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MTB Bike Cranks Selection: What Riders Need to Know

MTB bike cranks are a critical component of a mountain bike’s drivetrain, responsible for transferring the power generated by the rider’s pedaling to the bike chain and, ultimately, to the wheels, propelling the bike forward. In this guide, we’ll explore the key aspects of MTB bike cranks—including their structure, sizing, materials, and important factors to consider when purchasing. This information will help you choose the right and most efficient MTB bike cranks for your mountain biking needs.

What Are MTB Bike Cranks?

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MTB bike cranks, also known as the bike crankset or bike chainset, are not a single structure but a combination of several essential parts. These include the crank arms, chainring(s), spindle, and bottom bracket, with each component playing a vital role in the overall functionality of the drivetrain.

  1. Crank Arms: These are the two arms that extend from the bottom bracket (the axle area of the bike) to the pedals. Crank arm lengths typically range from 165mm to 175mm, which affects leverage, ground clearance, and pedaling efficiency.
  2. Chainrings: Chainrings are the toothed, circular components that engage with the bike chain. They are usually mounted on one side of the crankset and come in single, double, or triple configurations (1x, 2x, or 3x). Each setup has its benefits:
    1x (Single Chainring): Popular for its simplicity, low maintenance, and lightweight.
    2x (Double Chainring): Provides a broader gear range, ideal for varying terrain.
    3x (Triple Chainring): Offers the widest gear range but is less common in modern mountain bikes due to its weight and complexity.
  3. Spindle: The spindle is the axle that connects the two crank arms through the bottom bracket, allowing them to rotate. The size and compatibility of the spindle vary, so it’s important to ensure the crankset fits your specific MTB’s bottom bracket.
  4. Bottom Bracket: Although not technically part of the crankset, the bottom bracket connects and supports the cranks within the bike frame. It allows the crankset to rotate smoothly and bears much of the rider’s weight.

MTB bike cranks are a specific type of bike cranks, designed exclusively for mountain bikes (MTBs). Due to the unique demands of mountain biking—such as enhanced durability, adaptability to rough terrain, and the need for better ground clearance—MTB bike cranks are structured and configured differently from those used on road or city bikes. As a result, they are not interchangeable with cranks designed for other types of bicycles.

How to Choose the Right MTB Bike Cranks?

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Below, I’ll address some of the most frequently asked questions from riders to highlight key factors to consider when purchasing MTB bike cranks, including crank size, material, and chainring setup options.

What Size MTB Bike Cranks Do I Need?

Next, I’ll address some common questions from riders to highlight the key factors to consider when purchasing MTB bike cranks. This includes the size, material, and configuration options for crank arms, chainrings, spindle, and bottom brackets.

Crank Arm Length

When selecting the right MTB bike cranks, one of the most crucial factors to consider is the crank arm length. The ideal length varies based on your leg length, riding style, and the terrain you ride on. Here’s a breakdown of key considerations:

  1. Leg Length and Crank Arm Size: Traditionally, the longer your legs, the longer your crank arms should be. Taller riders generally opt for 175mm crank arms, while shorter riders may find 165mm or 170mm cranks more comfortable. Matching your crank arm length to your leg length ensures a more efficient and comfortable pedal stroke.
  2. Riding Style: Your riding type plays a significant role in choosing the correct crank arm length:
    • Technical Trail Riding: If you’re frequently riding on rocky or uneven terrain, shorter crank arms (165mm-170mm) provide better ground clearance. This helps prevent pedal or crank arm strikes on obstacles, which is essential for technical MTB riding.
    • Climbing and Endurance Riding: Longer crank arms (175mm or more) are better suited for climbing steep hills or endurance rides. Longer cranks offer greater leverage, making it easier to push through tough climbs or maintain a steady cadence over long distances.
  3. Ground Clearance: One of the main advantages of shorter crank arms (like 170mm) is the added ground clearance, reducing the chances of pedal strikes on uneven surfaces. This is especially important when riding technical MTB trails. A crank arm length of 170mm is a popular choice as it strikes a good balance between pedal clearance and pedaling efficiency.

