Mid-drive vs hub electric bike motors – what’s the difference?February 3rd 2021
When you start looking for an electric bike, there’s one question that we get asked a lot – what’s the difference between a motor in the middle of an e-bike (mid-drive), and a motor set inside one of the wheels (hub), and which one is best for me?
OK, that’s technically two questions, but they’re both equally important. After all, understanding how each one helps you go further, faster and easier is one thing, but also getting to grips with which one could be right for you is another!
Here, we give you the essential information that you need to make an educated decision.
A mid-drive motor is positioned right in the middle of the e-bike, around what’s known as the bottom bracket area. Essentially, it sits inside the cranks (the arms on which you attach pedals), and it applies force directly to the mechanical drivetrain – the traditional collection of parts that make a bike move forwards.
In most cases, the drivetrain is made up of a traditional chain, chain rings and a cassette, which work together to drive the rear wheel and move you forward. Alternatively, you might be looking at a belt drive, which works in a very similar way to drive the rear wheel. Either way, a mid-drive motor adds to the pedalling force that you put into the pedals.
It can do this because there are sensors within the motor itself that measure your pedalling. The motor reads this data and responds by offering up extra power and applying it directly to the chain or belt, which has the effect of pushing you along with greater force.
Fundamentally, hub motors work in the same way as mid-drive motors – they generate assistance that adds to your pedalling force, making you accelerate faster and your ride easier.
The differences come in the way a hub motor gets its data and applies its assistance. Plus, the positioning of the motor changes things a bit too.
Rear hub motor
A rear hub motor is positioned – you guessed it – inside the rear wheel. This means that it’s very close to the mechanism that makes a bicycle move forward. When you pedal and the chain is pushing against the cassette, a rear hub motor measures the force at the rear wheel.
Once it calculates how much power you’re putting in, it then applies its own force directly to the rear wheel, propelling the wheel (and so the whole bike) forwards. Some hub motors, like those you’ll find on electric road bikes, are able to measure power lots of times every pedal stroke, making them very responsive. Others are simpler, measuring only a few times per stroke, but are usually cheaper and are seen on some hybrid or city-type e-bikes.
Front hub motor
Motors positioned in the front wheel are often considered simpler than rear wheel hub motors, because they’re not directly attached to the part of the bike that makes it ‘go’. This means that they don’t apply assistance to the drive wheel.
Instead, a front hub motor senses when it’s been pushed forward by the rear wheel. Because it’s directly attached to the front wheel, the motor then applies its assistance to that wheel, which means that you effectively get ‘pulled’ along as you continue to pedal and apply your power to the rear wheel.
Like other e-bike motors, some front wheel motors have a sensor that can work out the how much assistance to apply when it senses a certain amount of drive. Other, usually cheaper, models may deliver a set amount of assistance regardless of how hard you pedal.
Which is right for me?
One of the main advantages that a mid-drive motor has is in how directly attached it is to the drivetrain and your pedalling inputs. This gives the most direct response that you can get from a pedal-assist motor, effectively making the motor ideal for enthusiasts who want very responsive pedal assistance, and some hybrid e-bike riders that might use their e-bikes for multiple uses (e.g. the daily commute and weekend excursions).
Plus, mid-drive motors are sometimes able to deliver more peak assistance than hub motors, which makes them the mode of choice for electric mountain bikes, whose riders often need high levels of assistance to deal with really tough terrain.
The downside to this direct attachment is that you can experience increased drivetrain wear, because it has to handle the forces that you’re putting in through the pedals plus the forces that the motor delivers. In the medium to long term, this may mean that you need to replace some components more often as they wear.
Also, as these motors are often more powerful, to compensate you’ll sometimes have bigger batteries fitted to deliver a good range, but they may be a bit heavier and not fit as neatly inside the frame. However, specialist mountain bike brands will seek to integrate the battery as much as possible so that it doesn’t negatively affect the handling, while the integration design often allows easy removal.
On the other hand, hub motors are great for riders who don’t need the highest levels of performance – such as city cyclists – but still want the helping hand of a motor. They are often smaller (they need to fit inside a wheel!), can be lighter, and the batteries can be smaller and lighter too. This makes the whole e-bike lighter, and more svelte in its design.
Of course, this means that battery capacity can be less, potentially reducing range, and the motor itself – normally rated up to 250W like the vast majority of other e-bike motors in the UK and Europe – may not be able to deliver as much assistance per pedal stroke when turned onto its maximum setting.
That said, this means that hub motors are ideal solutions for those interested in urban commuting who often want a sleeker design for their e-bike, as well as road cycling enthusiasts wanting or needed a gentle helping hand that doesn’t dominate the ride, or take away from their bike’s more classic aesthetic appeal.
Front or rear hub motors?
If at this point a hub motor is your motor of choice, then you might need to choose between an e-bike with a front hub or rear hub motor.
If what you need is to get from A-B in your local area quickly and easily and for arguably the lowest cost, then a front hub motor is all you really need. However, the assistance you get can be more basic in delivery, while the front-driven wheel can take a little getting used to as you also steer through it.
A rear hub motor, thanks to being more directly connected to the traditional drive wheel, can deliver its assistance in a more reactive way, which means that when you pedal you’ll likely get a sharper response. Sometimes they’re more expensive than front hub motors, and replacing or servicing them can be a little trickier – but all motors require a specialist hand for servicing, which Pure Electric can expertly provide!