Ebike hub motors can be installed in either the front or the rear wheel. Both motor placements have their own advantages and disadvantages. To help you decide, this guide explains the differences between front hub and rear hub motors. I’ll also outline the pros and cons of riding a front hub vs rear hub motor ebike.
In this guide, we’ll cover ride quality, traction, maintenance, weight distribution, handling, parts compatibility, and more. We’ll also talk a bit about mid-drive ebikes and different power delivery systems including pedal assist and throttles. Hopefully, this guide helps you choose the best hub motor placement, whether you’re buying a new ebike or installing a hub motor ebike conversion kit on your existing bike.
What is a Hub Motor?
Hub motor ebikes have an electric motor built into one of the hubs. The hub motor takes the place of a standard hub. The motor directly powers the wheel it’s built into. This drives the bike forward.
In most cases, the hub motor is installed in the rear wheel but it can also be installed in the front. A hub motor is completely separate from the bike’s drivetrain. It is not affected by shifting the bike’s gears.
Hub motors turn electricity into propulsion. Electricity is stored in the bike’s battery. Electric current runs from the battery to the hub. In the hub, the current runs through a series of wires that are tightly coiled. The wires are fixed in place, firmly attached to the axle. This is called the stator.
These coiled wires sit between the poles of a ring-shaped magnet. This is called the rotor. The ring-shaped magnet freely rotates around the coiled wires with the help of hub bearings. The magnet is attached to the hub shell. The spokes attach to the shell and the rim attaches to the spokes.
When an electric current is run through the coiled wires, the magnet rotates around the wires. This force propels the bike forward. For more in-depth info, check out this detailed guide about how hub motors work.
There are two types of hub motors: direct drive and geared. Direct drive hub motor ebikes have a large electric motor that is designed to spin at the ideal RPM for bicycles. The motor has no moving parts other than the hub bearings. These motors are heavy and reliable. They do produce a bit of resistance while coasting. This can reduce efficiency.
Geared hub motors use a smaller motor that runs much faster. The motor has planetary gears inside that reduce the RPM to the ideal speed for a bicycle. The gears allow a smaller and lighter motor to produce sufficient torque and speed. The smaller motor is more energy efficient. The drawback is that the gears increase complexity and reduce reliability somewhat. Geared motors produce less resistance, which increases efficiency.
Most hub motor ebikes have a pedal assist power delivery system. When you pedal, the motor engages automatically. Different sensor systems are used including cadence sensors and torque sensors. Cadence sensor based pedal assist is the most common.
Cadence sensors measure if you’re pedaling with a series of magnets that pass by a sensor. Some models measure your pedaling speed as well. When you start pedaling, the cadence sensor sends a signal to the bike’s control unit or computer. The control unit then turns the motor on and supplies power to the wheel to drive you forward. When you stop pedaling, the cadence sensor signals the motor to cut off. The ebike stops producing power.
Hub motors supply a constant level of power when you pedal. Many models allow you to adjust the level of pedal assist. There may be 3-5 settings to choose from. On the lower setting, the motor provides less assist. On the higher setting, the motor provides more assist. You change the level of assist with a handlebar-mounted display.
Some models can adjust the power automatically based on your pedaling speed or cadence. The sensor measures your pedaling speed. Once you reach a certain predefined threshold, the power reduces. Once you fall below that threshold cadence, the power increases again.
Higher-end hub drive ebikes come with torque sensors. These use a precision strain gauge to measure your pedaling power. The sensor sends this information to the control unit, which controls how much power the motor supplies. The motor’s power automatically increases or decreases depending on how much power you supply to the pedals. For more info, check out my guide to torque vs cadence sensor pedal assist.
Many hub motor ebikes also have a throttle mounted to the handlebars that you operate with your hand to control the motor speed. The throttle can be a twist grip, thumb lever, or a simple on/off button. When you use the throttle, you don’t have to pedal. The bike rides like a motorcycle or scooter. The throttle wires transmit the throttle information to the bike’s computer. For more info, check out my guide to pedal assist vs throttle controlled ebikes.
What’s the Difference Between Front and Rear Hub Motors?
This is pretty self-explanatory. An ebike with a front hub motor has the motor built into the front wheel. An ebike with a rear hub motor has the wheel built into the rear wheel.
Front and rear hub motors work the same way. They use the same technology. In some cases, they are interchangeable, as long as they are compatible with your bike’s frame.
Generally, front hub motors are physically smaller than rear hub motors. They need to be slightly smaller because front hubs have narrower dropout spacing. They also tend to be less powerful. Rear hub motors tend to be larger and more powerful.
The biggest difference between front and rear hub motors is that rear hub motors are designed to fit a cassette or freewheel. They have either threads to attach a freewheel or a freehub body. Most rear hub motors are designed to fit a standard threaded freewheel.
Front Hub Motor Pros and Cons
- Better weight distribution- The weight of the motor and battery are divided between the front and rear axles.
- Flat tires are easier to repair-Front flats are less common than rear flats.
