With more and more electric bikes on the market in Australia, we're seeing more examples of the various places a motor can be added to a bicycle. This article is about the advantages or otherwise of the three main motor placements on an electric bike. It is about 'complete electric bicycles', as opposed to electric bike conversion kits.
Spoiler alert - there's no particular 'absolute best' type of motor. Instead, each motor type is suited to a different type of bike and riding style.
Understanding Hub Motors
Hub motors are a cornerstone of modern electric bikes, offering a blend of efficiency and reliability that appeals to both casual riders and e-bike enthusiasts. These motors are ingeniously integrated into the hub of the wheel, where they use electricity to generate torque. This torque is then transmitted directly to the wheel, propelling the bike forward with smooth, consistent power. Available in various power ratings and configurations, hub motors cater to a wide range of applications, from daily commuting to recreational rides and even off-road adventures. Their straightforward design and dependable performance make them a popular choice for those looking to enhance their cycling experience with electric assistance.
Hub Motor Types
When it comes to hub motors, there are two primary types to consider: front hub motors and rear hub motors. Front hub motors are positioned at the front wheel, providing a straightforward and low-maintenance solution that balances the bike by distributing the motor’s weight forward. Rear hub motors, on the other hand, are located at the rear wheel, offering enhanced traction and a more natural riding feel, especially on challenging terrains. Additionally, there’s the mid-drive motor, which is situated near the pedals and drives the bike by pulling on the chain, similar to how pedaling power works. Each type of motor has its unique set of advantages and disadvantages, which we’ll explore in more detail in the following sections.
Front Hub Motor - the sensible option
This is one of the simplest implementations of the electric bike. The motor is inside the hub of the front wheel, creating a front wheel drive system that turns the wheel over, making the bike move.
Advantages: Simple is good. This is very low maintenance as it shares the strain on the bike between the front wheel (motor power) and rear wheel (human power and rider weight). It also physically separates the motor system from the rest of the bicycle parts, making your bike easier to service and spare parts more aligned with conventional bike parts. It allows any type of gearing in the rear wheel, such as internal hub gears. No matter where the battery goes, you’ll end up with a well balanced and very stable bike.
Disadvantages: Front end of the bicycle becomes heavier, reducing choice of front forks and making it a little harder to lift up a curb. Traction is an issue on very steep tracks with loose surface. Quick release front wheel not an option. Above a certain power level, front hub motor becomes unviable for various reasons. However, this article is not interested in e-bikes of that level of power and speed, it is focused on legal electric bikes.
Best suits City Riders. So what kind of rider or what kind of bike best matches up with the advantages on offer? A low maintenance and simple e-bike with good balance and internal hub gears is going to best suit ‘everyday riders’ who ride to get around the city with the occasional rail trail and just want a comfortable, safe and reliable e-bike. These riders don’t suffer much from the disadvantages either, being mainly on paved roads. For this person, some of the disadvantages are actually advantages - no quick release front wheel means less theft risk. And a heavy front end on a bike with ‘upright’ seating position isn’t a problem while riding and actually adds to stability. Another ‘sweet spot’ for these e-bikes is for commercial and fleet use, when predictable maintenance requirements and costs are paramount to the fleet’s success.
Least Suits MTB Riders. Which kind of rider would not benefit from these advantages and would suffer most from its disadvantages? A mountain-biker. They are always riding on loose surfaces, their bikes are not ‘upright’, choice of high tech front forks is essential and a heavy front end when jumping over tree-roots etc isn’t going to work. Low maintenance doesn’t appeal to them either, they won’t want internal hub gears and with the rates of crashing their bikes, a trip to the shop every now and then is normal.
On the fence - Touring Riders. Electric bike touring riders are in between. They will encounter a variety of riding conditions where a heavy front end might be inconvenient. On the other hand, low maintenance and simple is paramount for long distance riders. The decision will be based on the likely terrain and will be some sort of compromise.
Rear Hub Motor - the Fun option
In reality, there isn’t a huge difference between a front hub or rear hub motor electric bicycle. Both have similar performance, the motor has similar design constraints and both are very efficient in propelling the bicycle without a drive chain (direct to the spokes). However, a rear wheel hub motor can present challenges, particularly when dealing with flat tires, as the motor's placement can complicate repairs. The real consideration for the buyer is a trade-off in maintenance vs the feel of the ride.
Above a certain power level, a rear hub motor is the easiest way to pack in a lot of power relatively safely without damaging the frame or causing the bike to slide out around corners.
Advantages - Light and maneuverable front end, allowing any type of front fork. All your weight is on the motor, giving it maximum traction even in adverse conditions. Aesthetic advantage of being able to conceal the motor among the gears, panniers bags etc. Even when the same hub is used, noise levels are lower on a rear hub, due to the extra weight on the wheel minimising vibrations and resonance through other parts.
Disadvantages - Choice of pedalling gears are restricted. In general, derailleur gears are the only option, and not internal hub gears. Rear wheel and spokes under enormous stress - your weight, your pedalling power, the motor’s power, the motor’s weight and even the dimension of the motor make for a more difficult wheel build than a conventional bicycle hub. It is not unusual for electric bikes with rear hub motors to break spokes regularly.
