front forks. One vendor has just introduced a universal rear motor torque arm.
Planetary gear motors have internal reduction gears that let the motor spin faster than the rim. This gives the motor a wider power band that improves low speed performance, such as starting up from a stop sign. The gear motor also has an internal freewheel that allows much easier coasting and pedaling when the motor power is off. That gets very important if you run out of battery power, or want to pedal with the motor off to extend range. The smaller, low wattage gear motors are lighter than most direct drive motors. That light weight, plus the freewheeling ability make 250-350w power gear motors a very good choice for the easy commute. Larger gear motors with 400-800w power work well for the moderate commute. Disadvantages are an audible but not loud gear noise, and slower cool down if the motor is overheated. More mechanical parts means it’s possible for them to break, but most gear motors today have more durable gears than in the past. The internal freewheel can be broken, but generally last many years in normal commuting use. (see our geared motor vs direct drive ride report)
Direct drive motors are the simplest of all. They have one moving part, and two bearings on the axle. That’s it. If the motor is not overheated, it can have a nearly infinite service life. Bearings might need replacement, but likely the motor will greatly outlast the rim it’s laced on. Generally the quietest of all e-bike motors, but leaving the stop sign the motor may grunt, or make humming noises as the motor gets to speed. Once at cruising speed, direct drive motors are usually silent or nearly silent. Since there is no freewheel in a direct drive motor, regenerative braking is possible. Direct drive hub motors can radiate excess heat better than gear motors, so they can be a good choice for hot climates or long uphill rides where overheating can be a problem. Power levels for direct drive motor kits tend to be in the 500-1000w range. The motors usually can tolerate 1500w very well, and some riders will run even more power, and simply shorten the duration of the ride to avoid overheating. So the direct drive motor is often chosen for hot rod off road e-bikes. Disadvantages are less performance at slow speeds leaving a stop sign when used at 750w, a narrower range of efficient running speeds, and bit more weight and size. The choice of the right motor winding gets important, and the right winding varies quite a bit depending on the wattage that is chosen, the rim size and the kind of use. Picking the right motor for the difficult commute is tricky, but fortunately the typical e-bike direct drive motor kit comes with a motor winding that is suitable for nearly any moderate commute. When steep hills are involved, direct drive motors can overheat easily if the hill is too steep and the rider allows the motor to lug down to less than 15 mph for very long. Typically, the standard kit motor can climb a 5% grade fast enough to have no problems, even if the hill is two miles long.
Once you have chosen the motor and controller, you have set your power level. Now you can finally choose your battery. Here is where you need to get comfy with some technical stuff. So for starters some definitions.
Amps is how the flow of current is measured, it’s like measuring the flow of water, such as how far open a valve is.
Amp hours, is how the capacity of a battery is measured. It’s like how many gallons of water flowed.
Volts is like how much pressure that water is at, waiting for you to open the water valve.
Watts is a measure of how much power is flowing. It’s a combination of the pressure and the flow. Amps x volts = watts.
Watt hours (volts x amp hours) is the best way to measure capacity or measure how much capacity was used. When you use watt hours, the capacity can be compared regardless of the voltage of the battery. When you use amp hours, you have to also state the voltage.
C rate is a rating of how many amps a battery can discharge without damaging itself. A 10 amp hour battery discharged at 1 c is discharging at 10 amps. At 2c 20 amps. At 3c 30 amps. A 20 amp hour battery at 1c is discharging at 20 amps. At 2c 40 amps. And so on. Generally the higher the c rate the battery is, the higher the quality of the battery.
Many types of batteries exist, and all have different advantages such as low cost, low weight, long lifepans, or high discharge rates. The first thing to consider is simply how much size do you need to get there, or get there and back. You need to allow some extra capacity for the windy day, the cold day, or just the day you didn’t get fully recharged.
I found that two rules of thumb work ok for a rough estimate of how much battery you need to go one mile at 20-25 mph.
When using 36v batteries, 1 amp hour of battery size per mile.
When using 48v batteries, .75 amp hour per mile.
So if your commute is 10 miles one way, you need a 36v 20 amp hour battery to go there and back. Or, a 48v 15 amp hour. But if you ride slow enough, you could do it on half as much.
In addition to the distance, you must choose a battery that can discharge itself at the rate the motor will be drawing it. A battery has a rating for continuous discharge. If your motor uses a 20 amp controller, you should be choosing a battery that can provide at least 30 amps continuous. Think of the ratings like you think of the red line on a car tachometer. If you want the car engine to last, you certainly don’t drive around at the red line revs all day.
For a typical e-bike motor kit, it’s pretty easy to choose a battery size. The small gear motors tend to use a 15 amp controller. A typical 10 amp hour e-bike battery with a discharge rate of 2c can easily put out 20 amps. So for the 15 amp controller nearly any 10 amp hour e-bike battery will work.
The same 2C rated battery would need to be at least 15 amp hours in size for a 20 amp controller that is common in a direct drive motor kit. So once you have a 20 amp controller, 15 amp hours is the minimum recommended size for a lower cost 2C battery. Even if the ride is pretty short, you need the 30 amp discharge rate.
48v 15 amp hours and 36v 20 amp hours are very popular sizes because they can be carried on the bike easily. 48v 20 amp hours or larger gets too big and heavy to carry easily. Most lithium batteries designed for electric bike use include a battery management system. This will help the charger correctly charge your battery, and will prevent overdischarge. Be aware that if a battery is being sold on ebay for an unbelievable low price, it’s not because it comes with great customer service if there is a problem with it.
