We have already hinted many times at automatic gear shifting systems for ebikes: nowadays it is a mature technology, ready to invade the market, and well worth an in-depth article.
Difference between automatic gears and electronic gears
First of all, make sure not to mix automatic gear shifting systems with another technology which is more and more widespread: electronic gears.
- An electronic gear shifting system, used more and more on racing bikes and in the phase of being introduced to the mtb world, is just a normal gear system actuated by electric impulses which command a small electric motor (instead of the traditional mechanical levers which regulate the tension of a steel cable, and therefore the position of the derailleur). It is still up to the cyclist to decide when to change gear; just, instead of pulling a mechanical lever, she presses a button. The more widespread system is the Shimano XTR Di2
- With an automatic gear shifting system the cyclist must only thing about pedalling. It is the system itself which “decides” when it is time to change gear (and actually does it), based on the speed of the bike and/or the pedalling cadence
Advantages of ebikes with automatic gear shifting systems
Why can it be advantegeous to use an ebike with automatic gears? There are many reasons:
- comfort: it’s just one thing less to worry about. You don’t have to remember which gear you are using; you don’t have to worry about avoiding crossing the chain; you don’t have to actuate the levers on the handlebars when you just want to pedal and enjoy your journey. It is true that an expert cycling can do these things almost unconsciously and automatically, but there are many people for whom selecting the right gear is not that easy. Moreover, in an urban environment, when you often have to stop and restart, you have to change gears very frequently, which is annoying for everybody, whether expert or not. Pedalling with the right gear, and therefore with the right cadence, also helps to perform a more regular effort.
- safety: it has happened to anybody at least once: you proceed at a high speed, a traffic light turns red, and you forget to downshift as you stop. When you start again the hard gear forces you to push on the pedal with the whole weight of your body, and the bike wobbles a bit on one side, exposing you to the risk of being hit by other vehicles. It happens with “normal” bikes, but also with ebikes, especially the ones fitted with a simple pedalling sensor, which leaves the task of starting entirely to the cyclist (ebikes with a torque sensor behave differently, as you can read here). With an automatic gear shifting systems (many of which are also able to downshift when the ebike is stopped), this is not a problem anymore. Moreover, if you don’t have to worry about changing gears you can concentrate more on the urban jungle around you.
- motor efficiency: almost all the automatic gear shifting systems are made with rear hub gears. Therefore, the motor is almost always on the bottom bracket (that is, between the pedals), and therefore acts directly on the bike transmission. Motors of this kind, in order to work efficiently, should be used at 60 to 80 RPMs. An ebike with automatic gears helps the cyclist to stay within that optimal range; a motor which works in an efficient way is less demanding of the transmission and consumes less, helping you go further with each charge.
An ebike with an automatic gear shifting system is not an option which can be valid for anybody. In some situations there can be more disadvantages than advantages. Let’s consider a few use cases:
- Urban use: this is where you can get the most benefit from an automatic gear shifting system. It’s in the city that you have to change gear more often, and not having to think about it helps you to concentrate on your route and on the possible risks of the urban jungle
- Cycle tourism: the advantages of an automatic gear start to be less important, and the disadvantages start to emerge. Let’s think about a classic cycle tourism scenario, where you are pedalling away for long stretches on a mostly flat route, maybe along a river in Europe: you won’t have to change gear that often. Automatic gears shifting systems can weigh more than normal gears, and this can be a small disadvantage in the case of a trekking use with dozens of miles of travelling each day. More important, in case of a mechanical failure, it will be almost impossible to find someone able to intervene on an automatic gear, whilst any cycle workshop is able to repair (or replace) a common derailleur
- Sport use: here all the limits of automatic gears come to the surface. Those who pedal in a sportive way (whether on road racing bikes or MTBs) want to keep the maximum control on the gear to use. Moreover, sometimes you need to anticipate the moment of shifting gear based on the path ahead, something that an automatic system will never be able to do (at least in the foreseeable future): think about a mountain biker who selects a low gear before he actually needs it, in order to avoid stressing the transmission. An automatic system can not know that in 20 meters will begin a 20% uphill sector, and therefore you should change gear now.
Available automatic gear shifting systems for ebikes
As already mentioned, automatic gear systems are basically an evolution of rear hub gears. This is nowadays a settled and tested technology at least in the simplest variants. Here is a quick look at the various kinds of automatic gears now available on the market, starting from the “dumbest” to the more “clever”:
- two-speed Sram Automatix: it is a simple rear hub gear with two gears. The higest gear is selected automatically once the ebike reaches a certain speed. It can be used on a standard chain transmission, however only with a fixed gear. It is ideal if you want a bike as lightweight and simple as possible, but you fancy having two gears instead of one. On a “normal” bike it would be advisable to stay on mainly flat routes. On an ebike the range of uses is wider, and you can pedal on some easy uphill sectors, though the gear can still feel too hard. Better couple it with a front hub motor, because a central motor could struggle with the low RPMs when going uphill.
- Sram DD3 Pulse: this is a new system, which has been available only for a few months. A hub gear works in a similar way to the Automatix we have just mentioned, changing gears based on the speed of the bike; there are however three available gears, and not only two. Moreover, the DD3 Pulse is coupled to a standard manual derailleur shifting system, for fine tuning the gear. Basically the automatic hub gear takes up the function of the three chainrings to be found in many trekking bikes. It cannot be bought aftermarket to install it on your bike: at the moment it is only available on new ebikes. The Sram DD3 Pulse is compatible with the CANbus standard.
- Shimano Symphomatic: this is also a new product. It is basically the forseeable evolution of the Shimano Alfine hub gear (8 or 11 gears) actuated electronically through the Di2 system, already available since 2014. Adding an ECU which “decides” when to change gears, based on the speed and the cadence, is relatively simple. The system is available on Shimano STEPS ebikes; its integration guarantees for instance that the power of the motor is reduced at the time of shifting, to reduce stress on the transmission
- Continuously variable and automatic gear-shifting sytems Nuvinci N330, N360 and N380. This is probably the most interesting technology for a city ebike. The gear is continuously variable: this is means that there isn’t an X number of predetermind gears; within the hub there are a series of gears which allow for a very fine tuning of the pedalling gear; the cyclist experiences a smooth transition, and never feels a more or less brusque change from one gear to the next. The system can automatically change gears in order to maintain the desired cadence. For instance, you can select a cadence of 70 RPM: the Nuvinci gear will automaticall and continuously change the gear in order for you to stay on that cadence.
The main difference between the three available models is how wide the range of gears is: the number (330, 360 or 380) indicates the difference (in percentage) between the hardest gear and the easiest gear). Basically, if the simplest gear has a metric development of X meters, the hardest gear on the N380 model will have a metric development of 3,8X meters. The Nuvinci automatic gear is available on many Bosch ebikes.
Here is our in-depth test of the NuVinci N380.
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We think it is just a question of time: in the next few years ebikes with automatic gear shifting systems will be more and more widespread in our cities.
What do you think about it? Would you like to have an ebike with automatic gears, or do you prefer to keep the maximum control over the gear you use?