Here at Bicycle Junction we carry electric bikes that use high quality electric motor systems, from companies such as Shimano and Bosch. Bosch makes some of the most powerful motors for ebikes that are available and were one of the initial pioneers in this field. Both these companies only make mid-drive electric systems, which we will outline the reasons for below.
Previously, hub-driven motor systems were the standard, as they were the first electric bike systems to hit the road. Nowadays, as a result of vast development of mid drive systems and their intrinsic benefits, they have been largely phased out by most bicycle companies. A mid drive system has the advantage of driving through the bicycle gears, which allows for a greater torque control and speed range.
The problem with hub drive motors is that they don't give you the full assistance on the steepest of hills. The reason for this is because there's no gearing, and electric motors like to run at a certain rpm. In the mid drives, you can maintain the right rpm by using your gears so that you can go slowly up a hill, with full assistance. With a hub drive, because it's attached directly to the wheel and to the road, as the bike slows down, the motor also slows down. When you get down to low speeds, it's going to stop giving you the full assistance because the motor is trying to work outside of its limits. If it keeps trying to give you all that power, it's going to burn out the motor. This is an obvious issue since when you're climbing the steepest hills, you're going to be going the slowest, and you'll be needing the assistance the most. It's like having a car that only has a third gear, you can't quite go 100km/h and you're really going to struggle going slowly up a steep hill. Hub drives aim to work within the middle speed range, but are not very efficient at high speed, or going to work very well uphill at low speeds either.
Beyond the pure mechanical benefits of how mid-drive systems work, there are lots of other practical benefits that are available to the rider, such as them being more responsive to rider input, with more assistance control. The motor weight is also kept central in the frame, improving weight distribution which makes handling of the bike better. Mid drives also suit bikes with internal hub gears and all wheel sizes, as they do not interfere or depend on the wheels whatsoever.
Now, as with any bike, as we suggest to our customers, you always need to look for the established brands of motor. And the reason is that we've seen a lot of bikes come through that simply don't have local support. We deal with Bosch and Shimano, Bosch and Shimano have their own support networks in New Zealand, with all the parts and all of the diagnostic tools, and all of the knowledge support for any Bosch or Shimano dealer in the countries. That means if you buy, for example, a Bosch bike from us, but you live elsewhere in the country, you can go into your local Bosch dealer, and they can sort it for you. If you've bought something from a generic supplier and you need only the support, it's going to be more difficult for you. Plus, there's a lot of bikes and motor brands that don't have diagnostic tools to go with them. If you don't have diagnostic tools, then the only way a mechanic can find what's wrong with the problem is by replacing parts until the problem stops. That's very costly, both in money but also in time. We also know that Bosch and Shimano will continue to support the bikes years into the future. So you will be able to replace batteries years into the future motors, whatever comes up, they will continue to be supported. There's no guarantee with other brands, if someone's bringing in some cheap electric bikes that that company is going to be around in a couple of years, or that there's going to be New Zealand support in a couple of years.
Our only exception
As with all rules, there are exceptions. The image above is of the new Brompton Electric, which is the only hub-driven bike we will be carrying this year, as in this specific model, the use of a hub-driven motor makes sense.
Firstly, it's not meant to be a fully-powered electric bike like the majority of bikes we carry are. Instead it's lightweight design to provide a little assistance, to make getting where you need to be that little bit easier. The fact this bike uses small 16" wheels works to its advantage, as it means that the motor is able to keep a higher RPM than a bike with full sized wheels, meaning that the motor is more likely to function properly even when climbing. But most importantly for this bike, is the practicality of this system on a Brompton. Keeping in line with Brompton design philosophy, this bike had to be easily foldable, and light enough to carry. Due to its size, a mid drive motor would have interfered with the folding so was unable to be used in this situation. Another unique feature of the Brompton Electric is it's detachable battery pack, which allows the battery to be carried on your back, leaving only the motor attached to the bike. This makes the bike lighter and easier to carry, which is a crucial part of what makes Bromptons so popular.
Another significant thing to consider is that Brompton as a company has been around for a very long time, and has very high standards for the quality of their products. This means that you shouldn't run into as many issues as you would with a cheaper hub-driven system, and that Brompton will have spare parts and diagnostic tools well into the future, meaning that this bike will be able to last you well into the future. For these reasons, the use of a hub-driven motor on the Brompton Electric bike is a hub drive bike we're happy to carry.
If you're after some further reading on the topic, Bosch even have their own article on hub vs mid drive, which you can read here.