Bike Gears: Understanding the Drivetrain

The drivetrain is the heart of your bike, because the system that allows you to ride! Pedaling and riding sounds simple, but this mundane action results in a succession of components and movements. You need to understand the basics of how it works, know the type of transmission you have, in order to shift gears at the right time, and know how to maintain it.

By pushing on the pedal, the cyclist turns the pedals. This consists of three parts: the pedal serving as a support surface, which is attached to the crank, which connects the rotating front plate in concert with it. A pedal stroke thus induces a movement of the chainring and therefore of the transmission. A double or even a triple plate can exist, especially on the MTB or hybrid bike, while an e-bike usually contains only one. The size of the chainrings depends on the number of teeth.

In order to transmit the movement to the rear wheel, the crankset drives a chain, a long succession of metal meshes. It fits perfectly on the teeth of the front chainring and those of the chainring(s) at the rear called sprockets. When there are several of them, they form a cassette.

The transition from one sprocket to the other is controlled by a rear derailleur, a complex multi-piece component located below the cassette, which is controlled mechanically or electronically.

Don't forget the notion of gearing, which is essential in the lexicon of road cycling or on a MTB. This is the ratio of the number of teeth in the chainring and the smallest sprocket in the cassette (or single sprocket): example 49-11. The number of teeth of a cassette is the number of teeth of the small and large sprocket, such as 10-52.

Good to know, the multi-speed transmission by derailleur is the most common, but it is not the only one. Here are some other types of transmissions you can find:

• Single-speed: a single sprocket (or chainring) with a carbon and plastic composite chain or belt, common on an urban bike;
• Fixie: single-speed but with fixed gear, without freewheel so the rear wheel turns at the same time as the crankset;
• Hub: a block closed to small sprockets without derailleur (examples: Shimano Nexus or Sturmey Archer on the rear wheel, or to the Pinion crankset) or of the manual variator type (Enviolo);
• Automatic gearbox: hub format (Bafang 3-speed or Enviolo Automatiq variator), with the bottom bracket on a multi-speed electric bike such as an Ultima bike with a Valeo Cyclee motor or variator (Decathlon Owuru).

Shifting is the role of the derailleur, shifting the chain to the right sprocket of your electric bike. This derailleur is controlled by a gear selector on the right side of the handlebars. This selector is either a twist handle or a "pusher" gear lever on the handlebars. From the handlebars to the derailleur, the bike needs a cable (sheathed for protection), or an electronic transmission (Shimano Di2 or SRAM AXS for example).

This seems absurd, but the largest sprocket is the one with the lowest gear, and therefore the smallest sprocket is linked to the higher speed. The small gears - or large sprockets - are those to be used on sustained climbs or when starting, with the rider having to gradually increase the gears on the smaller chainrings. This allows you to maintain a regular cadence while gaining speed on the bike. The smallest chainrings - and thus the highest speeds - are therefore to be reserved for high speeds and downhills.

As for the other types of multi-speed drivetrains, the Shimano or Sturmey Archer hub works on the same principle (and when stationary!). The Enviolo hub (formerly NuVinci) is a progressive rotating shifter that changes the resistance of the drivetrain.

The drivetrain differs greatly from one type of bike to another. In the city, there is no need for performance and you generally don't ride a bike very fast (15-20 km/h on average, with peaks of 30 km/h). The urban cyclist can be satisfied with a 6-speed transmission to evolve in this environment, unless he encounters many differences in altitude (Lyon for example). Some people are satisfied with one gear, but a city bike contains a speed range from 1 to 8 depending on the model.

On the contrary, the mountain biker must be able to be comfortable at all times at regular pace, on all terrains such as the Vanoise National Park, whether uphill or downhill. OneMTB Electric vehicles therefore require more gears, between 10 and 12, in order to be more efficient on elevation gains, or even - very rare - several front chainrings to multiply the gears. The same goes for a road bike or a gravel bike that requires a lot of amplitude. A Bianchi E-Arcadex can go up to 13 gears by opting for a Campagnolo drivetrain!

Between the two, VTCs are less demanding, but must maintain between 7 and 10 gears for a comfortable ride on the Loire à Vélo for example. The move upmarket of the references are closely linked to the speed of gear changes. Performance enthusiasts will be very sensitive to SRAM XX Eagle drivetrain names on a Specialized Turbo Levo e-MTB while an urban cyclist will settle for an entry-level Shimano Tourney on his Decathlon Elops 120E city bike!

Fewer speeds lead to fewer chainrings and therefore fewer parts that can cause problems. Already, the risk of derailment decreases with the lower number of gear changes. A cassette with less speed, or a single sprocket, also means less lubrication. Even better, a bike with a typical belt drive Giant DailyTour E+1 LDS requires even less maintenance!

As we said, fewer speeds mean less versatility. You will have more difference between the gears to cover the same range of speed (let's say between 0 and 35 km/h). As a result, you will not find a comfortable cadence in certain situations: you will struggle more when starting, especially at high speed where you will "grind".

