Choosing a Road Cycling Cassette

Also known as a sprocket or rear block by newer riders, choosing a road cycling cassette is probably one of the most underrated ways to improve your riding, especially on the hills.

So, what are the most important factors here? We’ll look at the following factors:

  • Range of cassette
  • Size of biggest/smallest cogs
  • Cassette weight

Range of cassette

A cassette will either be described by cyclists as wide or narrow. A wide cassette has a large range, meaning the differences between your biggest and smallest gears will be large. This allows you to ride fast on the flats and still ride at a sensible cadence on the hills. Meanwhile a narrow cassette will make it much harder to ride up hills, as the rings tend to have fewer teeth.

If a cyclist is looking for one cassette to use in all situations I recommend a cassette with a wide range. You never know when you might find yourself at the bottom of a leg sapping climb on tired legs with no gears left. A narrow cassette is generally only used for specific events like flat triathlons or time trials. The small gaps between gears helps you find your “Goldilocks” gear while wide cassettes can make it hard to get comfortable if you’re forever in a gear slightly too hard or too slightly too easy.

As an example, an 12 speed 11-23 has rings with the following number of teeth: 11/12/13/14/15/16/17/18/19/21/23. In comparison a 32-11 has 11/12/13/14/16/18/20/22/25/28/32. If I was riding on my 11-32 at a power which suited a 15 tooth cog gear on the back, I’d have to choose between a 14 tooth or a 16 tooth, where if I was riding an 11-23 I could ride in the 15 tooth cog I was after. If you’re riding on rolling terrain this isn’t such an issue as you’ll never be in the same gear for long enough for it to be noticeable. But if you’re taking on a flat course such as Ironman Barcelona, you don’t want to spend 180KM unable to find a comfortable gear.

Range is intrinsic to the size of your biggest ring, which we’ll look at next.

Size of biggest/smallest rings

Cassettes are expressed numerically, such as 12-28 or 11-32. The first number refers to the smallest ring, the larger number to the biggest ring.

If choosing a road cycling cassette for a series of punishing climbs you’ll want to take a 28 at the very least. Potentially even a 30 or 32 if it’s an especially hilly ride.

23 is the lowest number of teeth you’re likely to find on the biggest ring of most cassettes. This is only recommended for strong cyclists riding on flat courses. 25 is traditionally what a lot of professional riders will use, dropping to 28s on mountain stages. For us mortals however 28 is a sensible all round cassette as we don’t have the power to push round a 25 tooth cog on a steep grade without wobbling all over the road.

The smallest rings are generally 11 or 12t (the t denoting number of teeth). These won’t make an enormous difference to your riding unless you’re planning to ride hard on the downhills.

Weight of cassette

Some cassettes cost £50 and some cost well over £300 (Campagnolo we’re looking at you). So what’s the difference? Assuming it’s the same brand and has the same number of gears/teeth, it’s just the weight. You can buy an expensive cassette to shave off a few grams, but that really is it. Shimano’s cheapest 11 speed 11-28 cassette, the 105, weighs in at 284g, with their top of the range Dura-Ace equivalent topping the scales at 192g. The 105 cassette retails at £50, the Dura-Ace at £199, so this is a very expensive way to save <100g. There may be minute differences in shifting performance, but you’re unlikely to notice them if your gears are indexed properly.

Weight data courtesy of https://ccache.cc/blogs/newsroom/2019-road-groupset-weight-comparison

Conclusion

If I were to advise a new road cyclist, I’d recommend an 11-28 at the very least to help them up the hills. As they get stronger or if they live somewhere with very few hills they might consider a 25. I would only recommend a 23 for competition day, or race simulation rides, as the ability to get up a hill efficiently far outweighs the benefit of the smaller jumps in gears for me.

Most road cyclists will acquire a collection of cassettes over the years. This gives them the flexibility to choose the right cassette for different rides. I wouldn’t necessarily swap between a 30 for my hilly training rides and my 25 on flat training rides, but if I had a big ride (100 miles plus) or a race, I’d take the time to choose the right tool for the job.

Technical info

Hopefully we’ve enlightened you to the benefits of choosing a road cycling cassette. But before you go and place your order, some really boring stuff. It’s easy to buy a cassette incompatible with your bike, so make sure you avoid the following pitfalls

Manufacturers are generally not cross compatible. Some Shimano and SRAM products will work with each other, but check with your bike shop before buying. Campagnolo is not compatible with any other manufacturer.

Make extra sure you’re buying a cassette which has the right number of gears. As both 11 and 10 speed cassettes are still expressed as 12-28, this is an easy trap to fall into. To complicate matters, older versions of group sets have less gears, so make extra certain it’s the product you’re after before ordering. Each generation of a groupset will have a code (such as Shimano R7000), so make sure you’re getting the right kit. It’s worth checking with your bike shop if you’re unsure what you have on your bike. As long as you order it through them, they’ll be happy to help.

The cassette that was on your bike when you bought it is often the largest it can take. If you want to go above this you’ll need to upgrade to a long cage rear mech. This isn’t an expensive upgrade, but it’s best to order and install the parts together to save on labour costs if you’re unsure how to do it yourself.

Finally, your cassette is a consumable part and will wear over time. The best way to prevent this is to keep your drivetrain clean. Find out how in our article here

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