- Lighter- Front hub motors weigh 2-5 pounds less than rear hub motors.
- More drivetrain options- You can use an internal gear hub, 1X gearing, or belt drive.
- Compatibility- If you’re converting your bike, you don’t have to worry about gearing compatibility.
- Easy installation- If you’re converting your bike, it’s easier to install a front hub motor.
- Poor traction- The front wheel can lose grip and spin out easily during acceleration.
- Harsher ride- The weight of the motor makes the front of the bike drop faster and harder when you hit a bump.
- Poor handling- The weight of the motor makes it harder to turn the handlebars quickly and precisely.
- Less durable- The motor can put additional stress on the fork arms. Over time, they can fatigue and fail.
- Fewer ebike options- Front hub drive ebikes are less common.
- Less stealthy- Front hub motors are more visible.
Rear Hub Motor Pros and Cons
- Better traction- The extra weight of the motor increases friction between the tire and the ground.
- Smoother ride- Many rear hub drive ebikes have fork suspension or full suspension to smooth out the ride.
- Better handling- Rear hub drive ebikes are easier to steer at low speeds.
- Durability- Rear dropouts are stronger. They can handle the torque of the motor without fatiguing and failing.
- More ebike options- Most ebikes have a rear hub motor.
- Looks- Rear hub motors are more stealthy. They can be hidden by the freewheel and disc brake rotor.
- Poor weight distribution- All of the weight is on the back of the bike.
- Flats are harder to repair- You need to disconnect the motor and deal with the heavy weight of the motor.
- Heavier- Rear hub motors usually weigh 7-10+ pounds.
- Fewer drivetrain options- You have to use a cassette or freewheel and chain drivetrain.
- Compatibility can be an issue- If you’re installing a hub motor, you need to make sure it’s compatible with your gearing.
Front Vs Rear Hub Motor Ebikes
There are benefits and drawbacks to having the motor in the front and in the rear. You’ll have to make some compromises. In this section, I’ll outline the main things to consider when deciding on your ebike hub motor placement.
The weight of the motor and battery affect the handling of your ebike. Ideally, you want the weight to be distributed 50/50 between the front and rear axles. You don’t want all of the weight on one end of the bike or the bike will feel unbalanced while you ride.
Front hub motors distribute weight better. This is because most of the bike’s weight naturally sits near the rear. The battery is usually mounted toward the center or rear of the bike. Most of the rider’s weight also sits on the rear.
Having the weight of the motor at the front of the bike and the battery toward the rear helps to distribute the weight more evenly. In other words, the weight of the front hub motor helps to balance the bike. The bike’s center of gravity remains near the center of the bike.
This balance makes the bike feel more natural to ride. You don’t feel the weight of the motor and battery quite as much when they’re evenly distributed. This improves ride quality and handling. The bike also feels more stable while maneuvering at low speeds.
Rear hub motor ebikes usually have the weight of the heavy motor and battery located toward the rear of the bike. Most of the rider’s weight also sits near the rear due to the placement of the seat. This makes the bike very rear-heavy.
The weight of the motor and battery feel much more noticeable when they’re both located at the back of the bike. The bike feels unbalanced. You can feel the weight of the motor more while maneuvering. Particularly while traveling at low speeds.
Another major drawback of having all of the weight at the rear of the bike is that the front wheel can come off the ground during quick acceleration and while climbing steep hills. You’ll pop wheelies if your bike has a high torque rear hub motor or small diameter wheels.
This can get annoying. You have to be careful while accelerating hard. You don’t want your front wheel to come off the ground every time you accelerate away from a stoplight or accelerate while climbing a hill. This can also be a safety issue. If you need to accelerate quickly away from a traffic situation, you want both wheels to stay on the ground. It can be dangerous if your front wheel lifts up when you’re not expecting it.
One problem with all hub motors is that they can create a gyroscopic effect while you’re riding at high speeds. When you lean the bike, the heavy spinning motor tries to right itself. This can affect the bike’s steering. This gyroscopic effect is more noticeable on front hub motor ebikes. You’ll feel it when turning the handlebars in certain situations.
Winner: Front hub motor bikes have better weight distribution.
Rear hub motor ebikes offer better traction than front hub motor ebikes. This is because more weight sits at the rear of the bike. Most of your body weight plus the weight of the motor and battery are supported by the rear axle.
The extra weight on the rear wheel increases the friction between the tire and the ground. This makes the rear tire less likely to lose traction and spin out during hard acceleration or while cornering.
You can accelerate harder when starting from a stop and while exiting a corner while riding a rear hub motor ebike. You can also lean a bit harder without your tire sliding out from under you. This allows you to maintain a higher average speed.
It’s harder to get traction when the motor is in the front hub because there is very little weight on the front wheel. Most of your body weight sits toward the rear of the bike. This means there is less friction between the front tire and the ground. During acceleration, the front tire can easily lose traction and start spinning out. You can’t accelerate quite as hard or fast with a front hub motor ebike.