Low speeds are to be used at low speed. This means that you will have your natural pedaling frequency when starting off or when you tackle a climb. If the slope flattens or when you accelerate, you have to increase the gears. Finally, by reaching a stabilized speed, there is no need to switch from one sprocket to another. However, you should not hesitate to use a higher or lower gear, to feel as comfortable as possible or to optimize your mid-speed performance on your road bike .

In the case of a Nexus or Enviolo "hub" type bicycle transmission, gears can be shifted when stationary, unlike a derailleur transmission. But be careful, the Nexus don't like to change gears while pedaling! On an Enviolo variator, you have to turn the lever gradually under acceleration to increase the gear (the pedaling hardness), and

If you are looking for optimal performance off-road, for example on the Grande Traversée du Massif Central, it is best to anticipate. This consists of dropping speed before a corner, to get back on track at the right pace on the exit, and find better grip in the process. The same thing happens before attacking a hill, especially if you have a nervous electric bike - such as the Bosch SX - requiring a high pedaling cadence to deliver power.

This is less noticeable on a mechanical bike, where the inertia allows you to maintain a high speed on approach and then gradually descend to low speed to increase your cadence. On flat terrain, the gear change depends mainly on the speed at which you ride.

If you brake to stop, lower your gears to a large sprocket before stopping to restart comfortably. Then gradually shift gears along your acceleration, preferably in tandem with your optimal cadence to improve performance!

You can follow the route the old-fashioned way via PDF or paper. Better still, because we're in the 21st century, you can consult the route on a bike application via a GPX file.

Finally, for your own safety, it's best to be accompanied, either in pairs or in groups. If you like to go it alone, make sure you're geolocated via an app in case of trouble, and that your phone is fully charged with a back-up battery. In fact, some MTB electric bikes include a USB socket or induction charger!

Especially off-road, in autumn or winter for urban cyclists, the chain collects dust, gravel, leaves or mud. All these elements will hinder the proper functioning of the chain and therefore of the transmission, or even wear it out prematurely.

A brush and a little water are enough to clean the chain, remembering to go through all angles on the derailleurs(s). You then have to apply a biodegradable degreaser to remove the "old" grease and then regrease the chain with a few drops, remembering to turn the crankset and change all the gears to grease all the chainrings.

Over time, or after an impact, a derailleur can become out of adjustment. This means that the handlebar control won't result in a precise shift, giving the impression that the chain is reluctant to shift from one gear to another, or even preventing the use of certain sprockets or chainrings!

Here's how to adjust your bike's gears:

• Two small screws on the derailleur change the stops of the larger and smaller chainring
• These stops can move a few millimeters to the right or left, turning a screw a quarter turn can be enough
• The screw on the left corresponds to the stop of the large pinion (speed 1), the one on the right to the stop of the small pinion (maximum speed).
• You have to fumble a little, turning the crankset and changing gears several times to "feel" the right gear change on the handlebar control.

If adjustment is not possible, you have to look at the side of the cable, which can be too tight or little tightened. It is possible to adjust it with the dial at the point of connection to the derailleur: clockwise to add tension (if the gears rise badly) or counterclockwise to remove it (if the gears go down with difficulty).

Less common, play may appear on a derailleur roller, to be changed, or the hanger is damaged, twisted or replaced. These operations are less easy to carry out, you can go to a Shimano Service Center shop or workshop, if your bike is equipped with a derailleur transmission (Shimano Tourney, Alivio, Cues, Deore, etc.) or if you have a problem with a Nexus or Alfine hub.

Fewer gears can relieve driving, as it jerks less acceleration, especially if you are looking for riding comfort on a bike or already stressful daily commutes. Some bikes are even single-speed, allowing you to ride with a free mind, but with more effort to make and less versatile.

Reducing the number of gears is also synonymous with less maintenance of the electric bike : less wear, risk of derailleur deadjustment, lubrication and breakage.

If you already have a bike and don't know how many gears, or are eyeing your next purchase, it's very simple. The number of sprockets defines the number of gears in the case of a derailleur transmission, with a front single chainring. If you see several front chainrings on the bottom bracket, you have to multiply. Here are some gear combinations: 2x11 = 22 speeds, 3x8 = 24 speeds, etc. Conversely, a single sprocket at the rear is synonymous with a single-speed bike.

Simpler or to confirm your calculation, handlebar controls very often have numbers. This method is the only way to check the number of gears in a Nexus or Sturmey Archer hub drivetrain. More rarely, the number of gears of an automatic gearbox (Valeo Cyclee, Bafang) is checked on the screen of the electric bike, by pressing the "+" button.

On a city bike, cleaning should be done at least every month, or even more regularly in the autumn or winter due to the weather conditions. If you are a fan of hiking or outings MTB and gravel, maintenance is optimal after every long journey.

Before buying your electric bike, it is therefore recommended to aim for the number of gears corresponding to your practice. Don't forget about maintenance, which is cleaning - especially in autumn, winter and off-road - and regularly greasing your chain.

Also know how to change gears at the right time to avoid grinding or struggling too much, especially if you are aiming for performance. We hope that these tips will allow you to ride in the most efficient way on your e-bike or e-MTB!