As you know, electric bikes have an electric motor, or motors, that help you with riding.
The ones without motor they call bicycles. Perhaps one day e-bikes will be so common that non-ebikes will be called manual bikes. Ha (with luck not Analogue bikes).
There are only a couple of spots an electric motor can practically go on a bike; in one or both wheel hubs or in the middle where the crank goes.
This article will give you some things to consider when looking at buying a crank-drive, or mid-drive, ebike.
It won’t be the complete story since there are many variations of bike design, motor, controller and battery setup in the market place.
We have four mid-drive bikes in the shop at the moment.
The ladies Gepida, the hardtail E-motion REVO 650B, the German Kalkhoff and the German Flyer road bikes.
What are they like to ride?
If you’ve never ridden an electric bike, then they’ll feel like they are rushing downhill. That’s the general feeling of an electric bike since they are all designed to sense pedal rotation, and some also sense torque ie how hard you are pedalling, and they apply power proportional to this to assist.
If you’ve ridden ebikes with the motors in the front or rear wheel, you probably won’t notice much difference.
You’re probably reading this though to decide which way to go, so let’s get into more of a side by side comparison of the two systems.
Before we go further then consider this when doing the comparison; are you comparing apples with apples, or apples with oranges?
What I mean by this is that all motors are designed with a different purpose.
Road bikes tend to be designed for efficiency at higher speeds and longer range.
Off-road bikes tend to designed for slower speeds and higher torque. Efficiency isn’t as much of a consideration in their design.
So if the road bike you ride feels sluggish compared to the mountain bike, that might be why.
Hub vs Mid-drive
As I said the main obvious difference between the two motors is their location, but their location also determines their internal configuration.
A hub drive motor lives in the middle of your wheel.
This means it has no choice as to what speed it turns since your wheel is basically an extension of the rotor in the motor (in an electric motor there is a stator, which stays still, and a rotor, which rotates).
This means if you are going slow, then the motor will be rotating slowly. Most electric motors are not as good at pushing you if they are going slow.
Just like a car engine, they have a preferred revolution speed where they use the electricity from your battery more efficiently.
A mid-drive motor not only often has internal gearing, but it also drives the back wheel through a bike gearbox, ie your front and rear clusters, derailleur etcetera.
This means the motor’s rotation speed is relatively independent of the back wheel. This means that it can be a more efficient motor.
Most people want to know which type of motor lets them go further. In our experiments, both configurations of motor were about the same. Research indicates both motors are equally efficient, but that is because the definition of efficient keeps changing.
Sometimes the efficiency referred to is how well the motor turns electric power into propulsive power purely in the motor. This does not take into account how the bike is geared or configured on the bike. Nor how the rider might ride it, nor the terrain/style of bike. If you talk purely about the motor, the mid-drive motors seem to be more electrically efficient than the hub motors.
As far as range goes though, we have not been able to tell a significant difference.
Here is a picture of the inside of a Bosch Performance Line electric motor (thanks to https://www.e-bikeshop.co.uk)
Notice from the picture that the Bosch motor has a motor, gearbox and controller all inside the alloy case (we here at Tas Electric Vehicles will be the Bosch authorised repair station for Tasmania soon. Stay tuned for the news).
But a more efficient motor does not automatically mean a more efficient bike. The fact the mid-drives have internal gears and then a set of external bike gears to apply their power through, means there a losses in the system before the back wheel gets turned.
This means a hub motor is more efficient at getting the rotational energy it produces to the ground. Additionally, some hub motors are starting to have internal gearing.
To be accurate, all hub motors have some gearing, like in the picture, but the overall speed of the motor is governed by the currently applied, not the internal gearing.
This hub motor has no gearing to change its speed.
(Some older hub motors are direct drive and have no planetary gearing system in them at all. You won’t see those in new bikes these days generally.)
You might think this would make a hub motor heavier, but gearing means the hub motor can be smaller and rotate faster, to produce the same result. This often makes the hub motor lighter since making an electric motor bigger usually means larger magnets and coils. Gearing on the other hand is often nylon and so weighs a lot less to get the same result.
Another factor to consider is that a hub drive motor drives the wheel directly because it is part of the wheel, this means that chains and gearing are not a factor in the wear and tear of the motor.
Crank/mid-drive configuration means the motor applies its power through the chain and gearing system of the bike.
