hub motor

How To Install Hub Motor Washers

Hub motors often come with a pile of odd looking washers. It can be confusing to determine exactly what each is for and how to install them.

However, installing these washers properly is crucial, because failure to do so can easily lead to damaging the bicycle or the motor. If the motor were to work its way out while riding due to improper installation, you could find yourself in a very dangerous situation. But don’t worry, this can all be avoided with a little education on hub motor hardware.

Hub motor hardware

Let’s start by taking a look at the diagram above with the different types of hardware that might come with your hub motor. Every hub motor should come with a minimum of axle washers, torque washers and axle nuts. Many come with spacer washers as well.

Axle washers are simply flat washers with a hole either 12 or 14 mm in diameter allowing them to slip over the axle of the hub motor. These can be placed anywhere on the axle, but generally go inside of the dropout and are the first type of washer placed on the axle.

Spacer washers are thicker than standard flat axle washers, usually 2-5mm thick. They also generally have a non-uniformly circular hole, as seen in the diagram above. These can go anywhere on the hub motor axle and are used when extra space needs to be filled. The most common uses are when the dropouts are too wide and thus the spacer washer goes inside of the dropouts, or when a torque arm needs to sit further away from the dropout, and thus the spacer washer sits outside of the dropouts.

Torque washers are used either in addition to, or in place of torque arms. They have a tooth that sits down in the dropout and helps apply the torque of the motor further from the center of the axle. The further away the force from the torque is applied, the smaller the magnitude of the force. For small geared motors of 500 watts or less, torque washers are usually sufficient. For direct drive motors of 750 watts or greater, torque arms may be required depending on the bicycle’s dropout material and design.

Axle nuts go on the outside of the dropouts and are the last thing to be placed on the axle. They secure the axle in the dropouts by keeping a constant force against the bicycle. Most axle nuts should be torqued to at least 25 newton meters. If you don’t have a torque wrench, a good strong turn on a 6 inch wrench is plenty. Some hub motors can have their axle threads strip when the axle nuts are torqued over 50 newton meters. This often occurs when someone uses a long wrench and really tries to tighten down hard. The nuts should be closed tightly, but you don’t need to overly exert yourself.

Installation of hub motor washers

When you install your hub motor, start with an axle washer up against the shoulder of the hub motor’s axle. This washer will go inside the dropouts and give a larger surface than the axle’s shoulder to clamp against the inside of the dropouts. There should be an axle washer on both sides of the hub motor axle, inside the dropouts.

Next, if the hubmotor slips into the dropouts easily and there remains extra room for the axle washers to move up and down the length of the axle, you may need to install a spacer. One or two millimeters of wiggle room is generally ok and can be removed when you tighten the axle nuts, but any more than two millimeters can cause chain or disc brake clearance problems and overly stress aluminum frames.

If you have extra room on your axle due to extra dropout width, either use a spacer washer or a torque washer on the inside of the dropout. This should take up the extra space on the axle and may even require you to spread the dropouts slightly to slide the motor axle down into the dropouts.

If you don’t have extra room on the axle, your torque washer can go on the outside of the dropouts. The important thing to note with a torque washer is that the tooth must be down in the dropout for it to work effectively. This is rarely an issue with 12 mm torque washers, but sometimes the tooth on 14 mm torque washers sits up too high. If this is the case in your setup, just take a hammer and lightly tap the tooth back down. Sometimes it helps to use the blade of a cold chisel or an old flat head screwdriver (that beat up flat head screw driver you keep around for prying things would be perfect) to transfer the force of the hammer directly to the tooth of the torque washer.

Lastly, add your axle nuts on the outside of the dropouts as the last piece of hardware on the axle. Tighten them down securely but don’t over torque them. As mentioned above, a good strong turn on a 6 inch wrench is plenty for most hub motors.

Keep in mind that this isn’t the only correct way to order your hardware. The important points here are that there is a washer up against the hub motor axle’s shoulder inside the dropouts, that the torque washer’s tooth is in the dropout gap, and that the axle nut is closed from the outside. This could also be accomplished by placing the torque washer on the axle first with the tooth facing out, then the axle nut on the outside of the dropout. This way the torque washer acts like the first axle washer in the images above by distributing the force of the hub motor axle’s shoulder against the inside of the dropout while simultaneously working like a normal torque washer by applying the torque load further from the center of the axle. In this scenario, there would only be two pieces of hardware used: the torque washer inside the dropouts and the axle nut outside the dropouts.

