Mountain Bike Front Chainring Size Options & Tips/Tricks
Mountain bike chainrings are one of the vital components of your bike drivetrain. They are responsible for transmitting crank force from the pedals to the rear wheel. For optimum drivetrain and shifting performance, it is essential to fit the right chainring onto your bike. Chainrings come in a wide variety of forms and sizes. In this article, we delve into mountain bike front chainring size options to help you the right one for your bike.
A 32T chainring has 32 teeth. Standard Mountain bike front chainring size options are 32T, 34T, 36T, and 38T for both recreational and pro racers. Choose a 32T chainring for a 29er, a 36T chainring for a 26er, and a 34T for a 27.5” wheel bike.
The mountain bike crankset consists of chainrings and crankarms. The bike pedals attach to the crankarms, which attach to the chainring. Together, they convert your pedaling force to rotate the cassette and rear wheel and propel the bike forward. According to this research paper from the Sports Medicine journal, the invention of various shoes, accessories, and pedal designs continue to help enhance the speed and efficiency of pedaling. You can check out our article on how to choose mountain bike toe clip compatible shoes to maximize your riding experience. To further improve pedaling efficiency, read our guide to choosing bike pedals for grip maximization.
What is a Mountain Bike Chainring?
Mountain bikes typically have between one to three chainrings. The higher the number of rings, the wider the range of gears available. Chainrings have teeth that are evenly spaced for chain links to engage with or slot onto. The number of teeth can range anywhere from as little as 20 to as many as 60 and more. As the rider turns the pedals, the crankarms rotate. This, in turn, rotates the chainring, which pulls the chain. The chain then powers the drivetrain by using the pedaling force to spin the cassette and rear wheel.
A mountain bike chainring is a cog in the bike drivetrain that helps transfer energy from the legs to the bike. It has distinguishing features such as shape, material, and tooth profiles.
Chainrings like these typically have chain ramps or pips, which act to help the bike chain during shifting. They prevent the chain from getting stuck between the crankset components when shifting from an outer to an inner ring. Chainrings also come with bolt holes where the chainring bolts fit to screw the chainring to the cranks. The number of holes could be either four or five. This varies the bold center diameter (BCD), which determines the compatibility between a crank and chainring as explained in this article by Wolf Tooth.
The crankset your bike has, also determines how the chainring is replaced. Some cranksets have removable bolt-type chainrings to allow for separate replacements. Others have chainrings welded to the crankarm as an integrated mount set. This way, to replace the chainrings, you’ll have to replace the entire crankset.
How to Choose the Right Type of Mountain Bike Chainring
There are several factors to consider when choosing the chainring to purchase for your mountain bike. You may want to replace your chainrings, upgrade them, or experiment with some new models. If your chainrings are worn, you’ll begin to experience problems like chain suck, chain drop, and faulty gear shifting. In that case, it would be better to replace the chainring. Our article on how to replace a mountain bike chainring will walk you through the entire process. Worn chainrings might also indicate that the chain is worn. You can read over our comprehensive guide on how to replace a chain on a mountain bike to learn more.
Regardless of your reason, it is important you select the right type of Mtb chainring.
Oval vs. Round Chainrings
Oval chainrings like this differ from traditional chainrings like this in that they have an elliptical rather than the standard circular shape. Round chainrings have a consistent gear ratio as you pedal due to the consistent radius. On the other hand, the radius of oval chainrings changes as you pedal, changing the gear ratio. The smaller radius section allows for easier pedaling while pedaling gets harder with the larger radius section. With round chainrings, the power delivery is pulsating while, with oval chainrings, the power delivery is more even and constant.
