How to Choose the Best Cassette for Triathlon? What You Should Know!


Your bike’s gearing system can make a big difference in how easy or hard it is to ride, not to mention how many gears you’ll be able to utilize. Any bike you buy will come with a certain amount of gears (unless it’s a single-speed, of course).

But more gears doesn’t always translate to “better.” Having more gears means having more components which can lead to added weight for the bike.

So how do you choose which is best for you? And what even is a cassette, anyway? We’re going to answer those questions and more.


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What Size Chainring Do I Need for A Triathlon?

Generally, a 52/36t is your best bet as the size sits right between a compact crankset and a standard crankset , but you may want to opt for 50/34t if you’re a beginner. Before we explore finding the right size. (Source)

let’s dive into what the numbers actually mean.

Chainrings/Crankset

Let’s start with the front. The gears at the front, attached to the bike’s pedals, are referred to as chainrings or a crankset. Most road or triathlon bikes will have two or three chainrings up front.

If a bike has two chainrings, it may be referred to as a double or a two-by (abbreviated to 2x). The same goes for three chainrings (triple, three-by, 3x). Mountain bikes will typically only have one chainring (a “one-by”). The smallest chainring will be closest to the bike, with the largest on the outside (Source).

Generally speaking, the smaller the chainring, the easier the pedaling. 

Cassette

The back gears are collectively called a cassette and the individual rings themselves are called cogs. They are grouped in ascending order with the biggest cog closest to the wheel and the smallest on the outside.

The larger the cog, the easier it is to pedal and the slower you’ll go so it’s usually used for climbing. Rear cassettes will be written as two numbers with a dash between them, starting with the size of the smallest cog and ending with the size of the biggest cog. For example, 11-23 (or 11-23t).

The number refers to how many teeth the cog has.

Teeth

The chainrings and cogs will both have numbers associated with them. These numbers refer to the number of teeth on the gear (which is why sometimes you’ll see a “t” for teeth at the end).

For a crankset, the first, bigger number is the larger gear and the second number is the smaller gear.

Do TT Bikes Have Gears?

Yes, time trial bikes will have gears. Some riders will opt to use the standard 11-28t cassettes that are often found on road bikes, while others will opt for 11-23t which reduces the size of the steps between each cog, allowing for more gradual and precise shifting.

In fact, some triathletes who use TT bikes will choose to use a one-by crankset to remove any potential drag that a front derailleur may cause and ultimately lighten the weight of the bike. This can be especially useful in courses where the little ring wouldn’t be used much anyway.

How Many Gears Should a Triathlon Bike Have?

Most riders will want a 10 or 11-speed gearing system. This would mean either a cassette that has 10 or 11 cogs in the back. Some bikes are referred to as “18 speed” because they have two chainrings in the front and a 9-speed cassette (9×2=18). However, that isn’t strictly correct so most bikers will refer directly to the number of cogs they have (i.e. “10 speed”).

It can also help to understand the gear ratio of your bike. This ratio reflects the difference between the number of teeth between the front chainring and the chosen cog in the back. The hardest gear would be on the biggest chainring and the smallest cog (therefore, the biggest ratio). Let’s use a 50/34t by 11-32 bike as an example:

52 (biggest front) ➗ 11 (smallest back) = 4.73 gear ratio

This means that every full rotation of the pedals moves the back wheel 4.73 times.

This also explains why it’s easier to climb in a lower gear: you can increase your cadence to spin the wheel more, rather than needing to put out more direct force.

You can put all of these numbers in a table to make it even easier to understand and see the full range of your gears. Here’s a table using our 52/36t by 11-32t setup, but you can do this for any pairing.

# of Teeth (Small Back Cog)52 Teeth (Front chainring)36 Teeth (Front chainring)
114.733.27
124.333
1342.77
143.712.57
163.252.25
182.892
202.61.8
222.361.64
252.081.44
281.861.29
321.631.13
Bike Gear Ratio Calculation Table

How Do I Choose a Chainring and Cassette?

First, figure out what your current setup is, especially if you purchased a bike without thinking much about your gearing. Play around until you find the gear that you find yourself riding in most often – any gear set that you get going forward should include that.

Choosing a 52/36t chainring is an excellent option for most triathletes because it can provide the best of both worlds: a large, 52 tooth gear for speed through the flat portions and a 36 tooth gear for climbing. A 52/36t is often called a “semi-compact” chainring.

A 50/34t may be a good option for athletes who aren’t as strong or who are constantly having to ride hills. This would be referred to as a “compact” chainring. A standard chainring is 53/39t. You can combine any of these with any number of cassettes to get a wide range of bike gear options.

Once you’ve figured out your front gearing, you can move on to the cassette. If you run an 11-speed cassette, then you’ll likely want a cassette that’s 11-25t or 11-28t. That way you can maintain your cadence more easily when shifting between gears. If you pair a 11-28t with a 52/34t crank, you’ll have the option to ride at 34 in the front and 28 in the back which is small enough for super steep climbs. You’d also get to shift up to 52 by 11 on the downhill or when the wind is at your back.

How Long Does a Bike Cassette Last?

A bike cassette can last anywhere from 4,000 to 6,000 miles and sometimes even longer. It will last longer the more maintenance you put into your bike, especially if you change your chain regularly (Source).

You’ll also want to make sure you’re taking care of your derailleur as that can increase the life of your cassette. You may even have the option to replace individual cogs, so you can swap out the ones you ride in most often without having to get a brand new cassette.

For more on this topic, check out our post How Many Miles Should a Bike Chain Last? What to Do About It ?!

Final Thoughts

There’s no perfect answer when it comes to choosing the best crankset and cassette for a triathlon. Ultimately, it’s up to you to decide how you want to ride and what works best for your skill and ability. Keep trying different options until you can dial in your ideal fit.

Aprill Emig

Based out of Duluth, MN Aprill loves to write about the outdoors, education, and all forms of adventure. You can find her mountain biking, running, or playing roller derby.

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