What is the Bike Chainline

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At its core, bike chainline refers to the angle of a bicycle chain relative to the centerline of the bike frame. It’s all about how the chain interacts with the front chainring(s) and rear sprocket(s). Ideally, a bike has a perfect chainline when the chain runs parallel to the centerline of the frame. This means that the rear sprocket is directly behind the front chainring.

Chainline can also refer to the distance between a sprocket and the centerline of the frame. For example, a front crankset and/or front derailleur might be designed to have a chainline of 47.5 mm. This means it will work best when the middle of the crankset is 47.5 mm from the middle of the bike center line.

Over time, different types of bikes have emerged, each with its own chainline requirements and preferences.

In the early days of cycling, chainline standards were not as defined as they are today. Bicycles had narrower frames and simpler drivetrains, and chainlines varied from one bike to another. However, as technology advanced and new bike designs emerged, the need for standardized chainline measurements became apparent.

Different types of bikes, such as road bikes, track bikes, BMX bikes, and single-speed bikes, have specific chainline requirements based on their intended use, design, and geometry. For example, track bikes require a narrower chainline to accommodate their fixed gear drivetrains, while mountain bikes may have wider chainline measurements to accommodate their wide-range cassettes.

Chainline Standards: Historical and Modern Examples

Let’s take a closer look at some historical and modern chainline standards for different types of bikes:

1. Road Bikes:

– Historical: In the past, road bikes typically had a chainline of around 43.5mm to 45mm, depending on the number of chainrings.

– Modern: Nowadays, road bikes commonly have a chainline of around 45mm to 47.5mm, again depending on the drivetrain configuration.

2. Track Bikes:

– Historical: Track bikes traditionally had a narrow chainline of around 42mm to 43mm, optimized for their fixed gear drivetrains.

– Modern: The modern standard for track bikes remains similar, with a chainline ranging from 42mm to 44mm.

3. BMX Bikes:

– Historical: BMX bikes have always had wider chainlines to accommodate their single-speed drivetrains, typically around 48mm to 50mm.

– Modern: The chainline standards for modern BMX bikes have remained relatively consistent, with measurements ranging from 47.5mm to 50mm.

4. Single-Speed Bikes:

– Historical: Single-speed bikes have varied chainline measurements depending on the specific model, but they often align with the historical standards for road or track bikes.

– Modern: Modern single-speed bikes generally adhere to similar chainline standards as road or track bikes, with measurements ranging from 43.5mm to 47.5mm.

It’s important to note that these are just examples, and chainline standards can vary depending on the specific bike model, manufacturer, and drivetrain components. Always consult your bike’s user manual or reach out to a professional bike mechanic to ensure you have the correct chainline setup for your bike.

Why Bike Chainline is Important

As a cycling enthusiast with over 10 years of experience, I can tell you that bike chainline is a crucial aspect of your bicycle’s performance. It may seem like a small detail, but it has a significant impact on your riding experience. Here in this part, we’ll explore why the bike chainline is important and how it affects your cycling journey.

1. Proper chainline can affect efficiency and smoothness of pedaling.

Have you ever noticed that some bikes feel smoother and more efficient than others? Well, one of the factors that contribute to this is the chainline. A straighter chainline reduces friction and mechanical losses, resulting in a more efficient transfer of power from your legs to the pedals. On the other hand, a crooked chainline increases drag and noise, making your pedaling less smooth and efficient.

2. Proper chainline can maintain the bicycle’s durability and reliability.

Nobody wants to deal with a chain that constantly breaks or wears out quickly. A proper chainline plays a crucial role in the durability and reliability of your chain and sprockets. When the chainline is straight, the force is evenly distributed across the chain and sprockets, reducing wear and tear. However, with a crooked chainline, the force is concentrated on certain parts of the chain and sprockets, accelerating their deterioration.

3. Proper chainline determines the compatibility and performance of your drivetrain components.

If you’ve ever had trouble shifting gears smoothly or experienced chain drop or breakage, it could be due to a misaligned chainline. A proper chainline ensures that your front and rear sprockets are aligned correctly, allowing the chain to move smoothly between them. Additionally, it ensures that your front derailleur can operate effectively, providing precise and reliable gear changes.

Now you may have a general understanding of the importance of chainline. In the following contents, we will talk about how to measure your bike chainline and how to adjust it to the ideal position.

How to Measure the Bike Chainline

Bike chainline can be measured using a simple ruler or a digital caliper. You can measure both the front and rear chainline separately, or you can measure the effective chainline by comparing the front and rear sprockets directly.

