The chain line on a mountain bike is the straight line between the center of the bottom bracket and the center of the rear cassette. It is important to have the correct chain line in order to ensure that the chain runs smoothly and does not rub against the frame or other components. Measuring the chain line is a relatively simple process, and it can be done with a few basic tools.
To measure the chain line, you will need a ruler or measuring tape and a straight edge. Place the straight edge against the teeth of the chainring and measure the distance from the straight edge to the center of the bottom bracket. Next, place the straight edge against the teeth of the largest cog on the cassette and measure the distance from the straight edge to the center of the bottom bracket. The difference between these two measurements is the chain line. The ideal chain line for a mountain bike is 47.5mm. However, it is acceptable to have a chain line that is within 1-2mm of this ideal.
Determining Frame Alignment
Measuring chain line begins with determining the frame’s alignment. If the frame is misaligned, even the most precise chain line adjustments will be futile. Here’s a step-by-step guide to ensuring proper frame alignment:
- Check the rear wheel alignment: Place the bike on a truing stand or flat surface. Spin the rear wheel and observe it from the rear. If the wheel wobbles from side to side, it indicates a misaligned frame.
- Use a string: Tie a string tight around the head tube and rear dropout on one side of the bike. Measure the distance from the string to the rim on both sides of the wheel. If the measurements are different, the frame is out of alignment.
- Use a laser chain line tool: These tools project a laser beam parallel to the frame. Position the tool on the head tube and align the laser with the rear dropout. Any deviation from the laser line indicates frame misalignment.
| Frame Alignment Check | Method |
|---|---|
| Rear Wheel Alignment | Truning stand/ Flat surface |
| String Method | String and measurements |
| Laser Chain Line Tool | Laser projection |
Identifying Chainrings and Crankarms
Crankarms
Crankarms are the arms that connect the pedals to the bottom bracket and rotate together. They are typically made of aluminum or carbon fiber and come in various lengths. The length of the crank arm is measured in millimeters (mm) from the center of the bottom bracket to the center of the pedal spindle.
The chainrings are attached to the crank arms and are responsible for transferring power from the pedals to the chain. They are typically made of aluminum or steel and come in various sizes. The size of the chainring is measured in teeth, which determine the gear ratio of the bicycle.
To measure the chain line, you will need to use a chain line gauge. This tool is a simple device that consists of a straight edge and a series of holes. The holes are spaced at different distances from the center of the tool, which allows you to measure the distance between the chainrings and the crank arms.
To measure the chain line, place the straight edge of the chain line gauge against the inside edge of the largest chainring. Then, use the holes in the gauge to find the closest hole that aligns with the center of the crank arm. The distance between the hole and the straight edge of the gauge is the chain line.
Chainrings
Chainrings are typically mounted on the crank arms using bolts or spider arms. The chainrings come in a variety of sizes, which affect the gear ratio of the bicycle. The larger the chainring, the easier it is to pedal, but the slower the bike will go. Conversely, the smaller the chainring, the harder it is to pedal, but the faster the bike will go.
The number of teeth on the chainring is also important. The more teeth on the chainring, the more gears the bicycle will have. A bicycle with a triple chainring setup will have three different chainrings, each with a different number of teeth. This allows the rider to choose the gear that is best suited for the terrain and riding conditions.
| Number of Teeth | Gear Ratio |
|—|—|
| 10 | 1:1 |
| 11 | 1.1:1 |
| 12 | 1.2:1 |
| 13 | 1.3:1 |
| 14 | 1.4:1 |
| 15 | 1.5:1 |
| 16 | 1.6:1 |
| 17 | 1.7:1 |
| 18 | 1.8:1 |
| 19 | 1.9:1 |
| 20 | 2:1 |
Using a Chain Line Gauge
To measure chain line using a chain line gauge, follow these steps:
- Place the chain line gauge on the rear hub’s axle.
- Slide the gauge until the indicator pointer aligns with the center of the small chainring.
- Read the measurement on the gauge where it aligns with the edge of the indicator pointer. This measurement indicates the chain line offset from the center of the axle.