Best Suits: Riders who will often go off-road on steep/loose tracks. Also city riders who are happy to prioritise the feel of the ride and accept higher maintenance on the rear wheel and weren’t going to choose internal hub gears in any case. It is best suited on high-end e-bikes where the rear wheels are built with high quality components and to a high standard of manufacture.
Least Suits: Any owner for whom maintenance is a priority including fleet operators. The combination of more motor wheel maintenance, plus no option for internal hub gears will mean overall increased maintenance. Note that rear wheel drive bikes are easier to sell in general, so you see more of them. Unfortunately this means there are a lot of cheaper electric bikes with rear hub motors where it’s only a matter of time before the spokes start breaking and expensive and lengthy work is required. The heavier the motor and the heavier the rider, the more of a problem it will be.
Hub Motor Placement and Traction
The placement of a hub motor significantly influences the bike’s traction and overall performance. Rear hub motors are particularly effective in providing superior traction, especially on steep or slippery surfaces. This is because the combined weight of the rider and the motor is concentrated at the rear wheel, enhancing grip and stability. In contrast, front hub motors can sometimes struggle with traction control on challenging terrains due to the lighter load on the front wheel. However, advancements in technology, such as higher voltage systems and smaller wheel sizes, can mitigate some of these traction issues, making front hub motors a viable option for many riders.
Weight and Balance
Weight distribution is a crucial factor when choosing between a front or rear hub motor for your electric bicycle. A front hub motor can help balance the bike by spreading the weight forward, which can be particularly beneficial in preventing the front wheel from lifting during acceleration. This balanced weight distribution can enhance the overall stability and handling of the bike. On the other hand, rear hub motors can sometimes lead to weight distribution challenges, especially if the battery is also mounted towards the rear. Despite this, rear hub motors offer better traction and smoother acceleration, making them a preferred choice for riders who prioritize performance on varied terrains.
Mid-Drive Motors - the 'have it all (almost)' option
Mid-drive motor systems on electric bikes from Bosch and Shimanoare now much more common in the Australian market. This option is quite different to the hub motor setup. The mid-drive motor pulls on the chain, just as your pedalling power does. This then turns the rear wheel and away you go. The motor's drive goes through the bicycles gears, so the motor is effectively geared too.
Advantages: Allows both wheels to be 'normal' bicycle wheels, giving all the available options of quick release, internal hub gears etc. Front forks can be any type and both front and rear end of bike is kept light. Centre of gravity is low and the whole e-bike is usually a little lighter too. The drive is via the rear wheel, so traction is not an issue. Rear wheel spokes are not stressed as much as on a rear hub motor setup because the motor's weight is not back there and the wheel build is not affected. Motor is geared, so going slow and steady up very steep hills is achievable.
Disadvantages: More complicated system, so motors are usually more expensive and the proliferation of sensors in the bike adds to possible failure modes. The drive-chain is under increased stress (human power + motor power through the one chain), so the chain, gears and rear hub will need to be maintained and replaced more frequently.
Grey Area: There's a lot of aspects on a mid-drive e-bike that are either advantages or disadvantages, depending on what you want from an electric bike.
- Motor replaces bottom bracket, providing an opportunity to measure the rider's effort on the pedals and tuning the electric drive system to respond accordingly, making for a ride that feels more like riding a normal bike. This also means it forces you to do a bit more work
- The motor is going through the gears, so you can change gear to keep the motor in its most efficient mode. But this also means you have to be in the right gear for the motor whenever you change speed/hills. More to do/learn
- Many of these bikes are coming from Europe. This gives access to e-bikes of a higher standard of manufacture and finish than what we are often used to down under. This also means more scarce or expensive spare parts and usually the bikes are speed limited to 25kph and they usually don't have a throttle option.
Best Suits: Hands down the best system for expert MTB riding. Rear wheel traction but with good centre of gravity, lightweight wheels and any suspension option is possible. Also a good compromise for electric bicycle touring. Has rear drive traction, not too many rear spoke problems, often easier to ride unassisted than a hub motor e-bike. Not as low maintenance as a front hub motor but by carrying some spare chains with you and careful cleaning/maintenance it is completely manageable.
Installation and Maintenance
Installing and maintaining hub motors can vary in complexity depending on whether you choose a front or rear hub motor. Front hub motors are generally easier to install, as they do not require adjustments to the bike’s drivetrain components like the freewheel or derailleur. This simplicity makes them an attractive option for those looking for a straightforward electric bike conversion. Rear hub motors, however, can be more challenging to install due to the need for precise alignment and integration with the bike’s existing gears. Regardless of the type, regular maintenance is essential to ensure optimal performance and safety. This includes routine checks and adjustments to the brakes and drivetrain to keep your electric bike running smoothly.
By understanding these aspects, you can make a more informed decision about which type of hub motor or mid drive motor best suits your riding style and maintenance preferences.