Chainring Size

Choosing the right chainring size is a crucial decision that directly impacts your MTB bike’s performance, particularly in terms of pedaling efficiency, gear ratios, and overall riding experience. The size of your chainring determines how easily you can pedal, climb hills, and achieve top speeds on different terrains. Here’s a detailed guide on how to choose the appropriate chainring size:

1. Gear Ratios

The gear ratio is determined by the number of teeth on the front chainring and the rear cassette. A higher gear ratio (larger front chainring and smaller rear cog) allows for faster speeds on flat or downhill terrain, while a lower gear ratio (smaller front chainring and larger rear cog) makes it easier to climb steep hills or ride on rugged trails.

  • Higher Gear Ratios (Larger Chainrings): These chainrings (e.g., 34T, 36T) are best for fast riding on smooth, flat terrain or downhill trails, where maintaining speed is key. They require more effort to turn the pedals but are ideal for riders looking for higher speeds and less effort on flat or descending trails.
  • Lower Gear Ratios (Smaller Chainrings): Smaller chainrings (e.g., 30T, 32T) are designed for challenging terrains like steep climbs or technical trails. They reduce the pedaling effort, allowing riders to more easily tackle uphill sections or rocky paths without overexerting themselves.
2. Chainring Size and Compatibility

When selecting a chainring, it’s crucial to ensure it’s compatible with your bike’s crankset. Chainrings are typically mounted using one of two systems: a direct mount system or a BCD (bolt circle diameter) system.

  • Direct Mount System: In this system, the chainring is directly attached to the crankset without the need for bolts or a separate mounting ring. It’s a simpler and more streamlined design, often found on modern mountain bike cranksets.
  • BCD System: BCD refers to the bolt circle diameter, which is the diameter of the circle formed by the bolts that attach the chainring to the crankset. The chainring has holes that align with the bolts on the crankset, and the BCD size (usually measured in millimeters) needs to match the crankset’s bolt pattern for proper installation.

Each system has specific compatibility requirements, so be sure to verify that your crankset supports the type of chainring you choose.

Narrow/Wide Teeth Design: Most modern 1x MTB chainrings feature a narrow/wide tooth design, where alternating wide and narrow teeth help secure the chain in place, improving chain retention. This is particularly important for riders on technical trails, where chain drop can be an issue. The design ensures a more stable chain, reducing the risk of it coming off during rough rides.

3. Choosing the Right Chainring Size Based on Terrain
  • Cross-Country (XC) Riders: If you primarily ride on smooth trails or cross-country terrain, a larger chainring (32T–36T) paired with a wide-range cassette will allow you to maintain speed and efficiency over long distances.
  • Trail and Enduro Riders: If your trails are a mix of moderate climbs and technical descents, a mid-range chainring (30T–34T) would provide a good balance of climbing efficiency and speed on flat sections.
  • Downhill and Technical Trail Riders: For steep climbs and rough, technical terrain, a smaller chainring (28T–32T) is ideal, giving you the low gearing needed to tackle challenging uphill sections or rocky paths.

Spindle Length

The spindle length refers to the distance between the center of the bottom bracket and the center of the pedal axle, essentially the length of the spindle that extends from the bike’s frame. It plays a crucial role in determining the bike’s crankset position and affects how the bike feels when pedaling. Here’s how to determine the ideal spindle length for your MTB bike:

1. Factors to Consider When Choosing Spindle Length
  • Rider’s Leg Length and Pedaling Style: The spindle length directly impacts the Q-factor. For riders with wider hips or a preference for more stability, a wider Q-factor might be more comfortable. If you are looking for a more efficient pedaling stroke or want to reduce strain, a narrower Q-factor may be better suited.
  • Bike Type and Riding Style: Different riding styles require different spindle lengths:
    • Cross-Country (XC) Riders: Typically prefer a narrower Q-factor, which can be achieved with a shorter spindle. This allows for a more efficient pedal stroke and better clearance for fast, smooth terrain.
    • Trail and Enduro Riders: A slightly wider spindle may be more suitable for riders who require more stability on technical trails and need more room for maneuvering.
    • Downhill Riders: A wider spindle may also be preferred for added stability and better bike handling on rough terrain.
  • Crank Arm Length: The spindle length often works in conjunction with the crank arm length. A longer crank arm will need a corresponding spindle length to ensure proper pedaling geometry.

