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You might need a smaller chainring

By Bruce Lin

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Choosing the best 1x chainring size for mountain bikes and gravel bikesSize matters, at least it does with 1x drivetrains. Picking the right chainring is important because it gives you the gear range to handle your local terrain. But how do you figure out what size you need? Gear up with this easy guide. 

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Standard chainring sizes

1x chainrings come in 2 tooth increments and many 1x mountain bikes and gravel bikes come from the factory with a “standard” size chainring, usually 32t for mountain and 42t for gravel. These sizes became standard because they mirror the size of the middle (and most used) chainring in older 3x drivetrains. Cassettes, rear derailleurs, and bikes have been designed to accommodate this mid-sized chainring. For many riders, this will be fine for everything from recreational riding to racing.

Why you should try a smaller chainring

Rebecca Rusch Private Idaho 42t 1x gravel chainringThe Queen of Pain, Rebecca Rusch, said she sized down her chainring to conquer the tough climbs at her namesake race. Photo by: Wyatt Caldwell / Redbull Content Pool

If you need easier gearing, just swap to a smaller chainring. This is good for riders who struggle with climbing, regularly ride steep terrain, or carry extra weight with bike bags. On a mountain bike, the small change of swapping from a 32t to a 30t chainring gives you gearing that is 6.7% easier. For gravel, going from a 42t to a 40t provides 5% easier gearing. That could be the difference between conquering a steep climb and being forced to get off and walk. We like riding bikes, and successfully cleaning a climb is always more fun than hiking. 

Mountain bike chainrings are available in smaller sizes all the way down to 26t, though I’d recommend most riders try a 30t or 28t first to experience how much easier it is to climb. For gravel bikes, I wouldn’t recommend going any smaller than 38t to maintain top-end speed on downhills. As a general rule, you can change the size of your chainring 2 teeth without changing your chain length. If you go more than 2 teeth smaller, you will need to shorten your chain. 

With smaller chainrings, you may find yourself spinning out on fast downhills. Personally, spinning out is always preferable to being overgeared on climbs. Easier climbing gears keep my legs fresh and allow me to tackle ambitious rides. For regular riders, saving energy and preserving your knees through spinning, and completing tougher routes will enhance the overall experience of riding. 

Extra nerdy tip: On my full-suspension mountain bikes, I like how the smaller chainring increases anti-squat, which firms up the rear end for efficient climbing. 

When to go to a bigger chainring

Nino Schurter and Mathieu van der Poel world cup XC mountain bike 38t chainringsPros like Nino Schurter (left) and Mathieu van der Poel can mash big chainrings up climbs. We probably shouldn't copy them though. Photo by: Bartek Wolinski / Red Bull Content Pool

Bigger chainrings are great for riders who need more top-end speed or ride mostly flat terrain. When using my 29er hardtail as a gravel bike, I swapped to a 36t chainring to keep up with drop-bar gravel bikes on flat roads. Look at pro racers and you’ll see many using bigger chainrings. 

There are two main reasons racers upsize rings. First, they are fitter and faster than the general population. They need to sustain higher speeds and have no problem climbing with harder gears. 

The second reason is more nuanced; 1x drivetrains are simple and reliable, but one drawback is increased chain angle at the extremes of the cassette. When the chain isn’t straight, there’s more friction, which leads to a slight efficiency loss. Choosing a chainring that allows you to stay in the center of the cassette maximizes drivetrain efficiency. Bigger chainrings also reduce friction because the chain doesn’t articulate as much when wrapping around it. 

My advice: Unless you’re a pro or in the top 10% of riders, those small efficiency increases probably don’t matter. You’re better off prioritizing climbing gears and using the smallest chainring possible.  

Choosing a chainring with a gear calculator

Gear calculators are a great tool if you want to compare chainring options. To calculate the difference in gearing between 32t, 30t, 42t, and 40t chainrings, I used Sheldon Brown’s classic gear calculator. Seeing the difference as a percentage convinced me to try racing with a 30t chainring on my quiver-killer mountain bike

Another favorite of mine is this HTML gear calculator. It provides a visual comparison of different drivetrains. 

1x gravel bike drivetrain gear rangeIn the above example, I compare a 1x drivetrain with a 42t chainring and 10-42t cassette to a compact road drivetrain. For gravel, I know a 42t chainring will work because it has a similar range to the compact while providing an easier low gear for climbing. If you have another drivetrain as a point of reference, this tool is great for finding the optimal 1x chainring for your needs.  

 

In general, stock 32t and 42t chainring sizes are good, but I think many riders will enjoy riding more with a smaller ring. Don’t be swayed by macho racers pushing pie plate-sized rings. It may require some experimentation. Luckily they’re not too expensive, so try a few and find what works best for you! 

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