Ebikes motors – Hub drive verses mid drive?
One of the major differences in e bikes is where the motor is located, it can be in either the front or rear wheel hub, or in the bottom bracket between the pedal cranks which is called a mid drive. In this article I want to try and explain what the difference is between these setups and the pros and cons of each and how they feel different when you ride them.
What is a hub drive?
So firstly, what does it mean, hub drive or mid drive. A hub drive e bike has the motor built into either the front wheel or the rear wheel. If the bike has internal gears like the Nexus 3 speed then the motor will be in the front wheel as it is not possible to install the motor and the internal gears in the same wheel. If the bike has external (deraileur) gears then the motor can be in either front or rear wheel but is usually in the rear wheel. There is some difference between having the motor in the front or rear hub but for the purpose of this article the bike feels very similar to ride. Hub motors can be controlled by a sensor mounted on the crank of one of the pedals (this is called the pedal assist sensor, PAS) or the motor can be controlled by a torque sensor. The simple and cheapest setup uses the PAS which detects if the pedals are turning, the PAS does not care how fast the pedals turn or how much effort you are placing on the pedals, it just wants to see if the pedal is rotating.
The display on the handlebars usually has up to 5 power level settings (1 to 5) which basically provide 20%, 40% …up to 100% of the maximum power (250W for street legal e bikes in Queensland). When you select a power level and the PAS sensor detects the pedals are turning then the motor runs at whatever power level you have selected, regardless of how fast or slow you are pedalling.
What is a Mid Drive?
It is called a mid drive because it is in the “middle” of the bike, built into the frame between the pedal cranks. These motors drive the rear wheel using the chain , just the same as you do when you pedal. Instead of using just one sensor to detect if the pedals are turning (like the PAS) the mid drive using a combination of up to three sensors, the speed the bike is travelling, the torque or force that you are applying to the pedals and the speed that you are turning the pedals (cadence). These 3 inputs are then used to generate the assistance form the motor based on the level you have selected on the display and the BIG difference to the hub drive control is that the motor responds to how much force you are applying to the pedals, not just are the pedals rotating.
So how does the hub drive and mid drive impact on various things about the bike?
Lets start with Price.
Which one costs more?
In our shop the mid drive is always more expensive than the hub drive bikes. This is due firstly to the cost of the motor, a mid drive motor is more complicated and more expensive to build than a hub drive and the bike frame has to be designed to accommodate the mid drive motor whereas with a hub drive the bike frame is a standard frame so manufacturing costs are less. Also, if you are already paying more for the mid drive then the rest of the bikes specification normally goes up as well so you end up getting hydraulic front and rear disc brakes, better spec gears and other features. Overall this means that a mid drive bike might be $2000 more than a hub drive.
What about the weight distribution between the two?
Depending on where the battery is located in a hub drive bike you may end up with a lot of weight at the back with a rear wheel hub drive and the battery located on the rear rack. If the motor is in the front wheel and the battery is on the downtube then you end up with a lot of weight at the front of the bike. With a mid drive the weight of the motor is nice and low in the middle of the bike which feels more like a mechanical bike and usually battery is located either on the down tube or behind the seat post so most of the extra weight associated with the electrics is kept in the centre of the bike which makes the bike feel more traditional in its handling.
Yes but does one setup feel any different to the other when you ride them?
The short answer is yes, depending on how you want to ride the bike. With the hub drive bike you just need to get the pedals turning, you do not need to put in much effort, just get those pedals turning and the power will come on at the level you selected. For riders who may have muscle fatigue or knee joint issues where they cannot put a lot of force on the pedals they can use “walk assist” button to get the bike moving without pedalling and then start pedalling once the bike is moving which puts very little force on your joints. Others might be happy to just cruise along, pedalling slowly and travelling at up to 25kpm on the flat when in power level 5.
On the other hand, if you are the type of rider that wants to feel as though they are riding the bike and applying pressure to the pedals then the mid drive feels like a mechanical bike but with more power. As you push harder on the pedals the bike gives you more power (speed) and as you ease off the bike slows down. With a hub drive the bike DOES NOT slow down as you pedal slower. For some riders on a hub drive this can be disconcerting if they are going around a corner and start pedalling half way round and the power kicks in.
The same thing can happen when riding up a hill, if you are in level 5 and powering up the hill as you crest the top of the hill and come onto the flat you might slow down your pedalling but the hub drive will still give you the maximum power and speed up on the flat section.
The mid drive bikes offer a more intuitive, natural ride feel like riding a traditional bike. They also allow the rider to maintain a higher average speed up hills but do require the rider to put in more effort.
So all in all, the choice between a hub drive verses a mid drive comes down to a number of factors, how much you want to spend, how you want to feel when you ride the bike, what type of riding you will be doing and the terrain that you will be riding in.
The best way to make an informed decision is to come into the shop and try our range of hub drives and mid drive bikes and see how they feel for yourself.