How to Measure Front Chainline

measuring chainline

To measure the front chainline, you’ll need to find the middle of your front chainring or chainring set. For single-speed or fixed-gear bikes, this is a straightforward process. Measure the distance from the middle of the seat tube or downtube to the middle of the front sprocket teeth.

But for multi-speed bikes with two or more front chainrings, things get a bit more complicated. You’ll need to measure the distance from the middle of the seat tube or downtube to the middle of each chainring. Then, take the average of those measurements. Alternatively, you can use some simple math formulas to calculate the middle of your chainring set based on your crank arm length, bottom bracket spindle length, and the number of teeth on each chainring.

The result of either method is your front chainline measurement in millimeters.

How to Measure Rear Chainline

Measuring the rear chainline requires finding the middle of your rear sprocket or sprocket set. For single-speed or fixed-gear bikes, measure the distance from the middle of the seat tube or downtube to the middle of the rear sprocket teeth.

For multi-speed bikes with two or more rear sprockets, the process is a bit more involved. Measure the distance from the middle of the seat tube or downtube to each end of your cassette or freewheel. Then, take half of that measurement. Alternatively, you can use math formulas to calculate the middle of your sprocket set based on your hub width, dropout spacing, locknut distance, and the number of teeth on each sprocket.

The result is your rear chainline measurement in millimeters.

How to Measure Effective Chainline

To measure the effective chainline, you need to compare the position of your front and rear sprockets relative to each other without regard to the centerline of the bike frame.

For single-speed or fixed-gear bikes, measure the distance between the middle of the front sprocket and the middle of the rear sprocket. If they are aligned, the distance should be zero. If they are not aligned, the distance should be positive or negative, depending on which sprocket is closer to the frame.

For multi-speed bikes with two or more front and rear sprockets, the process becomes slightly more complex. Measure the distance between the middle of each front chainring and the middle of each rear sprocket. Then, take the average of those measurements. Alternatively, you can use math formulas to calculate the effective chainline based on your front and rear chainline measurements and the number of gears on your bike.

The result is your effective chainline measurement in millimeters.

effective chainline

How to Adjust the Bike Chainline

Bike chainline can be adjusted by changing the position of your front or rear sprockets relative to the center line of the bike frame. There are different methods for adjusting the chainline depending on the type and number of gears on your bike, such as single speed, multi speed, fixed gear, etc.

How to Adjust Front Chainline

Adjusting the front chainline involves changing the position of your bottom bracket spindle. The method you choose will depend on the type of bike you have, whether it’s a single speed, multi-speed, or fixed gear.

For single speed or fixed gear bikes, adjusting the front chainline is relatively straightforward. You can use a bottom bracket with a longer or shorter spindle to achieve the desired chainline. Alternatively, you can add or remove spacers between the bottom bracket and the frame to fine-tune the alignment.

For multi-speed bikes with multiple front chainrings, adjusting the chainline becomes slightly more complex. In addition to changing the bottom bracket spindle length or using spacers, you also need to consider how this adjustment will impact your front derailleur alignment and shifting performance. You may need to make further adjustments to your front derailleur position, height, angle, cable tension, and limit screws to ensure smooth shifting.

How to Adjust Rear Chainline

Adjusting the rear chainline involves changing the position of your rear sprocket or sprocket set relative to the hub axle. As with the front chainline, the method you use will depend on the type of bike you have.

For single speed or fixed gear bikes, you can easily adjust the rear chainline by using a different rear sprocket with a different offset or thickness. Alternatively, you can add or remove spacers between the sprocket and the hub to achieve the desired alignment.

For multi-speed bikes with multiple rear sprockets, adjusting the chainline is a bit more involved. You can use a different cassette or freewheel with a different offset or thickness, or you can add or remove spacers between the cassette or freewheel and the hub. However, similar to adjusting the front chainline, you also need to consider how this adjustment will affect your rear derailleur alignment and shifting performance. You may need to make additional adjustments to your rear derailleur position, hanger alignment, cable tension, and limit screws.

How to Troubleshoot Common Chainline Problems

Common chainline problems are usually caused by improper alignment, adjustment, or maintenance of your drivetrain components. Here are some tips on how to diagnose and fix them

1. Chain Rub

One of the most annoying chainline problems is chain rub. This occurs when the chain touches the front derailleur cage or the adjacent chainring while you’re pedaling. Not only does it create an irritating noise, but it also causes friction and wear on both the chain and the derailleur. Here’s how you can fix it:

1. Adjust the position: The front derailleur should be parallel to the front chainrings and aligned with the largest ring. Make sure there’s a gap of about 1-3 mm between the outer cage plate and the largest ring.