Measuring Chain Line Offset
The chain line offset, or the distance between the chain line and the center of the hub axle, is crucial for proper drivetrain performance. An offset of 0mm means that the chain line is perfectly aligned with the center of the hub axle. Positive offsets indicate that the chain line is shifted to the non-drive side, while negative offsets indicate a shift to the drive side.
The optimal chain line offset can vary slightly depending on the specific drivetrain components and frame design. However, as a general rule, most single-chainring drivetrains prefer a chain line offset of 0mm to 3mm. This range allows for smooth shifting and minimizes drivetrain wear.
The table below provides a detailed breakdown of chain line offsets for different types of drivetrains:
| Drivetrain Type | Optimal Chain Line Offset |
|---|---|
| Single-chainring | 0mm to 3mm |
| Double-chainring | 0mm to 5mm |
| Triple-chainring | 0mm to 7mm |
Measuring with a Tape Measure
Using a tape measure to measure your mountain bike’s chainline is a simple and straightforward process. Here are the steps:
- Place the bike upside down on a flat surface.
- Locate the centre of the bottom bracket shell.
- Mark this point with a piece of tape or a marker.
- Measure the distance from the centre of the bottom bracket shell to the chainring. This is your chainline measurement.
Tip: When measuring with a tape measure, be sure to use a straight edge to ensure accuracy.
Checking the Chainline
Once you have measured the chainline, you can check it against the manufacturer’s specifications. Most mountain bikes have a chainline of 47.5mm or 50mm. If your measurement is significantly off from these specifications, it may indicate a problem with your drivetrain.
Troubleshooting
If you find that your chainline is off, there are a few things you can check:
- Make sure that the chainring is properly aligned.
- Check the bottom bracket for any damage or play.
- Inspect the chain for any damaged or stretched links.
If you are unable to resolve the issue on your own, you should take your bike to a qualified bike mechanic for further diagnosis and repair.
Assessing Chainring Offset
Chainring offset refers to the lateral displacement of the chainring from the bike’s center line. It plays a crucial role in achieving optimal chainline and preventing premature wear on components.
To measure chainring offset, you’ll need a ruler or measuring tape and a flat surface. Follow these steps:
- Place the ruler or measuring tape on a flat surface parallel to the bike’s center line.
- Position the chainring over the ruler, aligning the inner or outer edge with the zero point.
- Measure the distance from the zero point to the center of the chainring.
- Repeat the measurement for both the inner and outer edges of the chainring.
- To accurately determine the chainring offset, subtract the smaller measurement from the larger measurement. The resulting value is the chainring offset, which should be noted in millimeters (mm).
If the measurements are not equal, the chainring is not centered and has a positive or negative offset. A positive offset indicates that the outer edge of the chainring is further away from the center line than the inner edge, and a negative offset indicates the opposite.
| Measurement | Value (mm) |
|---|---|
| Inner edge | 32 |
| Outer edge | 37 |
| Chainring offset | 5 |
Using a Laser Level
To use a laser level to measure chain line, you will need a laser level, a ruler, and a marker.
1. Place the laser level on a flat surface near the bike.
2. Turn on the laser level.
3. Position the ruler so that the zero mark is aligned with the center of the chainrings.
4. Hold the ruler vertical and align it with the laser beam.
5. Mark the point on the ruler where the laser beam intersects it.
6. Repeat steps 3-5 for the rear sprocket. The distance between the two marks on the ruler is the chain line.
Here is a table summarizing the steps for using a laser level to measure chain line:
| Step | Description |
|---|---|
| 1 | Place the laser level on a flat surface near the bike. |
| 2 | Turn on the laser level. |
| 3 | Position the ruler so that the zero mark is aligned with the center of the chainrings. |
| 4 | Hold the ruler vertical and align it with the laser beam. |
| 5 | Mark the point on the ruler where the laser beam intersects it. |
| 6 | Repeat steps 3-5 for the rear sprocket. The distance between the two marks on the ruler is the chain line. |
Measuring from the Frame
This method is the most accurate but requires a bit more work. You’ll need a straight edge (ideally a meter stick), a ruler, and a small square. Some chain-checking tools may also come with an integrated ruler, if available, you can use this instead.