One main benefit to oval chainrings is that pedaling through the dead stroke is easier. According to this study, by the Biomechanics of Cycling, pedaling is weakest when the pedals are at a vertical plane between the 90 and 110-degree points of the crank cycle. Oval chainrings offer a smoother and easier transition of the front chainring teeth to the chain links when pedaling through those vertical dead spots. The chainrings are specially optimized for low cadence pedaling. At high cadence, riding with oval chainrings is less efficient and less comfortable as you’re not moving as smoothly. You can fit on clipless pedals to minimize this problem. Check out our article on the benefits of clipless pedals to discover more about this pedal system.
While the oval chainring has its advocates, there has been no conclusive evidence of a significant increase in efficiency or power output, as this independent study by Biomech Non-Circular Dynamics discusses. In addition, this research by the Journal of Sports Science and Medicine found only minor differences in power output, heart rate, and oxygen consumption between riders that use oval and round chainrings. However, according to this Mountain Bike Reviews forum thread, many riders note that oval rings help with joint pain and make climbing hills and long rides easier and more comfortable.
Aluminum Vs. Steel Chainrings
The main difference between aluminum and steel chainrings is in terms of durability and weight. Both steel and aluminum look identical and perform with similar efficiencies. However, the lifespan of steel rings is longer than aluminum rings as steel is more resistant and durable than aluminum. Steel rings typically bend when they fail. And they can usually be safely bent back into shape as long as the deformation is not too severe.
This feature is particularly important for 1x drivetrains, which make use of only one chainring with all the gears on the rear cassette. According to this article by Velonews, although 1x drivetrains are lighter and offer simpler gearing, they result in higher frictional losses. They also lead to increased chain wear as the chain has to bend at exaggerated angles to access the largest and smallest rear cogs. In addition, because only one chainring has to bear the burden of every pedal stroke, there is more pressure on the ring. In this case, a chainring with steel construction is more suited to making a long-lasting drivetrain.
On the other hand, aluminum is much lighter (about 2.9 times) than steel, according to this research paper on the Comparative Analysis of Steel and Aluminum Structures, conducted by the Faculty of Civil Engineering, Architecture and Geodesy at the University of Split. For riders who want to reduce weight, an aluminum chainring would be the preferred option. However, as this study by the International Journal of Lightweight Materials and Manufacture discusses, aluminum materials are usually costlier than their steel counterparts. This 104 BCD aluminum chainring has a weight of 0.15 pounds, while this 104 BCD steel chainring weighs 0.47 pounds, more than double the weight.
Aside from the construction of your chainrings, you may also be interested in the type of mountain bike to purchase based on the construction. Our article on carbon mountain bikes vs aluminum compares the two and other frame materials to help you determine which is best for you.
Why Chainring Tooth Profiles Matter
The size of a mountain bike chainring is usually indicated by the number of teeth on the ring. Your chainring size will vary depending on your riding terrains and other factors. Apart from the obvious weight difference, as the number of teeth increases, the gear ratio increases. This means larger rings will have high gear ratios and be harder to pedal through. On the other hand, smaller rings give lower resistance and gear ratios, allowing for easy pedaling. As a result, the different sizes are suited for different riding preferences and conditions.
Smaller chainrings like this wear the drivetrain faster and cause chain drop more easily but are more suitable for climbing and long rides. Bigger chainrings like this are more suitable for fast descents and aid speed on flat terrains.
According to this research paper by CeramicSpeed, bigger chainrings are more efficient than smaller chainrings given the same effective final gear ratio as they allow for decreased frictional losses. This is due to decreased tension in the chain and decreased articulation angle. As a result, the chain does not articulate as much when wrapping around the chainring, thus reducing friction and increasing drivetrain efficiency.
Gear shifting that is faulty or difficult could signify worn or faulty chainrings. If you're experiencing this problem, take a look at our article on how to fix a mountain bike chain that's jumping gears or skipping, which provides an in-depth guide to diagnosing and fixing this issue.