Tip: The Q-factor is the horizontal distance between the pedals when they are installed on the bike. It is influenced by the spindle length and crank arm width.

2. Standard Spindle Lengths
  • Spindle lengths typically range from 68mm to 83mm for mountain bikes, with the most common being around 68mm or 73mm.
  • 68mm spindles are often used for bikes with a more traditional bottom bracket setup, while 73mm spindles are slightly wider and provide more clearance for riders using a wider Q-factor or needing more space for pedaling.
3. Bottom Bracket Compatibility

When choosing the spindle length, you must also ensure that your spindle length is compatible with your bottom bracket. Different bottom brackets have specific spindle lengths based on their design and intended bike type. Some bottom brackets also have adjustable spindles, allowing you to fine-tune the fit.

Bottom Bracket Width

The bottom bracket width refers to the distance between the two bearings in the bottom bracket, which determines how far the crankset sits from the bike frame. This width plays a critical role in determining the bike’s Q-factor, the horizontal distance between the pedals, and affects pedaling efficiency and comfort.

1. Check Your Bike’s Specifications

The easiest way to determine the right bottom bracket width is to check the specifications of the current crankset and bottom bracket installed on your bike. Most bike manufacturers follow specific standards for bottom bracket designs, and these may vary depending on the frame and crankset brand.

If you are considering upgrading or switching brands, it’s essential to ensure the new bottom bracket is compatible with the existing crankset and frame. Bike manufacturers often set limits on the type of bottom bracket you can use, so understanding these specifications is crucial.

2. Standard Bottom Bracket Sizes

The most common bottom bracket axle diameters are 24mm and 30mm. These are widely compatible with most cranksets, and selecting a bottom bracket that matches your crankset’s axle diameter is usually sufficient for most riders.

However, some bike brands use proprietary axle sizes, which means you may need to choose a bottom bracket that is specifically designed for that brand or model. For example, brands like Race Face or Shimano have their own specific axle standards.

3. Compatibility with Third-Party Bottom Brackets

For most conventional cranksets, as long as the axle diameter matches, you can use third-party bottom brackets. However, always check the compatibility between your crankset and bottom bracket to avoid issues with installation.

Which Material is Best for MTB Bike Branks?

The material of MTB bike cranks plays a crucial role in determining their performance, weight, durability, and cost. Here’s an overview of the most common materials used in cranksets.

  1. Aluminum Cranks:
    Aluminum cranks are the most common and offer a good balance between weight, strength, and cost. They are typically the most affordable option and are durable enough for most types of mountain biking. However, they tend to be heavier compared to other materials and may flex slightly under high loads. Higher-end aluminum cranks often use advanced forging techniques to align the grain structure and reduce weight.
  2. Carbon Fiber Cranks:
    Carbon fiber cranks are much lighter and stiffer than aluminum, making them an excellent choice for riders looking to reduce weight and improve pedaling efficiency. Carbon fiber provides better power transfer, reducing flex and enhancing responsiveness, especially during technical rides and when navigating obstacles. However, carbon cranks are more expensive than aluminum, and while they offer superior performance, they are more prone to damage from impacts, especially in rocky or aggressive riding conditions.
  3. Steel Cranks:
    Steel cranks are highly durable and typically more affordable than aluminum or carbon options. They can withstand significant impact and are great for riders who prioritize durability over weight. However, they are much heavier, which can negatively affect performance, especially in competitive riding.
  4. Titanium Cranks:
    Titanium cranks are incredibly strong and lightweight, making them the premium choice for high-end mountain bike cranksets. Titanium provides excellent durability and stiffness, offering superior strength and efficiency. However, the cost is much higher than aluminum or even carbon, and many riders may not notice a significant performance difference compared to high-quality aluminum cranks.