The motor’s power and the bike’s wheel size also play a role in the traction. High-powered motors make it easier to spin your wheels out. Small diameter wheels spin out easier than larger diameter wheels.
For example, a 500-watt 48-volt front hub motor on an ebike with 20” tires would easily lose traction. The motor has too much power. It would be difficult to spin the wheel out on a rear hub motor ebike with the same configuration. A 250-watt 24-volt front hub motor on an ebike with 700c wheels will be much harder to spin out. With a powerful enough motor, you can spin the wheels out on any ebike.
Of course, your traction also depends on the surface of the road. When you’re riding on loose gravel or dirt, you’ll get less traction than you get on the pavement. On pavement, it’s possible to get enough traction to wheelie a powerful rear hub motor ebike.
Your tires also play a major role in your traction. Wider tires increase traction by creating a bigger contact patch with the ground. More tread touches the ground. Knobby tires can increase your grip on loose and soft surfaces by digging into the ground.
In some situations, it’s important to consider the environment while riding your ebike. An overpowered ebike that loses traction easily can cause damage to trails and nature if you ride off-road. Spinning your tires can dig ruts which can change water flow, widen trails, and damage ecosystems. If you only ride on the pavement, you don’t have to worry about this.
Winner: Rear hub motor ebikes offer better traction because more weight sits near the rear of the bike.
Flat Tires on Hub Motor Wheels
In cycling, rear tire flats are more common than front tire flats. Sharp objects, such as nails, staples, shards of glass and metal, and other debris tend to puncture the rear tire more often than the front.
This is because most sharp objects tend to lie flat on the road. When you ride over them, your front tire usually doesn’t get damaged because the flat side isn’t sharp. The impact of your front tire rolling over the sharp objects kicks them up and upends them just in time for your rear tire to hit them. Once in a while, a sharp object will land in the perfect position to puncture the rear tire.
Flat tires are harder to repair on a wheel with a hub motor than on a standard wheel. The job takes longer and you have to be more careful. It also requires a bit more effort. There are a number of reasons for this.
First, you’ll have to disconnect the motor before you can remove it from the bike. This involves unplugging a cable. When you replace the wheel, you’ll have to reconnect it again. This isn’t a difficult job but it is an extra step. While disconnecting and re-connecting the cable, you have to make sure the connection doesn’t get damaged or contaminated with moisture or debris.
The wheel with the hub motor is significantly heavier than a standard wheel. Hub motors weigh 8-10 lbs (3.6-4.5 kg). It’s harder to remove and replace a tire from a heavier wheel because the wheel is more cumbersome. You have to lift the extra weight of the motor when removing and reinstalling the tire in the bike and while removing and reinstalling the tire. It requires more effort to move the heavy wheel around.
The wheel with the hub motor is also more fragile. You have to be careful while working on it. You don’t want to drop it and damage the motor. Hub motors are pretty robust but they can get damaged if you drop them or knock them around too much. Particularly if they are geared. Geared hub motors have more moving parts.
When the motor is in the front hub, you won’t have to deal with repairing flats on the hub wheel as frequently because front flats are much less common. This saves you time and stress. Flats are much easier to repair on the wheel without the hub motor.
There are some ways to reduce the number of punctures you have to deal with. You can run tubeless tires. These have a liquid sealant inside that fills most punctures before the air leaks out and the tire goes flat. You don’t even notice punctures. Alternatively, you could run tubes with sealant inside. These do the same thing. You can also run puncture-resistant tires. These have a protective strip of hard material inside, such as Kevlar. They are also thicker. This reduces the frequency of punctures. For more info, check out this guide to avoiding punctures on ebikes.
Winner: Front hub drive ebikes because the front wheel gets fewer flats. Rear flats are harder to repair when the motor is in the rear hub.
Front Hub Vs Rear Hub Motor Weight
Front hub motors are usually lighter than rear hub motors. This is because front hub motors must be smaller to fit between the more narrow front dropouts. Standard front dropouts have a spacing of 100mm. Rear hubs have a spacing of 135mm on average. The smaller motor contains less material so it weighs less.
Most front hub motors are also usually geared. They tend to be smaller and less powerful than rear hub motors. A lightweight 250w model may weigh around 3.5 lbs.
Rear hub motors are often big and heavy. Particularly direct drive (gearless) models. Many models weigh over 10 lbs. If you’re concerned with weight, there are lighter geared options available.
The lighter weight of front hub motors makes the bike easier and more efficient to ride when you’re not using the motor. When the motor is engaged, the weight difference doesn’t really matter.
More important than the weight of the motor itself is weight distribution. You want the weight of the motor and battery to be disturbed as evenly as possible between the front and rear axles. Front hub motors do a better job of distributing weight than rear hub motors.
Winner: Front hub motors are often lighter than rear hub motors. On average, a front hub motor weighs 2-5 pounds less than a rear hub motor.
