All About Bicycle Gears

Bicycle gears have evolved since the days of 10-speed bikes of the 1970’s. With the advent of mountain bikes in the 1980’s these bikes had a need for a wide gear range to deal with steep uphill off-road terrain. Bikes went from 15 gears, to 18, 24, 27, and then 30. It’s now going back the other way. All high-end mountain bikes are now equipped with 12 gears, and more and more bikes in the mid-range price spectrum are coming with 10 or 11 gears. Does this mean that these new mountain bikes with 10 gears are the same as the 10-speeds from the 70’s? No, actually it’s quite the opposite. Here we will summarise some of the key points of bicycle gearing and why bikes with less gears are easier to use, and more versatile than they’ve ever been before.

Firstly, What’s a Drivetrain?

The gearing system (or “drivetrain”) of a bicycle consists of gear shifters at the handlebar, a cassette (this is the sprockets on the back wheel), a rear derailleur (that’s the part that moves the chain to the various sprockets on the back wheel), a crankset with 1,2, or 3 chainrings (this is the part that the pedals attach to), possibly a front derailleur (this moves the chain across the chainrings), and finally the chain. The number of gears or “speeds” a bike has is determined by the amount of chainrings at the front multiplied by the number of sprockets at the rear wheel. Three on the front and nine on back gives 27 gears for example.

All-About-Gears

What is 1 x ?

(Pronounced “One by”)

All-About-Gears

1 x drivetrains are the modern evolution of bicycle gearing. Manufacturers have figured out how to have the same or very similar range of low to high gears with less moving parts. A 1 x gear system will only have one front chainring. Therefore, there is no gear shifter on the left side of the handlebar and there’s no front derailleur either. There are many significant benefits to this but lets focus on how this relates to the range of high to low gears, as well as the ease of use of a 1 x system. 1 x drivetrains have become so popular that now virtually all mid to high-end mountain bikes are equipped this way. A bike with 12 rear sprockets is referred to as “One by twelve”, or if it has 10 rear sprockets it’s a “one by ten”.

Gear Ratios

A gear ratio is how far the bike will move with one turn of the pedals. If someone is in a low gear that means for one turn of the pedals their bike may only move forward 1.6 metres. That’s ideal going for going up a steep hill. A high gear may move the bike forward 8.0 metres with one turn of the pedals. That’s perfect for riding in a tail wind or going downhill. A gear ratio is not determined by the size of the chainrings or sprockets, it’s actually determined by ratio of them. So just looking at the sprockets and chainrings of a bike and seeing that it might have 27 gears is not the main factor on how suitable a bike may be for a particular purpose or type of terrain.

The calculation of a gear ratio is worked out by dividing the number of teeth on a front chainring, by the number of teeth on a rear sprocket, and then multiplying this by the circumference of the tyre.

Here’s an example of a fairly standard low gear on a 27 speed bike…

  • Front chainring has 24 teeth

  • Rear Sprocket has 34 teeth

  • Wheel size is 29” x 2.1” (approx. 2285mm)

  • 24 divided by 34

  • Multiplied by 2285

  • Equals 1613mm, or 1.613 metres

That means for one turn of the pedals, the bike will move forward 1.6 metres.

Now here’s an example of a low gear from a modern One by mountain bike that might only have 10 or 11 gears…

  • Front chainring is 32 teeth

  • Rear sprocket 46 teeth

  • Wheel size is the same 29” x 2.1”

  • 32 divided by 46

  • multiplied by 2285

  • Equals 1590mm, or 1.59 metres

    Let’s just round that to 1.6 for simplicity sake.

That means for one turn of the pedals, the bike will move forward 1.6 metres.

That’s the SAME LOW GEAR RATIO as the bike with 27 gears, even though the chainring and sprockets are both different sizes.

Sequential Shifting

This is what cars have. From 1st gear to 2nd gear to 3rd gear. Nice and simple, it works well.

Bicycles with multiple derailleurs do not have this, UNLESS they are a 1 x system! Your car doesn’t have two gear sticks, it’s got one right? A bike with 1 x gearing has one gear shifter on the right side of the handlebar only. From the lowest gear, 2nd gear is higher, 3rd gear is higher, etc. This gets back to the ease of use of 1 x gearing.

There’s no need to figure out “should I be in number 2 on the left and number 5 on the right”, or “number 1 on the left and number 7 on the right.” Each gear is in a sequence as you go through the gear ratios.”

How many gears do I need then?

Things have changed from the days of 18, 24, 27, or 30 gears. A 1 x drivetrain is not about how many gears but rather the RATIOS. A bike with 1 x gearing will almost always have a low gear as low or often even lower than a traditional mountain bike. Manufacturers know that riding uphill can be tough and they’re not about tricking people in to making it harder! But what a 1 x system on a mountain bike is optimized for is the speeds that a rider is likely to be doing on off-road terrain or on flat sealed road. This speed range for 99% of people is going to be between 5kmh and 30kmh. 1 x systems often forgo the very highest gear and they do this because the high gear (the “hardest gear”) is always the least used.

Cycling the Alps to Ocean or West Coast Wilderness Trails

We know from our own experience riding the different cycle trails that a 1 x gear system is perfect for the A2O and West Coast Wilderness Cycle Trails, as well as virtually any other cycle trail in New Zealand or around the world. The range of low to high gears is suitable for a variety of fitness levels on terrain from uphills on off-road sections to flat sealed road portions. These modern bikes are easier to use and run smoother than outdated 24 or 27 speed systems. This takes focus away from operating the bike and allows the rider to relax more and enjoy the amazing scenery of the environment that they are cycling in.