Summary of How to Decide on the Best Mountain Bike Front Chainring Size for You
| What problems do you have while biking? | Could a new mountain bike front chainring size help? | What size will help and why? | Example: |
| I want to ride faster on uphills | Yes | Buy a smaller chainring size like a 32t or 34t | Wolf Tooth Mtb Chainring |
| I want to ride faster on downhills | Yes | A larger chainring size increases speed on descents so choose a 36t or 38t | Xt Shimano Chainring |
| My bike is too heavy | Yes | Smaller chainring sizes are considerably lighter than larger rings so buy a 32t | Truvativ Mtb Chainring |
| I want to ride faster on flat terrains | Yes | Fitting a larger chainring size like a 36t or 38t will help maintain top-end speed | Shimano Dura Ace FC |
| I want a more comfortable long-distance ride | Yes | Smaller chainrings are better for long rides since they make pedaling easier, so choose a 32t or 34t | Sram Unisex X-sync Chainring |
Standard Mountain Bike Chainring Sizes
Most bike manufacturers fit their mountain bikes with a 32 or 34-tooth chainring. The chainring size determines the gear range available for use on your terrain. You can easily change your chainring and fit a larger or smaller chainring size as needed. However, there must be enough tire clearance for the chainring.
Mountain bike chainring size options are 32T, 34T, 36T, and 38T.
In addition, you must consider compatibility issues with respect to the number of bolt holes, bolt circle diameter, and the number of teeth. The ideal chainring size for you depends on your local trails and terrains and your type of bike.
One factor to consider when choosing the size chainring is your cadence. Cadence refers to the pedal rate – the number of revolutions of the crank per minute and influences power outputs and energy consumption, according to this article by the International SportMed Journal. Some riders prefer to pedal at high cadence, while others prefer slower pedaling cadence. Depending on your preferences, the gear combination and chainring size will vary. For high cadence, a smaller chainring is preferable, while for low cadence, a larger chainring will work better.
Here we list the different front chain ring sizes that are available:
A 32 Tooth Chainring
A chainring with 32 teeth like this has a diameter of 144.2 mm (5.69 inches). Fitting a 32T chainring is usually best for beginner riders. This is because the chainring gives a lower gear ratio which is easier to push. For beginners who have not perfected their pedaling technique, this can make a lot of difference and make riding much more comfortable. In addition, a 32T chainring feels lighter and has little resistance to pedaling, requiring smaller effort to spin the chainring.
A 34 Tooth Chainring
34-tooth chainrings like these have a diameter of 144.2 mm (5.69 inches). They are particularly suitable for steep terrains. The easier gear combination allows for easier uphill climbing. In addition, for suspension mountain bikes, a 34T chainring helps to increase anti-squat. Anti-squat refers to the suspension's resistance to compression caused by the rider pedaling and weight transfer while pedaling. As you pedal, the chain is pulled forward, creating tension and force on the suspension system, which is the anti-squat. You can watch this YouTube video tutorial for more information and an easy-to-follow demo.
34T chainrings help to increase anti-squat, which eliminates the pedal-induced compression, allowing for more energy to be translated to forward movement. It firms up the rear end, lifting the rider's weight for efficient climbing. This lets you pedal through places you would have gotten stuck in with larger chainrings. The chainring also helps make longer endurance rides less tiring as it is optimized for lower cadences, saving energy and reducing knee strain.
A 36 Tooth Chainring
With 36-tooth chainrings like these, riding on flat terrains is much easier. The diameter of the ring is 152.2 mm (6.01 inches) and if you're riding in mostly flat areas, you'll be better off with a larger 36T chainring. This is because the chainring allows for higher and more consistent speeds on those terrains.
Fitting a 36T chainring with a small sprocket will give a high gear combination, which makes it harder to pedal but faster on flat terrains. It is also great for bikes with small wheels. A 36T chainring also allows for faster descents and more control when riding downhill. It prevents you from spinning out on fast downhills. To help protect your body while riding downhill, check out our tips and tricks for buying downhill mountain bike armor.
