The Shimano CN-HG71 [paid link] chain is widely favored for its robustness and consistent performance across various drivetrain systems. Correct chain length is fundamental for ensuring optimal shifting performance, drivetrain longevity, and overall bike efficiency. In this guide, we will walk through the specific procedures for determining, adjusting, and verifying the ideal chain length for the Shimano CN-HG71 [paid link]. Proper chain length adjustment will prevent unnecessary wear on drivetrain components and ensure smooth and precise gear transitions.
Understanding the Importance of Correct Chain Length
Chain length directly affects drivetrain performance. A chain that is too short risks damaging the rear derailleur or limiting gear range, while a chain that is too long compromises shifting precision and increases the chance of chain drops. The CN-HG71 [paid link], with its Hyperglide design, demands precise sizing to leverage its engineered shift ramps and tooth profiles for smooth operation.
Achieving the correct length requires more than just guessing or reusing the old chain’s dimensions. Every bike has unique gear ratios and rear derailleur setups that influence the optimal chain size. Accurate measurement ensures the CN-HG71 operates efficiently within the bike’s geometry and drivetrain configuration.
Tools Required
- Chain tool (dedicated for 7/8-speed chains)
- Chain wear indicator
- Shimano-specific chain pin or quick link
- Chain checker for pre-installation inspection
- Gloves for cleaner handling
- Ruler or measuring tape (optional for verification)
Preparation Before Adjusting the Chain
Before starting, inspect the CN-HG71 to confirm it’s a genuine product. Check the chainrings and cassette for wear using a wear indicator tool. Installing a new chain on worn sprockets can result in poor performance and rapid chain wear. If the drivetrain components are excessively worn, replacement is advised before proceeding with the chain installation.
Ensure the rear derailleur, specifically the derailleur hanger, is straight and the derailleur pulleys are in good condition. A misaligned derailleur will distort the chain length evaluation and can cause skipping and inconsistent shifting.
Measuring the Correct Chain Length
For the Shimano CN-HG71, the most reliable method for determining chain length is the Big Chainring to Big Cog Method, often called the “Big-Big” method. Here’s how:
- Bypass the Rear Derailleur: Wrap the chain around the largest chainring at the front and the largest cog at the back without passing it through the rear derailleur.
- Align the Chain Ends: Pull the chain tight so that both ends meet without slack.
- Add Extra Links: Add two full links (one inner and one outer plate) to this length. This ensures the derailleur will have enough tension even in cross-chained situations.
Another method, suitable for bikes with suspension or specific derailleur types, is to measure with the derailleur included to simulate real-world conditions.
Important Consideration: Always ensure that the chain has a correct “quick link” or “connecting pin” if using Shimano’s provided methods. For CN-HG71, using Shimano’s reinforced chain pin is recommended for long-term durability.
Chain Installation Steps
Once the ideal length is determined:
- Remove Excess Links: Using a chain tool, remove the surplus links carefully. Avoid damaging adjacent plates.
- Install the Chain: Route the chain properly through the rear derailleur’s jockey wheels, ensuring it follows the correct path through the derailleur cage.
- Connect the Chain: Use the Shimano connecting pin, pressing it in firmly with a chain tool until it sits flush. Break off the guide pin once installed. Alternatively, if using a quick link, ensure it is properly engaged and locked.
After installation, manually rotate the crank and shift through all the gears to ensure there is no binding, skipping, or excessive slack. The derailleur cage should show appropriate tension in all gear combinations.
Common Mistakes in CN-HG71 Chain Length Adjustment
Mistakes in measuring and setting chain length can compromise drivetrain functionality. Here are typical errors to avoid:
- Using the old chain as a template: Chains stretch over time; replicating the old chain’s length carries forward incorrect dimensions.
- Skipping tension check: Failing to check derailleur tension after installation can lead to chain slap or poor shifting.
- Misrouting through derailleur pulleys: Routing the chain incorrectly through the derailleur will affect performance and may damage the derailleur.
- Neglecting suspension sag: For full-suspension bikes, not accounting for chain growth due to suspension movement can result in a chain that is too tight at full compression.
Verification and Testing
After installation, it’s essential to test the system thoroughly. Shift through all gears while the bike is on a workstand or while riding. The chain should move smoothly without hesitation or noise. Watch the rear derailleur cage: it should not be overly stretched in large cog combinations or excessively relaxed in small cog setups.
A correctly sized CN-HG71 chain will allow full gear range use without the derailleur being over-extended or the chain sagging in small-small combinations. Pay close attention to cross-chaining situations (big chainring to big cog, small chainring to small cog), as these will expose incorrect chain lengths.
Maintaining Proper Chain Length Over Time
Chains wear and stretch over time, which can lead to length inconsistencies. Regularly check the chain with a wear indicator tool. Replacing the chain before it reaches 0.75% wear prolongs the life of the cassette and chainrings, maintaining drivetrain efficiency.
Sticking to a maintenance routine that includes cleaning and proper lubrication will help the Shimano CN-HG71 maintain its original performance characteristics and ensure the chain stays at an optimal operational length.
Conclusion
Achieving the correct chain length for your Shimano CN-HG71 chain is crucial for drivetrain longevity and precise shifting performance. By following the measurement and installation procedures carefully, you ensure a smooth, efficient ride with minimized risk of mechanical failures. Regular maintenance and early detection of wear will extend the life of both your chain and drivetrain, keeping your bike running at peak performance.