How Do I Know if My Bike Has a One-Piece or a Three-Piece Crank?

The type of crank on your bike is crucial for maintenance, upgrades, and repairs. Why does it matter, you ask? Each design has its own advantages and challenges. So let's find out! 

What is a Crank? 

The crankset, consisting of the crank arms, chainrings, and sometimes the spindle, is fundamental in converting leg movement into the bike's motion.

The main part is the crank arms that are attached to the pedals on one end and the chainrings on the other. The chainrings are toothed disks that drive the chain. These two components primarily link the biker to the bike's drivetrain.

Types of Bike Cranks

Cranksets are mainly categorized into one-piece and three-piece. One-piece cranks, or "Ashtabula" cranks, are a single metal piece, common in vintage and entry-level bikes. Three-piece cranks consist of separate crank arms and a spindle, offering higher performance and are found in modern bicycles.

  • One-Piece Crank: has a continuous, curved design. The crank and the spindle are a single metal piece that curves in an S-shape that forms both crank arms and the axle that passes through the bottom bracket. The pedals are screwed directly into the crank arms. They also only use a specific type of bottom bracket that is typically a larger, cup- style that is threaded directly into the bike frame. It doesn't have a separate bolt or bearing on the outside of the bottom bracket-shell - just a large nut or cap that holds the crank in place.

    It is most commonly found on older bicycles, children's bikes, some cruisers, and lower-end BMX bikes.
One Piece Crank old photo
  • Three-Piece Crank: Three-piece cranks have two separate crank arms and a spindle. The crank arms attach to the spindle, w/c then fits into the bottom bracket bearings. It has bolts at the junction of the crank arms and the spindle. The pedals are attached to the arms via threads that are part of removable arms, not directly into the integrated spindle. With this, easier changes and upgrades can be done to the crank arms or pedals.

    They are compatible with several types of bottom brackets, but most commonly, they use a sealed bearing system. The spindle, which separate piece from the arms passes through these bearings. They are usually outside the frame's bottom bracket shell w/c are not present in one-piece crank set ups. These cranks are most common on modern bikes. 
Wide Crank Assembly w/ Extended Bottom Bracket Assembly

Advantages and Disadvantages

Simplicity Fewer parts, reliable for casual riding Versatile, compatible with many frames
Durability Sturdy, good for children's bikes and some BMX High performance, handles stress
Cost-Effective Budget-friendly Customizable
Compatibility Limited compatibility with modern bikes More complex to install and maintain
Weight Heavier More expensive
Upgradability Difficult to upgrade components Requires more frequent maintenance


How to Choose the Right Crank for Your Bike?

Choosing the right crank for your bicycle depends on a lot of factors  which includes your bike type, riding style, and maintenance preferences. Here are some considerations to help you make that choice:

Consider Your Bike Type

  • Bike Frame Compatibility: Make sure that the crank you choose is compatible with your bike frame’s bottom bracket. Modern frames mostly require three-piece cranks.
  • Purpose of the Bike: What will you use your bike for? If it’s for casual or children’s bikes, a one-piece crank might suffice. For more rigorous activities like mountain biking or road racing, a three-piece crank would be more appropriate due to its durability and performance capabilities.

Assess Your Riding Style

  • Performance Needs: If you’re into competitive riding or require high performance, three-piece cranks offer better power transfer and are sturdier under stress.
  • Casual Riding: For everyday or leisurely rides, a one-piece crank is generally adequate and offers reliability with minimal maintenance.

Maintenance and Upgrades

  • Ease of Maintenance: One-piece cranks are simpler and require less frequent maintenance, making them ideal for those who prefer a low-maintenance option.
  • Upgrade Flexibility: If you foresee wanting to upgrade parts of the crankset, such as the chainrings or crank arms, opting for a three-piece crank will provide more flexibility.

Note that one-piece cranks are typically less expensive upfront than three-piece cranks. How much you’re willing to invest in your bike’s components? Although three-piece cranks may be more costly initially, they might save money in the long run due to their durability and the option to replace individual parts instead of the entire crankset.


Explore BikeBerry for more insights into bike parts and maintenance. Join forums, read cycling books, and consider online courses to deepen your knowledge of bicycle mechanics. Enjoy your ride!

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