Hub Motor eBike Safety
Rear hub motors are safer than front hub motors. This is because rear dropouts are stronger. They can handle more torque without bending or breaking. They are less likely to fail and cause you to crash.
Some forks are not strong enough to handle the torque produced by a front hub motor. Over time, the force created by the motor can cause the dropouts or fork blades to fatigue. Eventually, they can fail, causing you to crash.
If your dropouts were to fail while you were riding, your wheel could come off. Your chances of getting injured are higher if your front dropouts fail. A fork failure is extremely dangerous. A crash at speed can cause severe injury or death. A rear dropout failure is also dangerous but the crash is likely to be less severe.
The frame and fork material are also important considerations. It is safest to only run a hub motor in a steel fork or frame. Steel is much more durable than either aluminum or carbon fiber. It’s less likely to fail. Having said this, many riders have installed hub motors in aluminum and carbon frames. Is generally not recommended.
Regardless of your frame material and motor location, you should regularly inspect your ebike’s frame tubes and dropouts. Ebikes in general put a lot of stress on frames. The motor creates more torque than a human can.
Look for cracks or dents in the fork arms, seat stays, and chainstays. Check all of the welds for cracks or crimping. Inspect the dropouts for cracks. If you spot any frame damage, replace the frame or take the bike to a professional for an inspection or repair.
To increase safety, it’s a good idea to install a torque arm on your hub motor ebike. A torque arm is a metal brace that prevents the axle from rotating in the dropouts. The torque arm transfers some of the force from the axle and transfers it to a stronger point further up the frame or fork.
Without a torque arm, the motor’s power can sometimes pry the dropouts open. When this happens, the axle begins spinning freely and severs the cable. The wheel can also fall out, causing you to crash. For more info on torque arms, check out this useful guide.
For more general info on safety, check out my guide: Are E-Bikes Safe?
Winner: Rear hub motors are safer than front hub motors.
Comfort and Ride Quality
Front hub motors can make the ride feel harsh. When you hit a bump or pothole, the extra weight of the motor makes the front of the bike drop harder and faster. You’ll feel more bumps in your hands and bottom. This can make for an uncomfortable ride. This rough ride can be an issue if you have back or joint problems. The extra bumps can cause pain.
It is possible to install a small front hub motor in a suspension fork. This can smooth out the ride but is not recommended for safety reasons. The pulling from the motor can damage the suspension components over time and cause the fork to fail.
Rear hub motors usually offer a more comfortable ride. You can safely use a suspension fork with a rear hub motor. Some ebikes come with full suspension. This can really make the rider smoother and more comfortable. As an added benefit, the suspension helps increase traction and handling.
On a hub drive ebike, the weight of the motor is unsprung because the weight is in one of the wheels. This means the suspension system can’t accommodate the weight of the motor. The added weight of the motor makes bumps feel harsher. If you plan to ride off-road or on rough terrain frequently, you may be better off with a mid-drive ebike.
The tires can also play a big role in ride quality. Wide, high-volume tires can help to absorb bumps and vibrations. Firm and narrow tires can create a rougher ride.
Winner: Rear hub motor ebikes are more comfortable.
Front hub motor ebikes can be harder to steer at low speeds. This is because the weight of the motor makes it harder to turn the handlebars quickly. You have to turn the heavy motor with the wheel. You might not be able to quickly move the handlebars to balance the bike or navigate tight spaces. This makes steering at low speeds a bit of a challenge. While riding at higher speeds, the weight of the motor is less noticeable. Wide flat handlebars can help make steering easier by providing more leverage.
On a rear hub drive ebike, the weight of the motor doesn’t affect low-speed steering. The handlebars remain light and nimble. This low-speed steering performance comes in handy while riding through dense cities and off-road.
A heavy hub motor can create a gyroscopic effect. When you lean the bike, the wheel tries to right itself. This can affect the steering while you’re riding at higher speeds. The bike can feel like it’s resisting your turns. It doesn’t want to lean into corners. You may not be able to corner quite as hard as you’re used to when you use a hub motor.
Winner: Rear hub motors because you don’t have to deal with the weight of the motor while turning the handlebars.
Front and Rear Hub Motors and Frames
One potential issue with front hub motors is that they may damage your bike’s fork over time. The motor causes the fork blades to flex when it engages. This flexing can cause the fork to fatigue and wear out faster than it normally would. Eventually, the fork can fail. For this reason, it’s best to limit front hub motors to 750 watts or less. More powerful motors can cause excessive fork flex and premature failure.
The constant pulling from the motor can also cause the headset to wear out a bit faster. You might need to grease or replace your headset a bit more often when you use a front hub motor.
Rear hub motors are less likely to cause frame failure. This is because the rear dropouts and rear frame triangle are more robust than the fork and front dropouts. When you use a rear hub motor, you don’t have to worry as much about putting additional wear and tear on the frame. You should still inspect the condition of the frame periodically. If you spot any cracks or crimping, repair or replace the frame.