A 38 Tooth Chainring
This chainring has a diameter of 160.3 mm (6.33 inches). For pro-riders and bikes meant for racing, 38-tooth chainrings like these or bigger are usually preferred. They are great for maintaining higher top-end speeds and are also more efficient as they reduce friction loss due to chain articulation. Although the increased efficiency is small, it makes a difference for pro-racers. Pro-riders usually have better pedaling techniques and so can handle the harder gears efficiently as well.
How to Decide Between a 32T or 34T Chainring
32T and 34T chainrings are the industry standards usually fitted on mountain bikes. They provide the best balance for riding mountain bikes, assisting with shifting up steep terrains and heavy loads. However, if you're a beginner and prefer a lighter bike, then a 32-tooth chainring might be preferable. On the other hand, if you spend a lot of time riding steep terrains and are looking for a larger chainring with easier pedaling, then you might want to try a 34-tooth chainring.
How to Decide Between a 32T or 36T Chainring
A 32T chainring gives a lower gear ratio, while a 36T gives a higher gear ratio. As a result, a 32T chainring is much easier to pedal than a 36T chainring as they offer less resistance. 32T chainrings are more suitable for steep terrains and long rides, while 36T chainrings are better for descending fast and flat terrains. With the bigger 36T chainring, there is less chance of the bike chain slipping off. Another cause of chain slip is a bike chain that's too long or loose. If you discover this to be the case, our articles dealing with a mountain bike chain that's too long and how to tighten a mountain bike chain will come in handy.
If you prefer a lighter chainring and easier pedaling, then a 32T chainring is the one for you. On the other hand, if you don't mind the extra weight but need the harder gears and higher speed, then go for a 36T chainring.
| Chainring | When To Use | Example | Price |
| 32T | Novice biker | Shimano M590 Chainring | ~$20 |
| 34T | Steep Terrain | Fsa Pro Chainring | ~$30 |
| 36T | Flat Terrain | Sram Blatt Schutz Mtb Chainring | ~$30 |
| 38T | Maximum speed | Shimano Dura Ace FC | ~$35 |
When to Use a Smaller Chainring on a Mountain Bike
Deciding to use a smaller chainring depends on your riding preferences and conditions. Although smaller chainrings wear out the drivetrain faster and cannot go as fast as larger rings, they have a lot of benefits and might be just what you need.
Use a smaller chainring on a mountain bike when climbing is a struggle, the terrain is steep, or there is extra weight on the bike.
Here we list reasons to use a smaller chainring:
Reason 1. Climbing is a Struggle
Smaller chainrings are great for climbing uphill. If your local terrain requires a lot of climbing, fitting a smaller chainring on your bike would be the best option for you. Riding with a larger chainring will be difficult and tiring as the pedals are harder to push and the anti-squat is less. You might even be forced to get off and hike instead. On the other hand, smaller chainrings come with a lower gear ratio allowing for easier gearing. The extra torque lets you conquer and power through uphill climbs.
Reason 2. The Terrain is Steep
Another scenario where a smaller chainring is needed is with steep terrains. Steep terrains are one of the hardest trails to adapt to for riders. However, with smaller chainrings, the terrain is less challenging and daunting. The easier pedals keep your legs fresh and help you tackle those harder trails. Compared to larger chainrings, smaller ones make riding rough and technical terrains easier and smoother. With smaller chainrings, you have improved comfort and less pedaling resistance. Smaller chainrings also increase anti-squat on your bike. For these reasons, they’re more suited for steep terrains than larger chainrings.
Reason 3. Extra Weight on the Bike
Smaller chainrings are obviously lighter than larger chainrings. They have fewer teeth, a smaller diameter, and weigh less. As a result, they’re not only great for heavier bikes but also when carrying extra weight on the bike. If you’re camping and securing a heavy backpack on your bike, fitting a larger and heavier chainring might weigh you down and make riding uncomfortable. You can lose all that extra weight by using a smaller chainring instead.
