PAP Wonders... Cassettes, Sprockets and Cogs

Our next topic in PAP Wonders... is about cassettes. Cassettes are the gears that engage the chain and the rear wheel. For a brief introduction on cassettes, look at our Parts of a Bicycle article on the drivetrain. We will be talking about the pros and cons of different cassette choices like having more cogs in your cassette and having larger cogs. We hope this can help you on your cassette choice.

My personal choice: a 10 speed cassette with 12-27 range.

Speeds. The definition of "speeds" is the number of cogs (gears) that a cassette (the set) has. For example, 8 speed means there are 8 cogs on the cassette. 9 speed means 9 cogs. 10 speed means 10 cogs. Cassettes can vary from as few as 3 speed to as many as 12 speed. The most common number of speeds ranges from 8 to 11 speed. What is the advantage of having more "speeds"? There are two benefits: Range and Gaps.

Range. The primary benefit of having more speeds or more cogs on the cassette is allowing for a bigger range. Range refers to the difference in size between the smallest cog and the largest cog. The bigger the largest cog, the bigger the range. The bigger the range, the more adaptable the gearing is. A wide range allows one to manage flats, climbs and descents. Mountain bikes have the largest cassettes. The largest possible for 8 speed is 32 teeth. For 9 speed is 34 teeth. For 10 speed is 36 teeth and with modification, the largest can be 40 or 42 teeth. The largest for 11 speed is usually 40 or 42 teeth and the largest for 12 speed is 50 teeth.

 Listed are the different speeds and the widest possible ranges for them.

Gaps. The second benefit of having more speeds is having better "jumps" between each cog. The "jumps" or gaps is the difference in the number of teeth from one cog to the next. For mountain bikes, the large gaps help riders adjust to sudden climbs or descents that are present on the trail. For road bikes, the trend is to have small gaps between cogs. These "tight" gaps help road riders maintain their speed and easily accelerate without feeling a great difference when shifting or affecting cadence too much.

Given the same range, having more speeds means having smaller jumps in between the different cogs.

Wide Range vs Tight Gaps. For mountain bikes. the obvious choice is wide range because the terrain is very much varied. However, the choice for road bikes needs more consideration. For the smaller cogs, the gaps need to be only one teeth and for the large cogs, the gaps can be two or three teeth. Some cassettes, like those shown above, have four teeth gaps between the largest cog and the next. Still, it all comes down to each rider needs and wants. If a rider needs the range, then they can opt to give up tight gaps. If a rider wants to have smoother transitions when accelerating, then he can choose to have tight gaps while giving up range. 

Comparing the common option (for road bikes) 11-28, my personal choice (for racing) 12-27, and my training cassette 12-25. Highlighted are the differences between the gaps of the different cassettes.

I chose to give up the 11 tooth cog because I do not need it as much. Moreover, this range maximizes the number of one teeth jumps. There are only two 2-teeth gaps and two 3-teeth gaps. The largest cog (27 teeth) is only one tooth less than the 28 teeth cog - the size road riders normally use as a climbing gear, This gear gives me the balance I need for tight gears and enough range. [2017 update: I got the chance to purchase a Roadlink and I can now use a 12-30 cassette for courses with a lot of climbing. The 12-30 cassette is similar to my 12-27, except that it sacrifices the 16t for the 30t cog.]

Your Choice. Remember that there will always be a trade off between wide range and tight gaps. If you want tight gaps, then you have to settle for narrow range. This set-up is for criteriums and time trials - both of which are road racing events. If you want wide range, then you have to settle for larger gaps. This set-up is for trail rides and routes with lots of climbs. However, increasing the cassette size might mean you have to purchase a rear derailleur with a long cage (for road bike groupsets) and changing to a longer chain.  Another option will be changing to more speeds but that means changing your entire drivetrain. This allows you to (1) increase the range while relatively maintaining the gaps, or (2) maintaining the range and making the gaps tighter. It is undoubtedly the most expensive option.

When choosing your cassettes, keep these in mind:
1. What you are using the bike for - trails? climbs? flats?
2. Your strengths and weaknesses - strong at flats, weak at climbs?

This concludes our discussion on bike cassettes. I hope you picked up tips on choosing the right cassette for you. It also takes some trial and error. Sometimes, what works for most people does not work for you. Find the right cassette and enjoy your ride.

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