The frame material is also an important consideration when deciding between a front and rear hub drive motor. Most ebike builders recommended against installing a hub motor in a carbon or aluminum frame. The reason is that these materials are much more brittle and susceptible to fatigue than steel. The torque forces from the motor can cause some frames to fail over time.
If you’re planning to run a front hub motor in a carbon or aluminum bike, it’s a good idea to replace your fork with a durable steel model. If you’re planning to run a rear hub motor, you should choose a low-powered model. A 250 watt motor would work well.
To increase reliability and safety, you should always install a torque arm on your hub motor ebike, regardless of the frame or fork material. A torque arm braces your dropouts and reduces the likelihood of dropout failure. Without a torque arm, the motor can sometimes pry the dropouts open, causing the wheel to fall out.
Winner: An ebike with a rear hub motor is usually more durable and long-lasting than an ebike with a front hub motor due to the strength of the frame.
Most off-the-shelf ebikes come with rear hub motors. When buying an ebike, you’ll have far more options to choose from if you choose a rear hub motor model. You can find ebikes with a range of motor sizes including 200w, 250w, 300w, 500w, 750w, 1000w, 1200w all the way up to 5000w. You can find rear hub motor ebikes with cadence sensor or torque sensor pedal assist. This allows you to choose from pretty much any style of bike including road bikes, mountain bikes, folding bikes, commuters, tandems, etc. Pretty much every configuration is available in rear hub drive.
Front hub motor ebikes are much less common. In fact, most front hub ebikes are conversions. Some folding bikes, such as the Brompton electric, use a front hub motor. You can also find front hub drive recumbent bikes. Running a front hub motor limits the motor size you can run. Front hub motors usually top out at 750w. Many front hub motor ebikes only feature a throttle. Some come with cadence sensors. A few come with torque sensors. Options are a bit more limited.
One major benefit of using a front hub motor is that you can use whatever type of drivetrain you want. For example, you could use an internal gear hub. This is nice because it allows you to shift gears while you’re stopped. You could also use a belt drive system instead of a chain. This reduces maintenance. Alternatively, you can choose from 1X, 2X, or 3X gearing. You can use modern 12 speed cassettes with electronic shifting. You can use a drivetrain from whatever brand you want.
It’s also possible to install a front hub motor on pretty much any bike. You don’t have to worry about compatibility with the drivetrain. It is important to consider whether or not your fork is strong enough to withstand the forces generated by the motor. If you want to convert your existing bike into an ebike, a front hub motor often gives you more options.
Yet another option to consider is the mid-drive motor. For more info, check out my guide to hub motor Vs mid-drive ebikes.
Winner: Rear hub motors give you more ebike motor and power delivery options. Front hub motors give you more drivetrain options.
One drawback to ebikes, in general, is that the motor puts additional stress on some of the bike’s components. When you ride an ebike, you’ll have to replace your tires more frequently because you’ll be riding at higher speeds and covering more ground than you do on a non-powered bike. Tires wear out faster. Brake pads also need to be replaced more frequently because slowing the bike down from high speeds wears the pads out faster. With a front hub motor, you may have to grease or replace your headset a bit more frequently because the pulling forces from the motor cause it to wear faster than normal.
The hub motor itself requires no maintenance. It is a sealed unit. To keep it operational, all you have to do is replace the hub bearings when they wear out. You also need to keep the hub clean and dry so it doesn’t get contaminated with debris or start to rust.
Winner: Front and rear hub motor ebikes require the same (low) maintenance.
Hub Motor Durability, Reliability, and Longevity
Front and rear hub motors are both equally durable, reliable, and long-lasting. After all, they are the same motors using the same technology.
If you want the most durable and reliable motor, choose a direct drive model. These are the most simple mechanically. They have no moving parts inside that can wear out. There are no gears. As long as you grease the bearings and keep the hub dry and free of rust, the hub should last many thousands of miles.
A direct drive hub motor can last 10,000+ miles if you take care of it. In terms of hours, a direct drive hub motor can last 250-5,000 hours. They are long-lasting.
Higher-end hub motors come with internal planetary gears that reduce the RPMs. These models are smaller, lighter, and more efficient. They are a bit less durable and reliable because there are moving parts inside that can wear out and fail over time. If an internal gear fails, you’ll have to replace the motor in most cases. Geared hub motors don’t last quite as long as direct drive hub motors, on average.
Hub motors, in general, are not very repairable. If something breaks in the motor, it’s often easier to just replace the whole unit. They’re basically disposable. It is possible to open up the motor and replace parts but finding parts for your specific motor can be a challenge. Most bike shops won’t open up an electric motor and attempt to repair it. In some cases, you may be able to ship the motor to the manufacturer for repair. They may just sell you a new motor instead.
Individual ebike components can be replaced if they wear out or break. For example, if the handlebar-mounted control breaks, you can buy a new one from the manufacturer and swap it out. If a wire gets damaged, it can be replaced.
For more info on longevity, check out my guide: How Long Do Electric Bikes Last?
