If you are fairly new to the idea of an E-bike, and you think you might want one, this article hopes to give you some info to help you get some kind of an idea about what type of kit will fit your needs.
Factory E-bikes are very expensive compared to the kits that you can get and install on your own bike, but…some people don’t mind paying more to get good customer service from a local dealer, and getting a turn-key factory E-bike that they can begin riding immediately.
But…if you are mechanically handy, and can install a basic E-bike kit yourself…the kit ideas below may save you some money. Using a kit will also allow you to use a bicycle frame that you chose yourself…to allow you to save even more money, and to also get a bike frame that is the best possible fit for you.
Before we get started, forget about the wattage ratings of the advertisements for these kits. One horsepower is 746-Watts, and the method of rating a kit is to multiply the voltage times the amps. So, a 36-Volt kit that has a controller that can use a max power of 20-Amps would be 36V X 20A = 720W.
The power that you need (or want) is further complicated because the true limit of the power you can put through a motor is how much heat it can survive. If you take a given motor and begin raising the volts, you will get some extra power, and also the motor will spin faster than it did at a lower voltage. If you begin raising the max amps, the acceleration will get faster, but…adding more amps will cause most of the heat that will kill a motor (and sometimes the controller).
Factory power ratings are rarely accurate. Legitimate sellers under-rate their kits, because so many buyers will overheat their E-bike and want to have the motor and controller replaced due to heat damage. Then, there are the other retailers…the ones that don’t answer their customer service lines…they claim their kit will put out thousands of watts and will climb anything!…and then when you melt something, they refuse to help you.
Here’s a tip about raising the power that you can use on all these kits. If you are running on fairly flat land, you can run much higher amps for some very impressive acceleration. You will draw the max amps setting for only a few seconds while the bike is speeding up, and once your top-speed stabilizes…the amps draw slides back down to a low setting that only needs to maintain your speed, and that gives the motor and controller a chance to cool down before the next acceleration.
But here’s the worst-case-scenario…you loan your E-bike to a friend who doesn’t understand this and then they ride it up a very long and steep uphill at full-throttle. With no cooling-off phase, the motor and controller overheat, and your friend has to do the “walk of shame” back to your place. This is where you should have limited the max amps the kit can provide (a Cycle Analyst E-bike computer is an easy way to adjust the amps the controller can draw).
The popular MAC is generally regarded as capable of performing very well when using 25A, but…if you live in a very flat region you could actually use more. One of the reasons the MAC has grown in popularity is because it’s one of the few kits where you can order it with a temp sensor installed inside the motor from the factory (ebikes.ca is the other seller with temp sensors). If you have a Cycle Analyst (the best E-bike computer on the market), you can easily adjust how many amps the controller can use, so you can adjust it to get the max power possible…without melting anything.
Now that all that has been said…lets get on to these system recommendations!
36V X 10A
Small front geared hub-motor…Tongxin (edit: in 2015, the Cute Q100H has proven to be popular)
The Tongxin is so tiny, most people won’t realize you have an electric motor. There are several other 250W-rated motors of similar size, but I am recommending the Tongxin because of its one quirk…even though it is considered a geared hubmotor (the motor spins faster than the wheel to aid its torque and efficiency), it uses smooth rollers instead of toothed gears.
This is both it’s greatest benefit…and greatest weakness. The big deal about the steel rollers is that…because they are smooth, this motor runs almost silently. This ultra-quiet operation can further be emphasized by using a sine-wave controller, but…even with a common square-wave controller, the small-diameter sideplates are not very resonant. Another benefit is that the drive-roller can be very small, so these have a 12:1 reduction, instead of the common 5:1 when using toothed gears.
The reason the smooth rollers are also a weakness is because almost everyone who begins using an electric motor typically wants “just a little” more power. These roller will begin to slip a bit if you try it at higher power levels, but I’m not exactly sure where the limit is…because I’ve never been very interested in these extra-small motors (which are typically rated as 250W to appeal to countries with power limits). I suppose you could use these at 24V and higher amps, but…geared motors of all sizes shed heat poorly, so I recommend 36V and then use lower amps for a long life. About 10A is reported to be just right.