Torque arms

Torque arms protect your motor and frame similar to the way torque washers do, by resisting the rotational moment about the axle. However, torque arms are much stronger than torque washers. I wrote a whole article about torque arms, so I suggest starting with that as a primer if you don’t know if you need a torque arm or not. To summarize, if your hub motor is going in an aluminum fork, aluminum dropouts and/or your hub motor is over 1,000 watts, you likely need a torque arm.

A torque arm is almost always installed outside of the dropouts and before the axle nut. It is usually connected to the either the dropouts with strong glue or bolts, or to the frame with hose clamps. Here you can see a torque arm being included on the same example bike.

In conclusion

As you can see, installing your hub motor washers isn’t rocket science. The important factors are:

A washer is inside the dropouts against the shoulder of the hub motor axle
A torque washer is installed with the tooth inside the dropout gap
A torque arm prevents the axle from rotating in the dropout (optional depending on system)
An axle nut secures the axle from the outside

As long as those conditions are met then you should be good to go. Just remember to reinstall the washers in the correct order if you ever remove the wheel to fix a flat tire. This is especially important if you take your ebike to a local bicycle shop for a repair because most bike shops are not familiar with ebikes and might unintentionally reinstall the motor incorrectly. Always verify that your washers are correctly ordered and aligned.

photo credit 1

What is a Torque Arm and Why Do I Need One

A torque arm is an extra piece of support metal added to a bicycle frame to more securely hold the axle of a powerful hubmotor. But let’s back up and get some more perspective on torque arms in general to learn when they are necessary and why they are so important.

Many people choose to convert a standard pedal bicycle into an electric bicycle to save money over purchasing a retail ebike. This is a great option for a number of reasons and is surprisingly easy to do. Many manufacturers have designed simple ebike conversion kits that can easily bolt onto a standard bicycle to convert it into an electric bicycle. The only problem is that the poor guy that designed your bicycle planned for it to be used with lightweight bike wheels, not giant electric hub motors. But don’t worry, that’s where torque arms come in!

Torque arms are there to help your bicycle’s dropouts (the part of the bike that holds onto the axles of the wheels) resist the torque of an electric hubmotor. You see, normal bicycle wheels don’t apply much torque to the bicycle dropouts. Front wheels actually don’t apply any torque, so the front fork of a bicycle is designed to simply hold the wheel in place, not resist its torque while it powers the bike with the force of multiple professional cyclists.

Rear wheels on standard bicycles traditionally do apply a small amount of torque on the dropouts, but not more than the standard axle bolts clamped against the dropouts can handle.

Torque arms add strength to weaker bicycle frames

drawings courtesy of Grin Technologies (ebikes.ca) and used with permission

When you swap in an electric hub motor though, that’s when torque becomes an issue. Small motors of 250 watts or less are usually fine. Even front forks can handle the low torque of these hubmotors. Once you start getting up to about 500 watts is when problems can occur, especially if we’re talking about front forks and even more so when the material is weaker, as in aluminum forks.

In this case a torque arm is required to resist the torque of the hub motor. Torque arms come in all shapes and sizes. Some are mass produced, one-size-fits-most styles that slide over the axle of the motor and then clamp or bolt into the bicycle frame, offering a firm connection to the bicycle further away than the surface of the axle.

Other torque arms are custom jobs made by guys and gals in their garages, specifically suited to their own bikes and motors. The one thing all these torque arms have in common is that they grip the flat part of the motor axle and connect to the bicycle frame in a sturdy way to help resist that torque from forcing open the dropouts.

Gasp! Do I need a torque arm?!

So when do you need a torque arm? Well, the short answer is that it’s better to be safe than sorry and that a torque arm will always help. Practically speaking though, there are a few factors that will tips the scales in favor or against the need for a torque arm.

First of all, if you are buying a retail, commercially available electric bicycle then you don’t need to worry about a torque arm. The ebike’s designers will have already included one, if necessary, or more likely will have designed the bicycle to be a purpose built ebike with strong enough dropouts to not require a torque arm.

If you are doing your own electric bicycle conversion though, you might need a torque arm depending on the type of bike and power level of the motor.

As mentioned above, front and rear mounted hubmotors have different requirements. A front fork is usually much weaker than the rear dropouts. This means that front hub motors are more likely to require a torque arm than rear motors.

Next, frame material plays a big factor. Steel is a stronger material than aluminum and resists bending easier. That means if you have steel dropouts combined with a rear hubmotor, you’re in a much better position than a front aluminum fork.