Winner: Both front and rear hub motors are durable and reliable. If something breaks, it’s usually possible to repair or replace it.
Front Vs Rear Hub Motor eBike Looks
Some riders prefer the look of rear hub motor ebikes because the motor is less noticeable. A small hub motor can be hidden behind the gear cluster and disc brake rotor. The frame looks completely normal. This makes your bike appear stealthier. The average person might not even notice that you’re riding an ebike. Front hub motors are harder to hide. The large hub makes it obvious that you’re riding an ebike.
Of course, if you want to build a stealthy ebike, you’ll also have to find a way to hide the battery. Mounting the battery on a rear rack is a common option. It is also possible to mount a small battery in a piece of luggage. Some higher-end ebikes have the battery integrated into the frame.
Winner: Rear hub motors are less noticeable. This is ideal if you prefer a stealthier-looking ebike.
Hub Motor eBike Power Delivery Systems: Pedal Assist and Throttle Systems
There are two power delivery systems available for ebikes: Pedal assist and throttles. Pedal assist systems engage the motor when you pedal. This gives you a little extra boost as you ride. You have to pedal for the motor to provide power.
Throttle systems are controlled by a handlebar-mounted control. You twist the grip, press a lever, or press a button to engage the motor. You don’t have to pedal to use the electric motor. Both front and rear hub drive motor ebikes are available with both power delivery systems.
Generally, you have more power delivery system options if you go with a rear hub motor ebike. Entry-level to mid-range models often come with cadence sensor pedal assist. Higher-end models offer torque sensor pedal assist. Many models also feature a throttle, where legal. You can find pretty much any configuration you desire.
Front hub motor ebikes are a bit more limited. Most basic systems only come with a throttle control. Many models also come with a cadence sensor pedal assist system. Torque sensors are rare on front hub motor ebikes.
For more in-depth info, check out my guide to pedal assist vs throttle controlled ebikes.
Winner: Rear hub motor ebikes come with more power delivery options. Cadence sensors, torque sensors, and throttles are all available on hub motor ebikes.
Front and Rear Hub Motor Compatibility
If you’re planning on installing a hub motor conversion kit on your existing bike, there are a few things you’ll have to consider to ensure that it’s compatible. The motor must match your hub spacing, axle type, gearing system, brake type, and wheel size.
Not all hub motors can fit all bikes. Sometimes you’ll run into compatibility issues. Generally, you’ll run into fewer compatibility issues if you go with a front hub motor than a rear hub motor.
In this section, I’ll outline a few of the most important things to consider when buying a front or rear hub motor to install on your bike. For more in-depth info on ebike hub motor compatibility, check out this great guide. If you’re buying a prebuilt ebike, you don’t have to worry about any of this.
In order for the hub motor to fit your bike, it needs to match the hub spacing on your dropouts. A number of different dropout spacing sizes exist. Hub motors also come in different widths to accommodate frames with different dropout spacing.
If your bike frame has standard spacing, you won’t run into any compatibility issues. If your frame has odd-sized spacing, you’ll have fewer motor options to choose from. In some cases, you may have trouble finding a suitable motor to fit your bike.
Standard hub spacing is 100mm or 110mm for the front and 130mm,135mm, and 142mm for the rear. Most modern bike frames these hub spacing sizes. The standard width of most hub motors is 138-139mm. These can fit most bikes.
If your bike uses standard spacing, you won’t have any problem finding a suitable hub motor. You may need to bend the dropouts a couple of millimeters in one direction or the other to make the motor fit. This isn’t an issue, as long as your bike has a steel frame.
Different types of bikes come with different hub spacing. For example, many mountain bikes come with 148mm rear spacing. This is called boost spacing. Folding bikes often have 75mm front hub spacing. Fat bikes and downhill mountain bikes often have 150mm rear hub spacing. Tandems and recumbents sometimes use non-standard spacing as well.
If your bike has an odd-sized rear hub spacing, you’ll have fewer rear hub motor options to choose from. Sometimes, it can be difficult to find a hub motor that will fit. In most cases, you can find a compatible motor but you may not be able to get exactly what you want.
If you’re unable to find a compatible rear hub motor, it may be easier to fit a front hub motor because front hub spacing is more standard. Most modern bikes have 100mm or 110mm front hubs. If you’re having trouble finding a motor that will fit your bike, you can replace the fork with a wider model.
If your bike’s frame or fork is made from steel, it is possible to spread the dropouts 5-10 millimeters to make your hub motor fit. This is called cold setting the frame. You can read about this process here. Carbon fiber and aluminum frames can’t be adjusted. You may be able to get away with spreading the dropouts 1-3mm but it is somewhat risky.
Quick Release or Thru Axles
You need to choose a hub motor that matches the axle type that your frame is designed for. There are two types of axles: quick release and thru axles. The two axle types are not cross-compatible. You can’t install a standard hub motor in a bike with thru axles. You need a special thru axle compatible motor.