I’m recommending a front wheel motor, because at 36V X 10A = 360W, the extra hassle of mounting a rear motor isn’t needed, and just about any steel forks can easily handle 360W with a single torque-arm (yes, use a torque arm, even at only 360W). The Tongxin motors have also been re-branded as ethinkar / Nuergy / Tarn.
If you want to read about others brands of the small 250W-rated geared hub motors, check these out.
36V X 15A
Front or Rear small geared hub-motor…Bafang SWXH
Our friend Kepler had decided at one point to put together a very stealthy carbon-fiber road bike, that he could ride on the bike paths near his home. In order to blend in with the pedal-only traffic, the motor would have to be small and quiet. After some research, he settled on a Bafang SWXH geared hub, mounted in the rear wheel.
This motor has teeth on its internal planet gears, and it also has more copper mass than the Tongxin, so it can take more power. These have been regularly used with 15A, so that’s a pretty safe heat level to run it at. I wouldn’t use it at less than 36V (36V X 15A = 540W), but be aware that several builders have used these at higher voltages (48V-72V) without a significant increase in the heat.
These run fairly quietly, but there is a slight buzz from the gears during acceleration. If you use a sine-wave controller, the power control will be slightly quieter. However…with motors that have internal gears, you will always have some mechanical noise.
Its possible to use a Bafang SWXH on the front wheel, but it is just about large enough to occasionally draw attention (if you are trying to fly under the radar as a stealthy electric bike). Use a torque-arm, and if it is a high-quality torque arm, just one should be enough at 540W.
The Bafang SWXH is one proven option, but at this power level, there are dozens of 250W-rated hubs that will work well.
36V X 20A
Front Geared Hubmotor…Bafang-BPM
The Bafang BPM is one of the most prolific electric bike geared hub-motors on the planet. It is pretty much the default 500W-rated motor used by every generic E-bike manufacturer in China. This motor has a large enough diameter that you can’t really hide it. If you use a front motor while conveniently mounting the weight of the battery pack on a rear cargo rack, the balance of the bike will be fairly neutral.
By using it on the front wheel, the installation is very easy. Also, by adding some pedaling, you can have 2WD. The rear wheel can have any stock gearing system that appeals to you, with as many speeds as you like. Enthusiasts of this configuration have reported that a front motor is more stable in slippery conditions, but…it also slips more on a wet uphill compared to a rear motor. Of course, there is a rear BPM available, and also a cassette-geared version (as opposed to the common 7-speed freewheel).
You can use more volts (up to 72V has worked well because of the BPM’s low pole-count), but a 36V system uses an affordable battery to go with this affordable mid-sized motor. 20A controllers are common and cheap, and if you experiment with too many amps and fry the motor or controller…they are both cheap to replace.
I don’t recommend direct-drive hubs (or high-powered hubs of any type) on the front wheel. At high power they can damage the drop-outs and lead to a crash, and at low power the geared hubs are good enough because they are lighter and they freewheel easily without a DD hubs cogging. Performance-wise, a high powered front hub (whether DD or geared) can spin out easily…instead of accelerating.
Whether you use a DD hub or a geared hub on the front forks, use two torque-arms at this power level. Kits at this level of power work very well for the US federal speed limit of 20-MPH. Also, since this power level still allows you to safely use the hub-motor on the front…you can still use an Internally-Geared-Hub (IGH, like a Nexus-7) or the standard derailleur 21-speed external sprockets.
48V X 20A
Rear Geared hub-motor…Bafang-BPM
This is a very popular combination. Geared hub-motors freewheel easily when only pedaling because they have an internal freewheel. If you limit the amps to 20A, the BPM should last a long time, and…at 48V it will have about 30% more power than when it is driven with 36V. Of course a 48V battery will be more expensive, but if you have mild hills…a rear BPM at 48V will work better than a front BPM at 36V.
A hub-motor with a Kv (turn-count) that provides 20-MPH at 36V…will likely provide about 26-MPH at 48V.
48V X 25A
Large diameter rear Direct-Drive hub…9-Continents (9C)/ebay:Yescomusa/Magic Pie/MXUS
These next two recommendations are the most popular, a large geared hub or a large direct drive (DD) hub at 1,200W. As long as you’re riding safely, kits with this power level will visually pass for the legal 750W in the USA, and 500W in Canada. A DD hub will probably remain the cheapest option at this power level because of their simple construction, but be aware the large diameter (which helps the leverage of the magnets to produce more torque-per-watt)…is also what means that these kits will never be stealthy, and people everywhere will stop you to ask what it is.