This isn’t an automatic issue in Australia because all our bikes are quite low powered by law, but if you decide to fit a larger motor to an existing mid-drive bike, then you may experience increased wear and on the chain and gearing.
(In Tasmania, if the bike is over 200 Watts at the drive wheel, it is considered a motor vehicle and must be registered and fitted with a compliance plate. Less than that they consider to be ‘pedelec’ vehicles. You can read all this here at the Government link which was valid at the time of this post. Link goes here in case you want to cut and paste. http://www.transport.tas.gov.au/__data/assets/pdf_file/0015/141117/Power-assisted_pedal_cycles_-_Information_Sheet_-_Dec_2016.pdf)
There is more to consider. How about Gravity.
Gravity and Weight Distribution
If you plan to motor along flat bitumen roads, then the main thing to consider is overall weight, so check the specifications of any bike you are considering.
If you plan to use the bike off road though, then where the weight sits changes the centre of gravity for the bike and also, if you are after rear suspension, then if affects sprung vs unsprung weight.
Additionally, mid-drive motors on some ebikes hang down a bit so ground clearance can be an issue.
Mid-drive bikes have the weight in the centre so a mid-drive electric bike should handle the same as any slightly heavy mountain bike (most e-bikes swing in at around the 20kg ish mark, so not a light bike).
Since mid-drive bikes have absolutely standard front and rear ends, front forks, rear suspension, gearing and derailleurs, hydraulic brakes etcetera can all be standard bike kit.
But, as mentioned, the motor may hang down a bit. Also the angle of the motor in the frame can be a factor.
Notice the Bosch motor on the road bike was not angled to consider obstacles.
The Brose motor on the E-motion REVO 650B was specifically angled to ride over obstacles.
You can see the difference in motor angle and placement when comparing the Gepida ladies road bike to the REVO Emotion 650B offroad bike.
Suspension wise, having a motor in the rear wheel on a dual suspension ebike means that the rear wheel is now heavier. This means it will respond to bumps more slowly since there is more of it to go up and down.
Depending on the terrain and type of rider you are, this can be both a good thing and a bad thing. The main thing is that it is in your head to consider.
Below are two more of our road bikes. Both of these bikes are driven by the Bosch mid-drive motors.
Price and maintenance factors.
There are many mid-drive motors on the market. At the moment in the shop we only have Bosch and Brose motors.
We haven’t seen any significant pro or con to either. They are both high quality German made motors. It is likely that German engineering will make them a pricey item to repair if they get damaged and we haven’t found anywhere that supplies parts for the Bosch motor direct to the public for a DIY fix. To get around this we will be training up to be the Bosch repair place for Tasmania (another reason it is good to buy off a dealer rather than directly from the Internet. Just saying. 😉 )
As buyers we’ve noticed that the Bosch is a more expensive motor than the Brose, so the gear on the Bosch isn’t always the same standard when looking at the same pricepoint of bike, but on ebikes costing many thousands of dollars, no bike has what you’d call cheap components, so we don’t see it as that much of an issue.
Mid-drive motors tend to have the motor and controller all sealed up inside the one box, so if it goes wrong, you need to get the lot fixed.
Not all hub motors are like that. Some have the controller outside the motor so that the motor can be bigger and run hotter. This means hub setups tend to be easier to fix.
The negative of a hub motor is that it is part of your wheel so standard spokes won’t fit. It also means that if the wheel with the hub is damaged, you can’t just drop in a spare wheel.
In both cases though you can see that the issue is mainly with the type of thing that goes wrong. Motor vs wheel issues.
Mid-drive vs hub drive is much of a muchness.
They have similar range and efficiency as far as we can tell.
The main factor will be the type of bike you’re buying.
Off-road use means a torquier motor and considerations with the suspension and centre of gravity.
On-road use means speed and range.
Cost wise for repair etcetera it all depends on what goes wrong. So far hub systems seems to be easier to DIY repair than the sealed mid-drive systems.
If you won’t plan to every repair your bike though, then that doesn’t really matter.
If you’ve got any questions or thoughts about what wasn’t covered in this article, please comment below and we may update the article.
(If you want to sell us your SEO services, or web development services, or new shoes etc using the comment box below will drop you straight into the SPAM blackhole, so don’t even bother.)