2. Check the height: The front derailleur should be as low as possible without touching the largest ring. Again, aim for a gap of about 1-3 mm between the outer cage plate and the largest ring.

3. Fine-tune the angle: The front derailleur should be parallel to the front chainrings. If it’s not, you can rotate the derailleur slightly by loosening the clamp bolt and twisting the derailleur body.

4. Adjust the cable tension: The front derailleur cable should be tight enough to allow smooth and precise shifting, but not so tight that it causes chain rub or limit screw interference. Use the barrel adjuster on the shifter or the derailleur to find the right tension.

5. Check the limit screws: The front derailleur limit screws control the movement range of the derailleur. The low limit screw (L) prevents the chain from falling off the smallest ring, while the high limit screw (H) prevents the chain from falling off the largest ring. Adjust these screws using a screwdriver to ensure proper alignment.

2. Chain Drop

Another frustrating chainline problem is chain drop. This occurs when the chain falls off the front or rear sprocket while you’re shifting or riding. Not only does it result in a loss of power, but it can also damage the chain and pose a safety risk. Here’s how you can prevent chain drop:

1. Maintain your chain: Regularly clean, lube, and inspect your chain. Make sure it’s free of rust, dirt, or kinks. Additionally, ensure that your chain is the correct length and tension for your drivetrain.

2. Check your chainrings: Clean and inspect your chainrings regularly. They should be free of wear, damage, or bent teeth. Ensure that they’re compatible with your drivetrain and have the correct size and shape.

3. Inspect your sprockets: Like your chainrings, your sprockets should be clean, straight, and free of wear, damage, or bent teeth. They should also be compatible with your drivetrain and have the correct size and shape.

4. Maintain your derailleurs: Keep your derailleurs clean, aligned, and properly adjusted. Ensure they’re compatible with your drivetrain and have the correct position, height, angle, cable tension, and limit screws.

5. Check your shifters: Make sure your shifters are clean, functional, and calibrated properly. They should be compatible with your drivetrain and have the correct cable routing, indexing, and barrel adjustment.

3. Chain Suck

Chain suck is another common chainline problem that you’ll want to avoid. This occurs when the chain sticks to the bottom of the front chainring and gets pulled up into the frame. It can create noise, friction, and damage to both the chain and the frame. Here’s how to prevent chain suck:

1. Keep your chain clean: Regularly clean your chain with a degreaser and a brush or a chain cleaner tool. Make sure it’s free of dirt, rust, or any other debris that can cause it to stick.

2. Lubricate your chain: After cleaning, lube your chain with a suitable lubricant for your riding conditions. This will ensure smooth movement and reduce the chances of chain suck.

3. Maintain your chainrings: Clean your chainrings regularly with a degreaser and a rag or a toothbrush. Check for wear, damage, or bent teeth, and replace them if necessary.

4. Poor Shifting

Last but not least, poor shifting can ruin your cycling experience. This occurs when the chain doesn’t move smoothly or accurately between different gears, resulting in noise, hesitation, skipping, or jumping of the chain. Here’s how you can improve shifting performance:

1. Front derailleur adjustment: Refer to the earlier section on chain rub for tips on adjusting your front derailleur position, height, angle, cable tension, and limit screws.

2. Rear derailleur adjustment: The rear derailleur should be parallel to the rear sprockets and aligned with the smallest sprocket. Aim for a gap of about 6-8 mm between the upper pulley wheel and the smallest sprocket. Also, make sure the rear derailleur hanger is straight and perpendicular to the wheel axle.

3. Fine-tune the cable tension: The rear derailleur cable should be tight enough for smooth and precise shifting, but not so tight that it causes skipping or limit screw interference. Use the barrel adjuster on the shifter or the derailleur to find the optimal tension.

4. Check the limit screws: Similar to the front derailleur, the rear derailleur limit screws (low and high) control the movement range of the derailleur. Adjust them using a screwdriver to ensure proper shifting performance.

Conclusion

In summary, the bike chainline is an important concept for cyclists who want to optimize their drivetrain performance and avoid unnecessary wear and tear.

You can measure both the front and rear chainline separately by using a simple ruler or a digital caliper. If there is some wrong, you can also adjust the bike chainline by changing the position of your front or rear sprockets relative to the centerline of the bike frame. There are different methods for adjusting the chainline depending on the type and number of gears on your bike.

I hope this article helped you understand what a bike chainline is and how to measure and adjust it. If you have any questions or comments, feel free to leave them below. Happy cycling!

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AUTHOR

Randy Joycelyn

Randy is the founder and editor of Cycling Soigneur. He has been passionate about cycling since he was a kid. He has been riding bikes for over 10 years. Cycling has just become a part of life.

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