The vast majority of hub motors are designed to fit standard slotted dropouts, which are designed for quick release axles. The hub simply slots into the dropout and locks in place with a bolt. The slot usually measures 9.7-10mm wide. If your bike has quick release axles, you won’t have any trouble finding a compatible motor.
These days, thru axles are becoming increasingly common. In the past, they were only found on high-end mountain bikes. Now, many road bikes, commuters, touring bikes, and hybrids come with thru axles. Unfortunately, the ebike industry hasn’t really kept up. There aren’t many thru axle hub motors on the market. If your bike has thru axles, your options are limited.
One nice thing about thru axles is that there are fewer sizes. Most front thru axles measure either 12 x 100mm, 15 x 100mm, or 15 x 110mm. Rear thru axles come in 12 x 142mm and 12 x 148mm. You can find both direct drive and geared front and rear hub motors that are available or all of these thru axle sizes.
If you can’t find a hub motor that is compatible with your thru axle frame, one option is to install a new fork with quick release dropouts. This allows you to use a standard front hub motor.
One common issue with quick release frames is that the dropout slots can be a bit too narrow to fit the 10mm hub motor axle. If the slot is 9.7mm, the standard 10mm ebike axle may not fit. The solution is to use a hand file to widen the slot slightly so the axle can fit. Alternatively, you can file down the axle so it fits in the slots. This way, you’re not removing any material from the frame. Usually, you only have to remove a fraction of a millimeter of material for the axle to fit.
For more info, check out my guide to quick release vs thru axles.
Freewheel or Freehub Hub Motor
You’ll also have to choose a hub that is compatible with your bike’s gearing. Hub motors are available for both freewheel and freehub systems. The main difference between a freewheel and freehub is the placement of the mechanism that allows you to coast.
Freewheel systems have the coasting mechanism built into the gear cluster. Freehub systems have the coasting mechanism built into a separate piece called the freehub body. This part attaches directly to the hub. For more in-depth info, check out this guide.
Most hub motors use the older freewheel system. The freewheel is a single unit that usually has 5, 6, or 7 gears. It threads directly onto the hub motor’s shell. If the bike you’re converting has a freehub, you might be able to simply swap it to your new hub motor. Some kits include a new freewheel already threaded onto the hub motor.
If your bike uses a freehub system with a cassette, you might have to downgrade from a 9, 10, 11, or 12 speed cassette to 7 or 8 speed freewheel. 9 and 10 speed freewheels are available but the quality of these is often low quality. They make shifting a bit less smooth. This may require you to also swap out your derailleurs and shifters.
There are also hub motors available that are designed for the newer freehub system. These use a standard Shimano freehub body and cassette. If your bike has a 9, 10, 11, or 12 speed drivetrain, you’re better off going with one of these motors. This way, you can transfer over your existing cassette and maintain your current gearing. If you decide to use a freewheel motor, it’s best to downgrade your gearing to 7 or 8 speed. This makes setup easier.
Even if you buy a hub motor that is compatible with your bike’s gearing system, you can still run into compatibility issues. You may have to install a different sized cassette or freewheel to make everything fit. Hub motors tend to be wider than standard hubs. Some high gear count cassettes and freewheels may not fit because they’re too wide. You may also have to install a different derailleur and shifter if you change the number of gears significantly.
You can avoid having to deal with the gearing altogether by installing a front hub motor. This simplifies the conversion. When you use a front hub motor, you don’t have to worry about the gearing at all. The motor is completely separate.
You’ll also have to consider brake compatibility when choosing a hub motor. If your bike has disc brakes, you’ll need a hub motor that has mounting points on the side for the brake rotor. Most use a 6 bolt mount. In most cases, you can bolt your existing rotor onto the new hub motor.
One common issue with hub motors is that they place the disc rotor a couple of millimeters too far to the left. Ideally, the rotor mounting surface should be 15mm from the inner dropout at the rear and 10mm at the front.
Hub motors sometimes move the rotor a couple of millimeters to leave room for the wider hub. Unfortunately, this can cause the rotor to rub on the pads because it puts the rotor out of alignment with the brake caliper. This issue is common on generic hub motors. Brand name hub motors usually get the spacing right.
If you encounter this issue, you may have to adjust the caliper mount. In some cases, you can file down the mounting surface to move the caliper out a couple of millimeters. It may also be possible to increase the length of the slots to move the caliper.
You also have to make sure there is space between the side of the hub and rotor for the caliper to fit. Some larger hubs don’t leave much room for the caliper. Ideally, you want at least 18-20mm of clearance between the hub and rotor. Some motors only leave 14-15mm. This usually isn’t enough. The rotor will hit the motor.
If the spacing is tight, there are a few solutions. You can try using a more narrow caliper. Usually, mechanical disc brake calipers are more narrow than hydraulic disc brake calipers. The most low-profile models measure around 14mm wide.
Another option is to use a larger rotor and move the caliper further from the center of the rotor. This helps because most hub motors become more narrow toward the edges. This may require a caliper adapter.
