The crankset is one of the most important parts of a bicycle. It is the key component that helps move the chain as you pedal. Also, it is the heart of the drivetrain.

However, what are the parts of a crankset? What makes it the core component that makes the bike move? In this article, we are going to tell you everything about cranksets.
 

Let’s get started!

Cranksets typically comprise chainrings, spiders, crank arms, spindles, and bottom brackets.

1. What are Crank Arms?

There are usually two crank arms in one bike. They connect the pedals to the bottom bracket of a bike. When you push the pedals, the crank arms spin and turn the chainring, which moves the chain and makes the back wheel go.

 

2. What is a Spider?

A few extensions coming out of the right crank arm that connect the chainrings are called spiders.
 

3. What is a Chainring?

Cranksets usually have one, two, or three chainrings, depending on the bike's design and purpose. The number of the crankset's chainrings will decide your bike's gearing.
 

4. What is a Spindle?

A spindle connects the right crank arm to the bottom bracket. It is the axle that the crank arms spin around.
 

5. What is a Bottom Bracket?

The bottom bracket is the connection between the cranks and the frame. It lets them spin smoothly without turning the whole frame.


 

Crucial Specifications and How to Buy Cranksets

Crank Arms Length

Crank arms come in various lengths. They typically range from 165mm to 175mm. Road bikes commonly use 172.5mm. As for mountain bikes, they often use 170mm or 175mm. Longer cranks provide more leverage and are suitable for larger bikes. Shorter cranks support a higher pedaling cadence and are popular among triathletes.
 

Bolt circle diameter

The bolt circle diameter (BCD) is the measurement (in millimeters) of the circle that runs through the center of all the bolts on your chainring. You’ll need to know BCD if you’re replacing a bolt-on chainring. BCD determines chainring compatibility. With smaller BCDs, we use smaller chainrings. For example, a 130mm BCD fits a minimum 38t ring, while a 110mm BCD can go down to 33t. Traditional systems had different BCDs for different chainring sizes, but newer Shimano road cranksets standardize 110mm BCD for all sizes. Nevertheless, SRAM uses various BCDs depending on the crankset model, which limits cross-compatibility.
 

The Number of Chainrings

As we mentioned above, the number of chainrings varies depending on the bike's design and purpose. Conventionally, most road bikes use two chainrings. As for newer mountain bikes, they use only one chainring. The reason is that they're simple, reliable, and offer all the gears most riders need. As a result, gravel bikes and even some road bikes all switch to using only one chainring.

 

Different Bikes Different Cranksets

Crankset designs play a huge part in your riding style. Here's an overview of road, mountain, and time-trial bike cranksets.
 

Road Cranksets

Road bikes typically use double cranksets, with three main types:

  • Standard (53/39t)

    It was pretty common in the past. However, it is now mostly used by racers. Because people now tend to choose smaller chainrings. Additionally, 12-speed drivetrains make standard cranksets replaced by alternatives like Shimano's 54/40t and SRAM’s 50/37t due to gear changes. 
     

  • Semi-compact (52/36t)

    It is popular among sporty road bikes. It offers a decent balance between speed and climbing. 
     

  • Compact (50/34t)

    It is very suitable for entry-level bikes, especially great for climbing.

Other setups include 1x cranksets and triple cranksets. 1x cranksets are relatively simple, light, and more efficient. Triple cranksets are rarely seen today, mostly on touring bikes.

 

Mountain bike cranksets

Most modern mountain bikes now use a single chainring (1x setup), which makes the drivetrain simpler. They rely on wide-range cassettes in the back to give you all the gears you need. Entry-level bikes might still have double or even triple chainrings. Such as SRAM’s GX-1000 or S-200 models. Different mountain bikes have different axle widths, which means the cassette isn’t always in the same place. As a consequence, the position of the chainring (called chainline) needs to match the axle widths so that the chain runs smoothly through all the gears. To deal with this, some brands make cranksets with different chainline options.
 

Time Trial Bike cranksets

Time trial bike cranksets have used 1x cranksets for a while because they are usually lighter than 2x cranksets and can also be more efficient. Time trials often take place on flat or rolling courses. Riders will adjust their gears depending on the characteristics of the courses. As a result, riders often use larger chainrings (53 teeth or more) and closely spaced cassettes to optimize gearing.
 

Bottom Bracket

The bottom bracket connects the crankset to the bike frame, allowing it to rotate. The bottom bracket is normally threaded into a frame’s bottom bracket shell. What's more, it usually contains bearings inside, which helps rotation. Some bottom brackets have an integrated spindle, and others don’t. When the bottom brackets are worn out, we rather replace them than repair them.

There are many bottom bracket (BB) standards, which differ in bearing spacing, how they're mounted in the frame, and spindle diameter. Here is a brief introduction of the main types of BB standards.

 

BSA standard (also known as British Standard Thread or English Thread)

one of the most common BB standards in the cycling world. It is widely compatible with various types of cranksets. In addition, it is easy to replace and less likely to creak.

 

Press-Fit bottom bracket

Press-Fit bottom bracket comes in different specifications. Such as the BB30, PF30, and BB86/92. The feature of the Press-Fit bottom bracket standard is that its bottom bracket bearings are pressed directly into the frame. It is relatively light and is compatible with wider spindles.
 

DUB standard

The DUB standard is a bottom bracket and crank spindle system developed by SRAM. It is introduced to simplify and unify their bottom bracket options. 
 

Q&A

1. When should I replace my crankset?

(1)The crank arms are bent, cracked, or damaged.

(2)The chainrings are worn out.

(3)When you want to upgrade components for better performance or compatibility.

 

2. Do cranksets wear out?

Yes, cranksets can wear out over time, especially the chainrings. Dirt and grit that stick to the bicycle chain will wear away the chainring’s teeth every time you pedal.

 

3. How long does a crankset last?

It depends on how often you ride, what type of terrain you ride on, and how well you take care of your bike. For a casual cyclist who normally rides on flat terrain, the crankset might last for several years. If you're a mountain biker who rides on rough terrain, your crankset might only last for a few months.

 

4. How do I know what cranksets to buy?

The crankset is far from simple. We suggest sticking to the brand and model of the crankset that’s already on your bike if you want to avoid compatibility issues.

 

Conclusion

A crankset is a vital part of any bicycle, which transforms the pedaling power to the drivetrain. Its main components are crank arms, chainrings, spindle, spider, and bottom bracket. Which crankset is more suitable for you depends on your riding style. With many standards and options available, selecting the appropriate setup based on your bike type, riding style, and drivetrain needs is essential for getting the best performance out of your bike.