Lastly you have to consider the power of the motor. Like we discussed above, 250 watts or less should be fine in nearly any steel or aluminum dropout without torque arms. 500 watts is about the limit you’d want to put in rear aluminum dropouts without a torque arm. If you have a 500 watt motor in the front, especially if you have an aluminum fork, you’ll want to use a torque arm. 750 watts or above should almost always use a torque arm, even in the rear of the bike, even in steel. Generally speaking, 750 watts in rear steel dropouts will probably be fine, but it’s getting near the limit. That’s why we recommend 750 watts or above, using a torque arm.

Torque arm specifics

Three main factors control the effectiveness of torque arms, so you’ll want to pay close attention to these when buying or making your own torque arms. First is the material choice. Look for stainless steel torque arms if possible. These will be even stronger than the mild steel or aluminum that your bike frame is made out of.

Next, thicker is better. Always. You want as much meat gripping that axle as possible. Try to find a nice thick torque arm. I’ve seen thin torque arms simply cut a slit around the axle and still allow it to spin, damaging the bicycle and motor. A quarter inch (0.635 cm) is a good torque arm thickness to aim for. Even thicker is better, of course.

Lastly, the further away the torque arm mounts to the bike, the better. A one inch long torque arm is good, two inches is better, and three inches is better yet. The further from the axle that the torque arm mounts to the frame, the more force it can resist.

Good torque arms won’t be cheap. Don’t expect to spend less than $15-20 a piece for a decent stainless steel torque arm. The good news is that you can find them all over the internet from many reputable sellers including for between $9-$38 from ebikes.ca (one of the best electric bicycle parts vendors in North America) which are also available to order even easier from Amazon, including a front torque arm here and a rear torque arm here, or for $25 from Electric Rider for a beefy Crystalyte torque arm.

If you’re in a pinch or you really want to make your own, a 10 mm spanner wrench makes a surprisingly good torque arm. Just make sure the wrench doesn’t somehow interfere with the axle nuts closing firmly.

When in doubt, use a torque arm

Torque arms are there to save your motor and your bicycle. The cost of not using torque arms when you should have is quite high: often a destroyed motor and/or destroyed bicycle frame. You can avoid this tragic end by making sure you’ve got the right tools for your ebike build, including knowing when to use a torque arm.

photo credits 1, 2, 3

Geared Hub Motors Vs Gearless Hub Motors

A powerful direct-drive hub motor

There are two main types of hub motors currently on the market: geared and gearless hub motors (gearless hub motors are also called “direct drive” hub motors). Due to the lack of gears, direct drive hub motors are the simpler of the two, so we’ll start with those.

Gearless (direct drive) hub motors

In a direct drive hub motor, the axle that passes through the center of the motor is actually the axle of the motor itself, with the copper windings fixed to the axle. This whole axle assembly is called the “stator”. The magnets are mounted to the outer shell of the hub motor. When electricity is applied to the stator a magnetic field is induced that causes the magnets to move. This in turn makes the whole shell of the motor turn and propels the ebike forward.

Inside a gearless direct-drive hub motor

Geared hub motors

Geared hub motors, on the other hand, have their cases connected to the stator through a planetary gear reduction system. For every rotation of the case, the motor inside actually turns many times faster. This allows the motor to work at higher and more efficient speeds, while still allowing the wheel to spin at a comparatively slower driving speed.

simulation of a planetary gear reduction system

How do geared and gearless hub motors compare?

Direct drive hub motors are capable of providing large amounts of torque and power. This makes them especially well suited for higher performance ebikes. Direct drive motors are usually big and heavy which adds to overall bike weight and decreases range. On the upside, this extra mass helps the motor to keep from overheating as easily because the thermal mass of the motor functions as a heat sink.

Light duty direct drive hub motors, like many found on eBay and other auction sites, are usually rated at 500 watts but can usually be operated safely at up to 1,000 watts. Bigger direct drive motors, such as Nine Continent style hub motors, are usually rated at 1,000 watts but can handle even higher power levels.

Geared hub motors are smaller and lighter than direct drive motors, which can help with increasing range, but they are also less powerful and can wear out more quickly. Most geared hub motors are only rated up to 350 watts of power, though the larger Bafang BPM geared hub motor has a rating up to 500 watts and has been successfully used on ebikes up to 1,000 watts, though with a shorter life expectancy (of the motor that is, not the rider).