Yet another option is to use spacers to move the rotor away from the hub. This makes the axle longer. You may have to spread your dropouts to make the wheel fit.
Rim brakes simplify things. If your bike uses rim brakes, you’ll just have to make sure your frame and rim brake calipers have enough clearance for the rim and tire you plan to run.
For more info, check out my guide to disc vs rim brakes.
Most hub motor conversion kits come with a complete wheel including the hub motor, spokes, and a rim. The complete wheel is already built and ready to install. If you choose a rear hub motor, the wheel may come with a freewheel or cassette attached.
This makes it much easier to install the motor. You don’t have to mess with building a wheel yourself or paying someone to build a wheel for you. Instead, you can simply swap out your old wheel for a new one with the hub motor already built in.
You need to choose a wheel that matches your bike’s wheel size. For example, if your bike has 700c wheels, you’ll need an ebike kit that comes with a 700c wheel. Many kits are available in a range of sizes. Common sizes include 20″, 24″, 26″ 650b, 700c, and 29″. Fat bike options are also available.
If you prefer, you can also buy the motor on its own and build it into your own wheel. This will be the better option if you prefer to use a particular type of rim or spokes.
Most hub motor complete wheels are factory built. The spokes may not be perfectly tensioned. Sometimes the wheels aren’t perfectly true. You might want to take the wheel to a bike shop and have it adjusted. This is much cheaper and simpler than building a whole wheel.
For more info, check out my guides to different wheels sizes: 700c Vs 650b wheels and 700c vs 26″ wheels.
Ease of Hub Motor Installation
Front hub motors are easier to install than rear hub motors. This is because you don’t have to worry about whether or not your cassette or freewheel and rear derailleur is compatible with the hub. The front hub motor is completely separate from the drivetrain. This simplifies things.
If you’re installing a rear hub motor on your existing bike, you can run into compatibility issues. When choosing a motor, you’ll need to take your bike’s gearing into account. Sometimes you’ll have to install a different cassette or freewheel to make everything fit. In some cases, this may require you to install new derailleurs and a new chain. This adds cost and makes the conversion more complicated. You’ll also have to adjust the derailleurs after installation so the chain doesn’t rub.
Of course, if you’re buying an ebike off the shelf, you don’t have to worry about installation. The bike will come from the factory with everything already installed.
Winner: Front hub motors are easier to install than rear hub motors. This is because there is no gearing in the front.
Who Should Choose a Front Hub Motor Ebike?
Front hub motor ebikes are the better choice for those who need good handling. The front motor better distributes the weight across both axles so the bike feels more balanced. This allows for better handling. The bike steers precisely and predictably. It feels a bit more natural to ride. It also makes the bike easier to ride. Beginner ebikers may appreciate this.
Those who are converting their existing bike into an ebike are sometimes better off with a front hub motor due to their greater compatibility and ease of installation. It’s often easier to find a front hub motor that will fit your bike because front dropouts are more standard. You also won’t have to worry about gearing when you install a front hub motor. If your frame is not compatible with a hub motor, you can swap out your fork to a model that is compatible. You can install a front hub motor on pretty much any bike.
Who Should Choose a Rear Hub Motor Ebike?
Rear hub motor ebikes are better for those who want to accelerate quickly and ride at higher speeds. Having the weight of the motor at the rear greatly improves traction. The weight of the motor and most of the weight of the rider sit on the rear wheel. The extra weight increases friction between the road and tire. This makes the tire less likely to lose grip and spin out. This allows you to get off the line quickly without your tire slipping. You can also corner a bit harder without losing grip.
If you want to run a large motor, you’re also better off with a rear hub drive. You can run a larger motor in the rear because the dropout spacing is wider and the rear dropouts are a bit more robust. A larger motor will fit and the dropouts can handle the extra power. If you want to use a motor with more than 750 watts of power, a rear hub motor ebike is the better choice.
Those who are concerned with safety are better off going with a rear hub motor ebike. The rear dropouts are much stronger and more durable than the front dropouts because they are designed to handle the force from the drivetrain. They are less likely to fail.
Final Thoughts About Front Vs Rear Hub Motor Ebikes
As we have seen, front and rear hub ebikes both have their own advantages and disadvantages. There isn’t really a clear winner here.
For most riders, a rear hub motor is preferable. The strength of the rear dropouts makes the system more durable. You don’t have to worry as much about frame wear or failure. Traction is also much better. This allows you to accelerate faster.
Front hub motors also have their place. They offer superior weight distribution. This makes the bike feel a bit more balanced and natural to ride. Rear tire flats are also easier to repair when the motor is in the front. Whichever style of ebike you choose, I hope this guide has helped you in making your decision.
Do you ride a front hub or rear hub motor ebike? Share your experience in the comments below!
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Monday 22nd of May 2023
Hubs are NOT interchangeable. Hub motors have different ways of communicating with the ebike controller. I have 2 ebike hubs with different hall sensors that only work with a specific controller.