Mid Drive Vs. Hub Drive | Which motor for e-bikes is better?

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Mid Drive vs Hub Drive?

We’ll start this like Fincher’s Fight Club, the end at the beginning and then explain why.
Mid drive vs hub drive?

Mid drive takes the cake. I was going to say that it depends on your use, but that’d be too cliché.  When you really break it down, the mid drive is a clear winner. I’ve included a table below for your convenience but if you want to really understand why, continue reading below.

Mid Drive

Hub Drive

ProsConsProsCons
Greater torque = better hill climbingMore ExpensiveRelatively cheaper than mid drivesHeavy and uneven weight distribution (especially with front hub)
Overall better performanceMore wear and tear on drive-trainCan DIY with large range of ‘off the shelf’ motors.Torque arm required for high powered hub motors (front hub)
Low and centred weight distributionNot many retrofit options. Mostly proprietary motors on complete e-bikes.AWD system (front hub)Issues with climbing steep terrain
Utilises the gears, thus providing higher top speedsLess strain on the drivetrainLimited top speed

 



How the Journey Begins?

It’s a question that has been around since the dawn of e-bikes. You get an electric bike for the first time and get addicted to the boost. Three weeks after riding you’re on the hunt for more power and looking at other motors. It creeps into every e-bike rider’s mind and eventually you find yourself up at 3am reading endless threads on forums and watching YouTube videos on what’s better.
No? Just me?
Well I’ll make it easy for everybody and break it down.

Let’s begin with a little lesson on what each type of motor is to understand why mid drives are better.

Hub Drives

Hub driven bikes are commonly powered by DC motors, typically brushless as they; perform better, are more reliable, and quieter (than brushed). If you want to know how a DC motor works or the difference between a brushed and brushless DC motor, Youtube can help you with that. Find one with animations as they help illustrate how they work with more details.

Okay watched the video?

So back at it. You’ll find a typical torque and power curve below for a DC motor.

[Credit: EBN]

With DC motors, torque is always maximum at zero speed which is called the stall torque. As you can see above, the motor’s torque will drop in a linear fashion with speed/rpm. The theoretical power curve will be a parabola shape and peak somewhere in the middle. If you read my bike reviews, you’ll know that I test and dyno the e-bikes when possible. Here’s a plot of the Fat-E Mini below.

You can see that it resembles the theoretical plot quite well. There are some irregularities due to real world effects such as friction, efficiency and what not, but it seems fairly accurate. What’s important to look at here is the area under the curve, not the peak torque or power. A car or mechanical enthusiast will always tell you that a machine with more area under the curve will outperform one that has less area – especially if they produce identical peak numbers. Just remember this as we get into mid drives.



Mid Drives

With mid drives, they’re almost identical to hub motors however mounted at the bottom bracket of the bike. It directly connects to your cranks and gears. Because of this, you get a better power/torque curve. Imagine the hub drive dyno, but then add a plot for each gear like this:

Dyno plot completed for the Dillenger Hunter Off Road. Testing 2nd, 5th and 8th gear.

Yeah a little crazy, but it’s pretty much the hub drive dyno for each gear. The curve stretches out with each higher gear. Do we remember what was said about power/torque plots? It’s the area underneath the curve that really shows the performance of a machine, especially when they’re rated at the same peak power/torque.

Let’s just assume that the peak power numbers for the Hunter are identical to that of the Fat-E Mini. Comparing the characteristics of each plot, you have the mini with one power curve whereas the hunter has multiple power curves (as many as the gears it’s fitted with). These multiple power curves are essentially combined which obviously would sum up to a large area – greater than a hub drive power plot (not always true, but typically). So in terms of performance, the mid drive is a clear winner.

Power and torque Performance? Mid Drive

How do they compare in handling?

As we should know by now the mid drive is installed on the bottom bracket with the battery/controller installed on the down tube. This keeps the bike’s centre of the gravity very low and centred. With a hub drive, the centre of gravity is generally a little higher than the mid drive by offset – either to the front or rear. Using my next level professional photoshop skills, I’ve compiled a diagram below where the black and white circle label symbolises the centre of mass.

Depending on the wheel size, the hub motor could sit either higher or at the same height as a mid drive would. This results in the centre of gravity being somewhat similar in terms of height, however the front or rear hub will shift the weight, either towards the front or rear. This will affect handling, and is especially the case with the front hub. Having a 3kg wheel that you turn with, will greatly impair the handling of a bike.

Handling? Mid drive

How does the mid drive stack up against the hub drive with price, maintenance and other things?

Frankly the mid drives trumps the hub drive in almost everything but price. They are more costly and when something does go wrong, they are more expensive to fix than hub motors. Another thing to consider is that hub motors are readily available with many options on the market. These motors are also easy to install and allow retrofitting. Mid drives on the other hand are a different story.

With Bosch, Shimano and Yamaha (just to name a few) producing complex high end mid drive motors, it makes it difficult, close to impossible to fit it to your current bike. Unless you’re a frabricator who can make a custom frame, it’s most unlikely for you to be able to buy a Bosch mid drive on a weekend and fit it on your daily commuter in one arvo. There is Bafang who provide mid drive kits that fit onto the bottom bracket but even with that said, hub motors are more readily available and easier to install.

Cost and couple of other things that no one really cares about? Hub drive

Conclusion

There you have it folks, we’ve come to a full circle with mid drives taking the win in this fight. Hopefully you understand from a deeper level why mid drives are better, and share this with your friends and fellow riders! Remember the first rule of E-Biking Now is to talk about E-Biking Now.



4 COMMENTS

  1. Hub motors are almost useless. The basic problem is that (very roughly) motor torque is proportional to weight. So for the sort of torque you want at the wheel you NEED a reduction gear – with hub motors you will need two reduction gears once for each wheel. Everybody starts off thinking “hub motors are cool” – but nobody end up using them because they are usless.

    • Heya Jake,
      Are you from FLX electric bikes?
      Oh really? I didn’t know that. Cheers for explaining that for us.
      I guess that cements mid drive motors in this debate. The only thing that hub drives do have going for them is maybe 2 things; it’s simpler and cheaper. But these are changing with the progression of eBike kits. Mid drives are getting cheaper and simpler.
      – Eric

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