The big benefit of a DD hub is the low purchase price and quiet operation (which can be even quieter with a sine-wave controller upgrade). These often come with a 20A max controller, but there is a significant increase in acceleration when going to 25A, and also at 30A. Somewhere between 30A and 40A, they will be in danger of overheating, depending on how much time they spend at the max amps. DD hubs also have a small amount of magnetic drag when just pedaling without power (called “cogging”), so be aware the MAC geared hub listed below is lighter and freewheels easily when just pedaling. 25A is the most common max setting…high enough to have a lot of fun, low enough that it almost never overheats.
As to copper mass, these typically have a 28mm wide stator. If you live on flat land with few stops, you can use 40A every day for wicked acceleration (as long as your battery can survive that). But…if you ride up a hill that is long enough and steep enough…even just 30A will fry it…However, these are the cheap hub-motors that have been used at every voltage from 36V to 111V, so if you damage just the motor they are cheap to replace.
Any amperage above it’s saturation point will make a lot of waste heat, which is inefficient, but…drill some air-venting holes in the side-plates to let the heat out, and these motors can be abused until they scream.
48V X 25A
Rear geared Hubmotor…10T MAC
Here is an example of the MAC geared hub motor. The MACs stator is 25% wider than the BPMs, so the extra magnet width provides about 25% more power per watt that’s applied. The extra 25% of copper mass also allows more amps to be used, so I am recommending a 25A limit when you only have mild hills (for flat land, you can increase the max amps because there is plenty of cooling off time when you’re just cruising along). But…for a long steep uphill, you really have to watch the motor heat.
Once you move the battery weight to the center of the frame, the bike will have a much better balance and feel when riding. A 10T MAC using 48V will provide about a 28-MPH top speed on flat land (45-kph) when using 26-inch wheels, and it climbs mild hills very well. This is the most popular recommendation at the forum endless-sphere.com for most new users, and it has many happy customers.
Like the DD hub listed above, you can get snappier acceleration when upgrading from 25A to 30A, but you have to watch the heat! Geared hubs have a poor heat-shedding path, so if you think you may want to hot rod the motor later with 40A or 72V…get the DD hub. If you are certain you can be happy with 1,200W, then…this is the most popular combination.
48V X 25A
Small mid drive…Bafang BBS02
This kit has created a lot of buzz recently, and here is our article on it to get more details. Bear in mind the MAC kit listed above (providing the same 1,200W) will cost less, but the place where the BBS02 really shines in on steep uphills. The BBS02 uses the bikes gears (usually 7 sprockets at the rear wheel), so that it can have high top-speed on flat land, and…then you can downshift to provide awesome hill-climbing…so the motor stays up in it’s best RPM range to keep it from getting too hot.
Plus the weight of the BBS02 motor is moved to the center of the frame, to make the bikes balance as good as it can possibly be. Another benefit of mid-drives is that the tires are easier to fix when they get flat, and they seem to get flat less when there isn’t as much weight on the tire (pushing the tire down onto sharp debris).
There are a couple of user profiles where this kit truly satisfies, and is worth the extra cost. If you live where there is a power limit (like 250W in Europe/Australia, or 500W in Canada/Switzerland), this small motor will usually pass for a low-watt system. The other place where this is really worth the extra money is if you have steep uphills. You can downshift the bike so the motor remains at the higher RPMs, unlike a one-speed hub motor.
Downshifting a mid-drive on an uphill is not only more efficient, it prevents the motor from overheating when compared to a different one-speed hub-motor system that might bog down. It is reported to have an internal over-heat protection circuit for those times when you accidentally try to climb a steep hill in too high of a gear.
Mid-sized Off-Road Mid drive…LightningRods kit
About a year and a half ago, we wrote about a new kit from GNG, found here. The configuration was well laid out, and this motor is fantastic in this application, but the rest of the kit had many weaknesses, especially the 12T freewheel and the BB-cartridge. Endless-sphere member “LightningRods” began designing and making replacement upgrades for the kit until eventually, he was remaking the entire kit…except for the excellent motor.