Some people have had success increasing the lifespan of the plastic gears inside geared hub motors by replacing one of the three plastic planetary gears with a metal gear. This allows the metal gear to take the brunt of the stress, saving the other two plastic gears and extending the usable life of the hub motor. This generally makes the motor a little louder – though this is rarely a deal breaker.

internal plastic gears in a geared hub motor

Three plastic gears transfer power inside a geared hub motor

Choosing between a geared or direct drive hub motor usually comes down to two considerations: your power and weight requirements. If you are envisioning your electric bicycle with a lightweight setup in mind, you are pretty much limited to a geared hub motor. If you are looking for a powerful ebike, especially an ebike over 1000 watts, your best option is the direct drive hub motor.

photo credit 1, 2,

Front Hub Motors Vs Rear Hub Motors

When it comes to installing a hub motor, you’ve only got two options: a front hub motor or a rear hub motor. (There are actually a few electric bicycles with hub motors mounted as mid-drive motors, but that’s outside the scope of this article.) If you search around, you’ll probably find that the same hub motors are offered in both front and rear hub motor kits, begging the question “what’s the difference?”

Hub motors: weight matters

There are few issues to consider when deciding between a front or rear hub motor. Let’s start with weight.

Generally speaking, you want to try to spread the weight of your electric bicycle out as much as possible, front to back. You don’t want to have all the weight located in one area. Most batteries are mounted in the middle or rear of an ebike, meaning that a front hub motor helps spread the weight forward and can improve weight distribution of your electric bicycle.

Bicycles with heavy rear hub motors and batteries also mounted far to the rear, such as on a rear rack, are prone to “popping wheelies” during acceleration. This is especially true if the motor has fairly high torque and/or the wheels are smaller diameter.

oops!

While it may sound fun, this wheelie behavior can become rather annoying when it happens every time you accelerate after a red light or stop sign. It can also be dangerous if it happens when you aren’t expecting it, such as on a slight uphill. Letting someone test ride your ebike and having them flip it over on the first try isn’t good either.

Traction is affected by hub motor placement

Traction is another important consideration. While moving a hub motor forwards to the front wheel solves the problem of weight distribution, it can cause a different problem: traction control. Because there is already very little weight on the front wheel of the ebike, compared to the rear, a front hub motor has less traction.

The higher the voltage and the smaller the wheel, the more likely you are to “peel out” during acceleration with a front hub motor. 36V hub motors on a 26” can still usually get decent traction, but a 20” front hub motor wheel will almost definitely experience a spinning front tire, as will a 48V hub motor on any wheel size.

Most of your body weight is supported by the rear wheel of the bike, which is why a rear hub motor will get much more traction than a front hub motor. It would be very difficult to get a rear hub motor wheel spinning freely on a dry road with nearly any motor running at 48V or less. If you’re one of the guys pushing the limits of high voltage and high power ebikes, you can get about any wheel to spin though.

Hub motors and flat tires

Another thing to think about are flat tires. You are more likely to pick up road debris resulting in a puncture to your rear tire than your front tire.

Why? Because your front tire often kicks up objects laying on the road, such as nails, glass shards, staples, etc that were initially laying flat. They don’t cause much harm to the front tire since their flat surface isn’t sharp. Once they bounce up from the impact of your front tire though, every now and again you’ll be unlucky enough to have it land perfectly aligned to spear your rear tire as it gets passed over for the second time.

Flat tires are much more annoying to fix in a hub motor wheel than a standard wheel, so if you’ve got a rear wheel hub motor, you may find yourself with an annoying flat tire repair down the road. Regardless of whether you go with a front or rear hub motor, my article on avoiding flat tires can help you make this a non-issue.

Consider your hub motor installation

Another advantage of front hub motors is that they are easier to install than rear hub motors. You don’t have to worry about transferring over the freewheel or trying to adjust your derailleur to get rid of that funny chain noise.

With a front hub motor, you simply swap the tire on the wheel and place the motor back into the dropouts. Front hub motor installations are easier than pie, whatever that means.

Rear hub motors still have their advantages

Don’t count out rear hub motors just yet. Many people like their electric bicycle to look like a standard bicycle without any dead giveaways of their “assistance”, so to speak. Many small hub motors nearly disappear behind the gears of a rear wheel, and are often covered by the disc as well. This gives the bike an extra stealthy look and hides the dead giveaway of a naked front hub motor.

Powerful hub motors are also more appropriate for a rear installation because the higher power can be better handled by stronger dropouts in the rear of the bike.

Would you ever guess this bike has a rear hub motor?

So while front hub motors are easier to install, get fewer flat tires and help spread the weight around, but rear hub motors get better traction, provide smoother acceleration and can appear stealthier.