At the higher end, batteries may have much higher C rates. 10C is common for better quality lifepo4 cells. In RC lipo batteries, 20C is considered the cheap stuff, and 90C cells are on the market. For most commuter use, there is no particular need for a C rate higher than 20C. Most commuters don’t really need a 50 amp controller, but since it’s fun, they may choose one anyway. Just remember, it’s not legaly a bike anymore in most US states with a 50 amp controller. Even with the higher c rated batteries, it’s advisable to discharge them at half the rated discharge rate. This will help improve both performance and lifespan.
Sealed lead acid batteries remain popular for their low cost. But they have very low performance compared to modern lithium. If your commute is in the easy class, lead acid can be an economical way to go. Unfortunately the weight will be very heavy. Broken carrying racks are very common with lead acid batteries. You can ruin lead acid batteries very quickly. I ruined a set in less than 30 days by discharging them too deep.
Another issue is battery monitoring. Some motor kits have a few colored lights on the throttle. They work ok for lead acid batteries. They are very crude voltmeters. They work poorly with lithium batteries because lithium batteries don’t discharge the same way lead does. The gold standard for battery monitors is the Cycle analyst. A very handy tool with many functions, but the crucial function is a wattmeter. Other less expensive wattmeters can be used. Only by measuring the watts actually used and comparing that number with the number of watts the battery is known to have provided in the past can you really have a fuel guage.
At the very minimum, a voltmeter will at least give you a more accurate measurement of battery voltage. For example, your 36volt battery should be at around 43 volts when fully charged. If you just charged it, and you only see 38volts you can be sure you didn’t get fully charged. You may want to ride very slow home tonight, since at about 34 volts, your 36v battery is completely discharged. Even though a battery monitoring system should prevent you from overdischarging your lithium battery, you will still ride with more peace of mind if you have some way to be sure the bms has not failed to stop your discharge before it gets too low. Overdischarging lithium batteries will permanently damage them.
Other problems may need solving to bring your commute to perfection. The weather is one big one. You may need to deal with keeping your battery warm enough to discharge its full capacity. Or you may have to ventilate the battery box to keep the bms from melting in 110F temperatures.
Rain is a problem, a big problem if you run slick tires. The motor will generally be ok in damp weather, but the battery, controller, and wiring plugs will need some protection. Fenders are a good start of course. Wind can slow you down a lot if your bike is low powered.
The right clothing is a must for bad weather riding. It must fit so you can pedal comfortably. For really long rides you may want to wear lycra riding shorts as underwear. The type of helmet you wear may depend on the season. In my hot climate I like a regular bike helmet in summer. I found a snowboarding helmet a good choice for mild winter riding. Full face helmets with windshields might be a better choice if you live where real winter happens. Some argue about helmets. I just say I can still type this story because I was wearing one in several crashes over the years. End of arguments for me.
Speaking of protection, gloves are nice, and eye protection is advised. I’ve had many a pebble thrown by a car tire bounce off my eyewear. Full leathers or other armor is a personal choice, but not generally considered mandatory for travel at legal 20 mph speeds. But if you plan on higher speeds, I will say for sure that crashing in full armor is much nicer than crashing in shorts and a t shirt. If you say it won’t happen to you, you are just in denial. Another type of protection is visibility clothing. I have a whole wardrobe of yellow long and short sleeve t-shirts, and a yellow windbreaker that is always the last coat on top. It helps with cars if they see you. If they aren’t looking at their smart phone that is.
The route you choose can make or break your commute. One big advantage of an e-bike is that you can take the longer but safer route easily. Use back streets, alleys, and especially bike paths if you can, rather than play dodge car on the crowded main streets. Don’t be tempted to ride on the wrong side of the street, or run stop signs. You can’t expect road respect if people see you breaking the rules of the road every day.
Costs for e-bike commuting and the savings vary. It depends on how much you have spent on the bike, vs how much your car is costing you. You see people say their e-bike commute costs 5 cents a day or whatever. That’s the cost of the electricity only, and it is very cheap compared to one gallon of gas. People who only count the cost of gas for their car are equally delusional. The real total cost is a lot more for both. For my 15 mile one way commute, I calculated the costs of my car, a Subaru Forester, at about 50 cents a mile, and the cost of my e-bike at about 15 cents a mile. I figure that every day I rode the bike put 12 bucks in my pocket. The commute takes about an hour longer than driving, so for that extra hour, I get paid 12 bucks an hour. Since I enjoy riding a bike so much, it’s all good. Only riding the bus was cheaper, but that took an hour longer than the e-bike. I was able to delay replacing my car for three extra years. Putting off the day I have a car payment again by three years was priceless. Car mileage went from 15,000 per year to less than 6000 miles. Suddenly I wasn’t spending every weekend fixing the car anymore. The cost of a typical commuters e-bike capable of 20-30 mile range is between $1000 and $1500 depending on how much is spent on the bike. Ever tried to keep a $1000 car running for long?
The health benefits of riding a bike are well known. Lots of my friends didn’t understand that I still pedal briskly on the e-bike commute, and get as much or little exercise as I want. They think with a motor, you get no exercise. Not true. Even faux pedaling, where you merely spin the pedals is great for the heart and lungs. After 6 months of regular e-bike commuting my heart and lung health improved a lot. This improved everything in my life. At middle age, keeping in shape is very hard to do compared to when you were young. A few hours spinning the pedals on the e-bike several days a week keeps me in great shape for other fun activities.
How much or little you actually use your commuter bike depends on lots of things. A warm climate helps a lot to extend the riding season, and a short commute can be tolerated in worse weather than a very long one. But one thing is certain, the e-bike is just about the least expensive and most carbon neutral transportation known to man. Commuting by e-bike is a great way to shave your transportation costs while saving the planet at the same time.