It’s possible to use this kit on a hardtail street commuter, but where it really stands out is when it’s used on a full-suspension off-road frame. This motor has performed well at 30A, and it sheds heat well, since it is an inrunner. At 48V X 30A = 1,440W, it’s performance is outstanding! But...it gets better than that. The low pole-count means this motor can be run at very high RPMs without excessive waste-heat produced from eddy-current losses. This means that it was tried and successfully verified to run well at 72V (and also 100V!). 72V X 40A is an awesome 2,800w!
Of course, if you are running at 100V (and 100V X 30A = 3,000W), the motor is spinning fast enough that you will not be able to pedal along with the bike to help. But…at 100V, I would recommend keeping your eyes on the trail instead of pedaling! If you add a temp sensor, you can use even more amps than 30A, up to 40A. Being a mid-drive, this kit puts the motors (fairly light) weight in the center of the frame. This makes the bike more nimble compared to using a heavy rear hub.
These kits can be ordered now, but since they are unusually popular and in limited supply (while this business ramps up production to keep up with demand), it will be a lucky few that can get their hands on this kit. There may be a waiting list, but it is well worth the wait if you want a powerful and light off-roader that is robust, reliable, and will last.
If you want to run more than 3,000W, you will have to sacrifice letting the motor use the bikes gears, which is the biggest benefit of a mid-drive. 4,000W will break bicycle chains and sprockets (or at the very least, wear them out unusually fast).
48V X 20A…(times TWO for 2WD)
There have been several 2WD E-bikes featured recently. The Mental Manno from Croatia, Teklektiks Mundo commuter in the US, and Bens AWD “Duty Cycle” in Taiwan. If you scan this build index from a Russian E-bike forum, you will find a dozen 2WD E-bikes (because of the snow in Russia over half the year).
They all use one throttle and one battery, but…they also used two controllers, and two identical geared hub motors (which freewheel). So…why would someone want two smaller motors, when you could just use one very large motor (like the systems listed below this)?
There are several reasons. First of all…in slippery or extra steep conditions, 2WD will have better traction. There are some conditions where no matter how much power you have, a single motor would just spin out, instead of accelerate. Secondly, all of these builders mentioned they liked the redundancy. If you live where it is extra steep, being far from home when a motor or controller has an issue can be a nightmare. With 2WD, the second motor and controller allows you to have a “limp home” mode.
The 1,900W number above is from using Bafang-BPMs at 48V X 20A = 960W (times two motors for 1,900W), but Bens Duty Cycle uses a pair of the larger MACs, and he is running 57V X 53A = 3,000W (times two motors) for 6,000W of 2WD traction. And yes, he does have temp sensors on both motors to make sure he doesn’t fry anything. He uses a handy 3-way power switch from to limit amps when climbing, and to use max amps on flat land to embarrass drivers who think their cars are fast…
72V X 35A
Rear Direct-Drive hub…Crystalyte H35XX (available as an H3525 or H3540)
If you have sampled 35A in a rear hub…and you like it…you really need more copper mass than the common 28mm wide stators in the 9C sized DD hubs. The Crystalyte H35-series has a 35mm wide stator (25% more copper), and it still allows the use of a common 7-speed freewheel while also fitting in the common 135mm wide drop-outs of all the widely available bicycle frames.
We have featured two E-bikes so far with this well-regarded hub and all three builds have some similarities. They are Rodgah’s Big Hit FSR, and the Electra Townie by Nick. You could get more power from an even larger hub than the H35-series, but…even though these builders like the near silence of a DD hub, they didn’t want any more weight out at the rear wheel than necessary, so…they used higher volts in the smallest hub that would satisfy their needs.
After you have had a hub-motor for a while, and you decide you want a little more speed and acceleration, everyone tells you to up the volts to the most you can afford (and can fit into the frame), then…you raise the amps to the max possible while still keeping the motor under 93C/200F. For the performance of 72V and 35A minimum, the Crystalyte H35 is the most affordable and lightest hub that can reliably provide that.
But…if you read the build-logs listed above, some of these builders used 100V, along with temporary peaks of 50A (with air-venting holes in the sideplates and temp sensors), for a whopping 100V X 50A = 5,000W. If you want to spend a lot of time riding faster than 30-MPH, I recommend a DD hub instead of a geared hub. Even 2WD MACs work best when limited to 30-MPH, plus…at those speeds you really need a good front suspension, which doesn’t go well with a large and powerful hub in the front.
