# What Gear Is a Fixed Gear Bike In? Gear Ratios Explained

It might sound like a silly question, but if a fixed gear (or single speed) bike has only one gear, then which gear is it exactly?

You may be used to multi-speed bikes that have between 7 and 11 sprockets across from 2 or 3 chain rings that can be combined to produce whatever gear ratio is most appropriate for any given scenario.

When you strip away all those extra cogs and components, which combination of sprocket and chain ring are you left with? Which one is the best? And can it be easily changed?

**Fixed gear bikes are commonly sold with a 46 tooth chainring and 16
tooth sprocket giving a gear ratio of 46:16. Fast enough on the
flats, but not too hard on the hills. It’s equivalent to 52:18, which
might be the larger chainring and 4th position sprocket on a
multi-speed bike.**

This is a simplified explanation and the exact details vary depending on the gearing configuration of the multi-speed bike in question. But before we go into details, we need to be sure what exactly a gear ratio is, and how we conventionally talk about them.

## What is gear ratio?

Put simply, a bike’s gear ratio is a number that tells you how ‘easy’ or ‘hard’ its gearing setup is.

The higher the gear ratio, the harder you must push the pedals to maintain the same speed. Lower ratios are more ‘spinney,’ meaning a higher cadence for the same speed.

Technically, gear ratio is a dimensionless measure of the *mechanical
advantage* of the drivetrain. It’s a way to express how many
rotations the rear wheel will make for each full turn of the cranks.

The way a gear ratio is calculated is by taking the fraction of two whole numbers: the number of teeth on the chainring (the front cog) divided by the number of teeth on the sprocket (the rear cog).

They’re typically represented using colon notation; for example, 46:16 is the gear ratio of a bike equipped with a 46 tooth chainring and 16 tooth sprocket.

### Decimal representation

Sometimes you’ll see a gear ratio written as a decimal, like 46:16 can be written as 2.875. If you punch 46 divided by 16 into your calculator, you’ll get 2.875. But 2.875 what? I told you it’s a dimensionless quantity, so what exactly is it supposed to convey?

What this means is that, with this 46:16 gear ratio, the rear wheel makes almost three (2.875) full turns with each revolution of the cranks.

There are more sophisticated ways to measure the mechanical advantage
of a bicycle, most notably *gear inches* which takes into account the
diameter of the rear wheel (including the tire’s width). But since
almost all adult bicycles these days have the same 700c rim diameter,
and tire width is a somewhat negligible addition, we can ignore that
factor and talk about gear ratios in terms of teeth count alone.

Now that we know how to talk about gear ratios, let’s dive into an example.

## Comparison with a typical road bike

This is where we have to use a bit of math. But don’t worry, I’m going to explain everything using everyday language.

Let’s say we have a multi-speed road bike equipped with two chain rings of 42 teeth and 52 teeth, and a cassette of sprockets ranging from 11–28 teeth.

The sprocket in the fourth position of this cassette typically has 18 teeth. So, if you were riding this bike “in fourth gear” and with the chain over the big ring, you’d be riding with a gear ratio of 52:18 which, dividing 52 by 18, rounds to 2.88.

This is a very close approximation of our most common fixed gear ratio, which is 46:16. Written as a decimal, that’s 2.875.

So, to get an idea of what it’s like to ride a 46:16 single speed bike, you could simply shift your road bike onto the larger chainring and fourth sprocket. That is, if your gearing setup matches our example above.

But what if your gearing setup is different? In the next section, we’ll learn how to find out what gear on your multi-speed bike best matches the gear ratio of any single speed bike you might consider buying.

## Finding equivalent gear ratios

How did I arrive at the 52:18 combination? I could have taken a brute force approach, trying out each possible combination of chain ring and sprocket teeth counts. However, there’s an easier way.

Now we’re really getting deep into the weeds of gear ratio calculations. This is where a lot of people switch off (and I don’t blame them!). So if you’re still with us, well done.

Fortunely, finding equivalent gear ratios is very easy with a simple chart shown below. This way you don’t even need to do any calculations.

The numbers along the top represent the number of teeth on the chain ring, while the numbers down the leftmost column represent the number of teeth on the sprocket. Dividing the former by the latter gives you the decimal value in the table.

Teeth | 40 | 42 | 44 | 46 | 48 | 50 | 52 | 54 |
---|---|---|---|---|---|---|---|---|

11 |
3.6 | 3.8 | 4.0 | 4.2 | 4.4 | 4.5 | 4.7 | 4.9 |

12 |
3.3 | 3.5 | 3.7 | 3.8 | 4.0 | 4.2 | 4.3 | 4.5 |

13 |
3.1 | 3.2 | 3.4 | 3.5 | 3.7 | 3.8 | 4.0 | 4.2 |

14 |
2.9 | 3.0 | 3.1 | 3.3 | 3.4 | 3.6 | 3.7 | 3.9 |

16 |
2.5 | 2.6 | 2.8 | 2.9 | 3.0 | 3.1 | 3.3 | 3.4 |

18 |
2.2 | 2.3 | 2.4 | 2.6 | 2.7 | 2.8 | 2.9 | 3.0 |

21 |
1.9 | 2.0 | 2.1 | 2.2 | 2.3 | 2.4 | 2.5 | 2.6 |

25 |
1.6 | 1.7 | 1.8 | 1.8 | 1.9 | 2.0 | 2.1 | 2.2 |

28 |
1.4 | 1.5 | 1.6 | 1.6 | 1.7 | 1.8 | 1.9 | 1.9 |

Table: Gear ratio (1 d.p.) according to sprocket and chain ring teeth count.

In our example from the previous section, we showed that 52:18 was equivalent to 46:16. You can read the values from the table above to verify this yourself. Note that the values have been rounded to 1 decimal place, so 46/16 = 2.875 becomes 2.9 for example.

Let’s say you’re looking to buy a fixie that comes with a 46:18 gear ratio (meaning a 46 tooth chain and 18 tooth sprocket). What gear could you try on your multi-speed bike that would be roughly equivalent?

Well, if you look up 46:18 on the chart, you’ll find 2.6. So anywhere else on the chart where it says 2.6, you know it’s an equivalent gear ratio.

For example, 54:21 has the value 2.6 meaning you could try combining
your 54 tooth chain ring with your 21 tooth sprocket. Values like 2.5
and 2.7 are *close*, so something like 52:21 or 40:16 would be
*roughly* equivalent.

## Changing the gear ratio

Let’s say you bought a fixed gear bike that came with the standard 46:16 gear ratio. You like riding it, but you just wish the gear was a little easier—that way, hill climbing wouldn’t be such a pain.

Well, what you would probably do is swap out the 16 tooth sprocket for an 18 tooth sprocket. This would decrease the gear ratio from 2.9 to 2.6. Look up these values in the table to verify this.

In fact, this is exactly what I did because it’s ridiculously hilly where I live.

Another way to decrease the gear ratio would be to swap out the 46 tooth chain ring for a 44 tooth one. This would have a less dramatic effect, bringing the ratio down to 2.8. However, chain rings are usually more expensive and require more work to install compared to sprockets.

Of course, if the opposite is true and you want a *harder* gear
ratio—maybe because your local area is quite flat—then you’d
either switch to a smaller sprocket, or a larger chain ring.