In practice, many small, weaker hub motors are used in the front of the bike to take advantage of the weight distribution while avoiding issues of tire spin due to the weaker motor, while larger more powerful hub motors are placed in the rear to take advantage of the gains in traction. In the end, it’s all about what works best for you.

photo credit 1, 2

Avoid Flat Tires With These Six Tips

Flat tires are one of the most frustrating things about using a bicycle for daily commuting. For ebikes, flat tires are even more annoying. Ebikes are heavier and so changing a tire can be more cumbersome. If the flat tire is on a hubmotor wheel, dealing with lifting the motor out, sometimes complicated by short hubmotor wires, really throws a kink in your plan. Changing a flat tire on an ebike can still be done, but it’s best to avoid the scenario all together, if possible. Here are 6 tips to help you avoid flat tires.

1. Avoid Flat Tires By Keeping Your Air Pressure High

Avoid flat tires by keeping your air pressure topped up!

Tires that aren’t fully inflated are a lot more likely to pick up a flat than nicely pressurized tires. Check the side of your tire to determine the proper pressure. Most standard mountain bike, cruiser and hybrid bike tires are in the 40-65 PSI range. Keep your tires in the mid to upper end of that range. As a quick gauge, try squeezing your tires between your thumb and forefingers. They should be firm, but not hard as a rock. You should feel a small amount of give.

2. Riding With Worn Down Rubber Is Asking For A Flat Tire

Don't let your tires get this bad or you'll find yourself with a flat tire in no time!

If you see the tread in your tire is worn down, or cracks appear in the rubber, change your tires. Aged, thin and rigid rubber is much easier to puncture than new, thick and pliable rubber. This is also a safety issue; you wouldn’t want to drive around with worn out, cracking tires on your car, so why would you do the same on your ebike?

3. Put Anti-Flat Tire Material In Your Inner Tubes

This stuff is great! I once had a thumbtack stuck in my rear tire for 10 months, but because the anti-flat gunk filled the hole around the thumbtack, it didn’t leak air. If you get a foreign object stuck in your tire, and it isn’t a safety issue such as a big nail that could come flying out, just leave it there. A little thorn or staple won’t cause any more damage to your tube than it already has, and the anti-flat gunk will fill the hole and basically ‘glue’ the foreign object in place, sealing your tube. Two of my favorite anti-flat tire gunks are green slime and Joe’s tire sealant.

4. Try Not To Ride On The Side Of The Road

Avoid the shoulder, take the lane! The side of the road is flat tire heaven!

The side of the road is where all the crap from the road gets kicked up and eventually deposited. It’s full of road debris like broken glass, nails, staples, thorns, etc. Even a piece of broken plastic tail light can puncture a tire if you catch it at the right angle. If possible, ride out in the lane with the cars. If you live in a city, your ebike can probably match city speeds so this shouldn’t be a problem. If you are on a road where cars travel faster than your ebike, move over to the side whenever necessary for safety’s sake, but try to return to the lane when possible. Also, avoid riding in the dead center of the lane, since most cars straddle the center with their tires, causing road debris to accumulate in the very center of the lane where tires don’t contact the road. Ride slightly off-center in the ‘track’ made by the right side tires of cars.

5. Use Tire Liners, But Only Good Ones

If you are going to use tire liners, go with a soft, pliable rubber type, and choose a high quality type like Mr Tuffy tire liners. Cheap tire liners can actually CAUSE flat tires. When I lived in Pittsburgh, after the cold winter I found my plastic tire liners had become rigid and broken into hundreds of sharp little plastic shards – not what you want dancing around with your inner tube.

6. Upgrade To Better Tires

Hookworm tires rarely experience a flat tire

If you spend a lot of time on your bike, this will be a worthy investment. Your tires are the only connection between your bike and the road (on a good day) so shouldn’t you make that connection as good as possible? You can get some great tires without breaking the bank if you know what to look for. My favorite all-around tire is the Maxxis Hookworm. It’s great for street use and can take some trails and light offroading too. The rubber is thick with incredible grip, meaning you can really lean into those turns. I’ve never had a flat with my hookworms. That doesn’t mean they are 100% puncture-proof, but having good rubber makes a big difference.

There’s no such thing as an entirely flat tire-proof inner tube system, and flat tires are something that we all have to deal with every now and again. Avoiding them by following these tips is your best bet to delay your next flat for as long as possible.

Lastly, make sure you are prepared for the inevitability of a flat tire, should it happen in the future. Always keep a few tools on your bike so that you can repair a flat in a jiffy if you need to. Check out my ebike emergency kit for all the tools I recommend keeping on your bike.

Photo credit 1, 2, 3, 4