72V X 40A, Crystalyte H40XX (available as an H4040, H4065, H4080)
This motor has an almost identical construction as the HT35XX listed above, but it has a wider 40mm stator, and the extra copper mass will let it use more amps than the HT35XX (under the same conditions), or…it will run cooler at the same amps.
The 4080 will fit into common 135mm wide bicycle frame drop-outs, but it’s extra width means it will easily fit only a 5-speed freewheel. The core of this motor is a common stamped steel plate, so it cannot absorb as much of a temporary heat spike as the Crown motor listed below (with the Crowns’ heavy aluminum core).
72V X 50A
Rear Direct-Drive hub…The Crown
In this power category, you could use “The Crown” motor, also from Crystalyte. It uses a 40mm wide stator, which is bigger than the H35 listed above, and less than the 50mm stator on the Cromotor listed below.
The Crystalyte 4080 also uses a 40mm wide stator, but there are differences between these two motors though…the 4080 has a less expensive steel stamped core, and it also is narrow enough to allow you to squeeze in a 5-speed freewheel (not that you’ll be pedaling much with 2880W), and it uses common spokes.
The Crown is more expensive than the 4080. It uses a thick-spoked aluminum core that helps absorb temporary heat spikes, so the 4080 would be acceptable on a flatter commute, and the Crown would be preferable for frequent stops and some hills (which require more high-amp peaks). The Crown also has deeper stator slots, so it can hold more copper mass in the windings.
One limit on the Crown is that it will only fit a single-speed freewheel when using common frames, but both of these motors should still fit into any common steel-framed bicycle. If you want to use this on an aluminum frame, you will need custom steel clamping drop-outs, since this power level will likely break common torque-arms (even when using two of them).
Be aware the initial 2014 version of the Crown series used a custom spoke arrangement so that it has better spoke angles when it is mounted on a smaller wheel (the newer versions use common-style spokes). If you add a temperature sensor, and keep an eye on it, this motor should be able to use 72V X 65A for an impressive 4680W.
The Crown has four Kv’s available (ebikes.ca only retails two, the TC80, and the TC100). This may be a consideration, because the Cromotor below is only supplied with one Kv selection.
72V X 60A–100V X 80A
Rear Direct-Drive hub…Cromotor
I can’t imagine going to the trouble of buying an expensive and heavy hub motor, and running it on only 48V and lower amps, so…these recommendations will require a lot of Watt-Hours (WH) of battery volume. This is going to be the single biggest issue in this category…fitting enough battery mass on a bike frame to supply 72V-100V and also 60A-80A.
The popular choice by a longshot is the monster Cromotor, with its 50mm wide stator. The most popular frames for it are frame kits from Phasor, the Greyborg Warp, and also Qulbix Raptor. Our friend Martin built a street commuter using a robust downhill (DH) bicycle frame, but he had to order some custom rear drop-outs to accept the Cromotors 145/155mm wide axle shoulder. He also used an unconventional twin suitcase saddle arrangement to house the high-WH battery that is needed to feed this hungry beast because there was no room in the frame.
The three frame kits listed above have each chosen to house their large battery packs inside a hollow boxed frame. Any of these full-suspension frames can be run on the street…or off-road. Most of the Greyborg builders seem to be running on the street, where the muscular mass of the Cromotor is not an issue.
However, the Phasor and Raptor builders are more likely to build an off-road E-bike, as a sort-of lightweight dirt motorcycle, that can still be pedaled home on the streets due to the quiet motor (instead of a dirt-bike gasser engine). This is likely because the Phasor and Raptor frames allow a much longer rear shock than the Greyborg.
The Phasor has the slimmest frame at 100mm wide (for easier pedaling) but…if you want the absolute highest battery volume, the 160mm wide Raptor is the one. The Greyborgs 110mm wide frame is in the middle…slim enough for easy pedaling, but more battery volume for higher volts and amps.
72V X 60A is 4300W, which is the minimum watts that make the cost of a Cromotor system worthwhile, but…all of these frames have also been successfully run with a Cromotor at up to 100V X 80A for a brutal 8,000W. On frames this light, you would be shocked at how easily it can out-accelerate some VERY expensive and exotic sports cars at that power level.
Written by Ron/Spinningmagnets, March 2014