Step 1: Set the bike on the stand
Place your bike on a stand to keep it stable. Ensure the bike is level and the chain is on the smallest chainring and largest cog. This setup creates the maximum chainline offset.
Step 2: Align the square to the chainstay
Place the small square against the outside of the chainstay, perpendicular to the ground. Use the ruler to measure the distance from the center of the square to the center of the bike’s spindle where the crank arm attaches.
Step 3: Estimate the chainline
Take this measurement and divide it by two. This value represents the chainline offset. Add this offset to the frame’s recommended chainline to get the actual chainline measurement.
Example
If the measurement from the square to the spindle is 50.4 mm and the frame recommends a chainline of 49 mm, the actual chainline would be 49 mm + (50.4 mm / 2) = 74.9 mm.
| Measurement from square to spindle | Frame’s recommended chainline | Actual chainline |
|---|---|---|
| 50.4 mm | 49 mm | 74.9 mm |
Calculating the Ideal Chain Line
Calculating the ideal chain line is crucial to ensure smooth and efficient shifting. Here’s how to determine the correct chain line for your mountain bike:
Step 8: Confirm the Cassette and Chainring Alignment
Once the rear wheel is aligned, it’s essential to confirm the alignment of the cassette and chainring. Use a chain line measuring tool or a straightedge to measure the distance from the center of the cassette to the center of the chainring. The ideal distance, known as the “chain line offset,” varies depending on the specific components used.
Refer to the manufacturer’s specifications or use a chain line compatibility chart to determine the desired chain line offset. Typically, the offset should be around 1-2mm for narrow-wide chainrings and 4-6mm for standard chainrings. By ensuring proper cassette and chainring alignment, you can optimize shifting performance and minimize chain wear and noise.
To fine-tune the chain line further, consider using chainring spacers. These spacers can be added or removed to adjust the chain line by small increments, allowing for precise alignment.
| Chainring Type | Ideal Chain Line Offset |
|---|---|
| Narrow-Wide Chainrings | 1-2mm |
| Standard Chainrings | 4-6mm |
Adjusting the Chain Line
Adjusting the chain line is crucial for optimal performance of your mountain bike. It ensures that the chain runs smoothly through the gears without rubbing against the cassette or chainrings. Here’s how to adjust the chain line:
1. Measure the Chain Line
Use a chain line gauge or ruler to measure the distance between the center of the rear axle and the center of the smallest chainring. The optimal chain line for most MTBs is typically 47.5mm to 49.5mm.
2. Check the Derailleur Position
Start by checking the position of the rear derailleur. It should be aligned parallel to the cassette. If it’s not, adjust the cable tension or the high/low limit screws until it aligns.
3. Adjust the Axle Position
If the derailleur is aligned but the chain line is still off, you may need to adjust the axle position. Loosen the axle nuts and slide the axle forward or backward to achieve the correct chain line.
4. Check Spoke Dish
Spoke dish refers to the offset of the rear wheel spokes. Ensure that the spokes are evenly tensioned and that the wheel is centered in the frame. Uneven spoke tension or a misaligned wheel can affect the chain line.
5. Use Spacers
If fine-tuning the axle position doesn’t yield satisfactory results, consider using spacers. Place spacers between the hub and the frame to adjust the chain line. Ensure the spacers are compatible with your hub and frame.
6. Check the Bottom Bracket
In some cases, a worn or misaligned bottom bracket can affect the chain line. Check the bottom bracket bearings and ensure they’re properly tightened and adjusted.
7. Inspect the Chainstays
Inspect the chainstays for any bends or damage. Deformed chainstays can alter the rear axle position, which in turn affects the chain line.
8. Check the Cassette
Examine the cassette for any bent or damaged teeth. A misaligned or worn cassette can cause the chain to shift poorly and affect the chain line.