When selecting the right material for your MTB bike cranks, it’s important to consider both the type of terrain and your riding style. For cross-country (XC) riding or racing, carbon fiber cranks are ideal due to their light weight and stiffness, which enhance power transfer and efficiency on smooth, long trails. However, for downhill riding, aluminum or steel cranks are often a better choice, as they provide superior impact resistance and durability on rocky and rugged terrain, reducing the risk of damage from collisions compared to carbon fiber cranks.

Should I Choose a 1x, 2x, or 3x MTB Bike Crank?

Choosing between a 1x, 2x, or 3x MTB crankset is a common dilemma for riders, and the right choice ultimately depends on your riding style, terrain, and personal preferences. Each setup offers distinct advantages in terms of gear range, simplicity, and performance. Here’s a breakdown of their key differences and when each might be the best fit for your mountain biking needs:

1x MTB Crank (Single Chainring)

  • Advantages: Simplified drivetrain, lighter, less maintenance, and improved chain retention with the narrow/wide tooth design. The 1x system has become the industry standard due to its simplicity and efficiency. With larger rear cogs (up to 52 teeth), the 1x system provides a wide range of gears, making front derailleurs unnecessary.
  • Disadvantages: Fewer gear options with larger gaps between gears.
  • Best For: Riders on technical trails, cross-country, and those seeking a simpler setup with enough gear range for most terrains.

2x MTB Crank (Double Chainring)

  • Advantages: Provides a wider gear range and smoother transitions between gears, offering more control over cadence.
  • Disadvantages: Requires a front derailleur, adding complexity, weight, and maintenance.
  • Best For: Mixed terrain riders who prefer a broader range of gears but don’t mind the added complexity.

3x MTB Crank (Triple Chainring)

  • Advantages: Offers the widest gear range, ideal for steep climbs and extreme terrain with significant elevation changes.
  • Disadvantages: Heavier, more complicated with a front derailleur, and higher maintenance needs.
  • Best For: Riders on very varied or mountainous terrain who need an extensive range of gears for all types of climbs and descents.

Conclusion

Overall, purchasing a new MTB bike crank isn’t as simple as just clicking “buy” and installing it. Size and compatibility are key factors to consider, followed by your personal preferences and riding needs. The easiest way to start is by checking your bike’s current crankset size. If you’re unsure about trying a new crank, it’s a good idea to consult a professional mechanic, as installation can be more complex than it seems.

FAQ

Is MTB bike crank size universal?

No, MTB bike crank sizes are not universal. Common MTB crank sizes are 165mm, 170mm, and 175mm. The crank size depends on factors like the bike frame and bottom bracket interface. It’s important to check your bike’s technical specifications to ensure the new MTB bike cranks are compatible with your setup.

Are shorter cranks better on MTB?

Shorter cranks can be better for MTB, especially on technical terrain. They offer increased ground clearance, reducing the risk of pedal strikes, and can improve bike handling. However, the choice depends on your riding style and personal preference.

How to choose an MTB crankset?

To choose an MTB crankset, consider factors like crank arm length, chainring size, and compatibility with your bike’s bottom bracket. For technical trails, a 1x setup with a narrow-wide chainring is ideal for simplicity and chain retention. Choose crank material based on your riding style—carbon for lightweight performance or aluminum for durability. Always ensure the crankset fits your bike’s specifications.

How do I know my crank size?

To measure the crank arm length, measure from the center of the bottom bracket spindle to the center of the pedal axle. Of course, you can also ask your local bike mechanic for advice.

Can I put a road crankset on a mountain bike?

Yes, you can install a road crankset on a mountain bike, but you must ensure compatibility with the bottom bracket, spindle, and chainring sizes. Additionally, consider the gearing and terrain differences between road and mountain biking.

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