Making use of a smaller chainring could be beneficial if you’re taking along a heavy tool bag. In that case, we suggest you read our article on how to fix a mountain bike tool bag that’s heavy.
When to Use a Bigger Chainring on a Mountain Bike
Bigger Chainrings are also suited for different riding preferences and conditions. While they’re unsuitable for climbing or particularly long rides, they can help in other instances.
Use a bigger chainring on a mountain bike when higher speed is needed, or more efficiency is required on flat terrain.
Here we list reasons to use a larger chainring:
Reason 1. Higher Speed is Needed
Elite mountain bike racers typically prefer bigger chainrings due to the higher top-end riding speeds. Although the gears are harder, the chainrings are more efficient than smaller ones. In addition, larger chainrings are easier to control. Rather than spinning out on downhill rides, larger chainrings allow for lower cadence and a higher level of control. However, using a smaller chainring would be preferable if you don’t need the extra efficiency or faster speed.
Reason 2. More Efficiency on Flat Terrain
This research paper by CeramicsSpeed, that we have already mentioned, showing the results of testing the effects of chainring size on drivetrain efficiency concluded that a larger chainring creates less frictional losses than a smaller one, given the same gear ratio, power output, and cadence. With larger rings, the top-span chain tension is decreased. As the chain engages the chainring and disengages the rear cog, the articulation angle is also decreased. There is also an increased articulation rate. These factors decrease the chain articulation, thereby leading to an overall reduction in frictional losses.
As a result, the larger chainring is more efficient than the smaller one. This is especially true on flat surfaces where larger chainrings can sustain top-end speed better than smaller chainrings.
How to Choose Your Chainring Size
The first step in choosing your chainring size is to determine your riding preferences, terrains, and conditions. As discussed above, these factors will dictate whether you should fit a smaller or a larger chainring on your mountain bike. Other factors you need to consider when choosing a chainring size include the number of teeth and bolt holes on your chainring and the bolt center diameter. These factors are necessary for optimum compatibility with the crankset. When fitting a new chainring, you may want to install a guide to prevent chain slip and ensure that the chain stays in place as our mountain bike chain guide installation instructions suggest.
This video tutorial by Full Speed Ahead explains a little more about choosing chainrings for your mountain bike.
Another factor that helps when choosing a chainring size is the gear ratio. Knowing how to get the gear ratio will help you compare different gears on your bike and different chainring and cog options. You’ll also be able to determine how fast you’ll travel in a particular gear at a specific cadence. With this knowledge, you’ll be able to experiment with different chainrings till you work out the best setup for your mountain bike.
You can do the calculation yourself. To get the gear ratio, simply divide the number of chainring teeth by the number of cog teeth. For instance, suppose you have a chainring with 32 teeth and a cog with 16. The gear ratio will be 2:1. This value calculates the cadence. For each crank revolution, the wheel will turn two times.
The gear inches indicate the effective diameter of the wheels. It gives the diameter of the rear wheel of a penny-farthing bicycle with the same gearing. To get the gear inches, follow this process: Multiply the gear ratio by the bike’s wheel diameter. With our previous 32/16 gearing and a classic 700x28c setup with a wheel diameter of 26.69 inches, the gear inches will be 53 inches (to the nearest inch).
To get the gear development, the distance you’ll cover in a given gear at a specific cadence, follow this process: Multiply the gear inches by pi (3.14) and convert to metric. With the previous values, the gear development would be 4.23 meters for the 700x28c setup and 32/16 gearing.
You can then try out different gearing values and setups to check for the range of gears available on your bike.
You can also make use of an online gear calculator like this from Sheldon Brown. Once you enter your values, the calculator gives you a gear chart with the necessary values. Alternatively, you can make use of mobile apps on Android and iOS devices like the Bike Gear Calculator. They have interactive user interfaces that allow you to set your different values and they perform all the calculations for you. You can get the app on Google Play Store or Apple App Store.
