Nearly all bicycles require the rider to shift gears manually, although many bikes have only a single speed and do not shift at all.
Shifting gears on a bicycle is easy, but continually thinking about whether you’re in the right gear can take some of the fun out of a ride.
You might think there’s got to be an easier way…and there is, but only kind of.
Here’s whether bicycles are automatic
Automatic shifting bikes exist but are very rare. They typically use a centrifugal clutch mechanism to shift based on wheel speed and/or pedaling cadence. More recently, some electronic derailleurs have added partially automated shifting. In that system, the rider manually shifts either the front or rear, and the computer automatically shifts the other derailleur automatically. However, this remains expensive and fairly uncommon.
Background: how (most) bicycles shift gears
Derailleurs are the most common
Most manual and automatic bicycles both shift gears with a spring-loaded pulley called a derailleur, as pictured above.
The derailleur connects via a cable to a shifter, which is usually located on the handlebars. When the rider adjusts the shifter, it tightens or loosens the cable. This moves the pulley in or out to align the chain with a different gear. When the moving chain catches on the new gear’s teeth, the shift is complete. It happens in about one second, depending on the derailleur model, maintenance, and number of gears shifted across.
Front derailleurs work similarly, but are a little simpler. Instead of a pulley with springs, most have just a simple metal guide. That’s because they only need to reach 2-3 gears, not the 7-12 that a rear derailleur uses.
Internally-geared hubs are a popular alternative
The other style of shifting is through something called an internally geared hub.
This system, known as an IGH for short, replaces the external gears and derailleur with a system of tiny planetary gears all sealed inside the rear hub.
An IGH is heavier and usually more expensive than derailleur gears, but requires far less maintenance and is basically impervious to weather.
Although the engineering and design are completely different, the rider’s experience is very similar. (However, most IGHs shift best while not pedaling whereas derailleurs require pedaling.)
Both derailleur and internal gears put the rider completely in control of the gear.
If pedaling feels too easy, you can quickly shift to a harder gear. If pedaling feels too hard, you can quickly shift to an easier gear.
With just a tiny bit of practice, it becomes easy to manually maintain a steady and comfortable rate of pedaling by switching gears based on the terrain and your energy levels.
Do any bicycles have an automatic transmission?
Over the years, a few manufacturers have offered automatic shifting bicycles.
Most use a standard derailleur, with an added centrifugal spinning mechanism that expands/contracts and triggers a gear shift as the wheel speed increases or decreases. There are also a few internally geared hubs that work on a similar principle, but are usually limited to just two speeds.
Here’s an example from the old LandRider Auto Shift, which was one of the only automatic bicycles ever sold at a (somewhat) large scale:
One current option: Shimano Di2 Synchro Shift
As of writing, the closest example to auto-shifting is Shimano’s Synchro Shift option for its Di2 electronic derailleurs.
It does one of two things:
- Shift the front derailleur automatically when the rider shifts past a predefined gear in the back
- Shift the rear derailleur automatically when the right shifts in the front
This helps prevent cross-chaining, which is when the chain is pulled sideways because of using the left-most front gear with the right-most rear gears or vice-versa.
Synchro Shift is partially automatic in the sense that the rider still controls most of the gear range, and the system responds with an additional shift to keep the front-rear gear combination optimal.
Here’s their promotional video for a closer look.
Is automatic bicycle shifting worth it?
Since automatic cars are so popular, you might wonder why automatic bicycles are not.
The answer is that automatic shifting, by definition gives you absolutely no control and therefore no ability to push a harder gear or relax in an easier gear than whatever the mechanism chooses.
For instance, if you want to work a little extra hard while standing up to climb a steep hill, you would manually keep your bike in a higher gear but the auto shifting bike would force you into a lower gear. It’s sometimes possible to adjust the shifting threshold, but that’s still nowhere near the same as controlling each individual shift.
For that reason, automatic bicycle transmissions have never sold particularly well. (Shimano Synchro Shift is somewhat of an exception, but it’s more like automatic adjustment to manual shifting, not purely automatic shifting.)
You could also argue that it’s a complex solution to a problem that doesn’t exist.
Shifting gears with a well maintained derailleur or internally geared hub is simply not difficult. Even if new riders find it a little much to think about, it rarely takes more than a few minutes to feel comfortable and a few hours to feel like second nature.
Additionally, even automatic bicycle drivetrains still need to be adjusted and tuned. They just add more mechanical complexity on top of the springs and cables that you’ve already got to tend to.
If your goal is to avoid having to think about shifting, then consider a single-speed bike instead. The obvious disadvantage is having only one gear, but it is the classic, low-tech, low-maintenance alternative to fretting about derailleurs.