9. Install a Chain Line Tool
For precision adjustments, consider installing a chain line tool. This tool mounts on the rear axle and provides a visual reference for aligning the chain line with the chainrings and cassette. It simplifies the process and ensures optimal chain line.
1. Measure the Right Distance
The distance between the center of the chainring and the center of the cassette should be measured. This is not the same as the distance between the outer edge of the chainring and the outer edge of the cassette.
2. Use a Chain Measuring Tool
The most accurate way to measure chain line is to use a chain measuring tool. These tools are designed to measure the distance between the center of the chainring and the center of the cassette.
3. Check the Tension of the Chain
The tension of the chain can affect the chain line. If the chain is too tight, it can cause the chain to pull the cassette in towards the frame. If the chain is too loose, it can cause the cassette to move away from the frame.
4. Use a Straight Edge
If you do not have a chain measuring tool, you can use a straight edge to measure the chain line. Place the straight edge on the back of the chainring and extend it to the back of the cassette. The distance between the straight edge and the center of the cassette is the chain line.
5. Check the Alignment of the Chain
The alignment of the chain can also affect the chain line. If the chain is not aligned properly, it can cause the cassette to move in either direction.
6. Make Sure the Drivetrain is Clean
A dirty drivetrain can cause the chain to become stiff and difficult to move. This can make it difficult to get an accurate chain line measurement.
7. Use a Torque Wrench
When tightening the chainring bolts, be sure to use a torque wrench. Over-tightening the chainring bolts can cause the chainring to bend, which can affect the chain line.
8. Check the Chainring and Cassette
The chainring and cassette should be inspected for any signs of damage or wear. A damaged or worn chainring or cassette can cause the chain line to be off.
9. Use a New Chain
A new chain is more likely to be stretched evenly than an old chain. This can help to ensure an accurate chain line measurement.
10. Consider the Following Factors
In addition to the tips listed above, there are a few other factors that can affect the chain line of your bike. These factors include:
| Factors | Chain Line |
|---|---|
| Frame design | Some frames are designed with a specific chain line in mind. Changing the chain line on these frames can affect the performance of the bike. |
| Rear derailleur | The rear derailleur can affect the chain line by moving the cassette in or out. |
| Bottom bracket | The bottom bracket can affect the chain line by changing the distance between the chainring and the cassette. |
It is important to consider all of these factors when measuring the chain line of your bike.
How to Measure MTB Chain Line
The chain line on an MTB is the distance between the center of the bike’s frame and the center of the chain. It is important to measure the chain line because it will affect the performance of the bike’s drivetrain. If the chain line is too far out of alignment, the chain will be more likely to skip or break, and the drivetrain will be less efficient. To measure the chain line, you will need a chain line gauge, which is a tool that can be purchased from most bike shops.
To use a chain line gauge, first remove the rear wheel from the bike. Then, place the gauge on the bike frame, with the center of the gauge aligned with the center of the bottom bracket. The gauge will have two arms, one that is longer than the other. The longer arm should be extended so that it is pointing towards the rear of the bike, and the shorter arm should be rotated so that it is pointing towards the front of the bike.
Once the gauge is in place, adjust the shorter arm so that it is touching the chain. The center of the gauge will now be lined up with the chain line. You can then use a ruler to measure the distance between the center of the gauge and the center of the bike frame. This measurement is the chain line.
People Also Ask About How to Measure MTB Chain Line
What is the ideal chain line for an MTB?
The ideal chain line for an MTB is between 47.5mm and 50mm. This range provides the best balance of chain efficiency and durability.
What are the consequences of having a chain line that is too far out of alignment?
If the chain line is too far out of alignment, the chain will be more likely to skip or break, and the drivetrain will be less efficient. In extreme cases, a chain line that is too far out of alignment can cause damage to the bike’s frame or components.
How often should I check my chain line?
It is a good idea to check your chain line every time you change your chain or cassette. You should also check it if you experience any problems with your drivetrain, such as skipping or breaking chains.
