Rear Gear Alignment Systems: Damage and Correction
The Function of a Frame's Derailleur Mounting Point
This element, typically a replaceable part, serves as the interface between the bicycle frame and the rear gear-changing mechanism. Its primary purpose is to provide accurate and consistent positioning for shifting performance. It also protects the frame from damage in the event of impact.
Common Causes of Misalignment or Damage
- Impact: Direct strikes during crashes or from trail debris.
- Improper Handling: Rough handling during transport or storage.
- Over-Tightening: Excessive force when installing or removing the rear gear mechanism.
- Wear and Tear: Gradual deformation due to repeated stress over time.
Recognizing Misalignment
Indicators can include:
- Poor shifting performance, especially hesitation or skipping gears.
- Excessive noise from the drivetrain.
- Visible bends or kinks in the metal.
- Difficulty achieving proper gear adjustment.
Tools and Techniques for Assessing Alignment
Derailleur Alignment Gauge
This specialized tool is designed to measure the parallelism of the rear gear mounting surface relative to the rear wheel. It typically attaches to the rear gear mounting point and allows for precise measurements at various points around the wheel's circumference.
Visual Inspection
Careful observation can sometimes reveal obvious distortions. However, minor misalignments may be difficult to detect with the naked eye.
Corrective Measures
Realignment Procedures
Using a alignment gauge, gentle and controlled bending can correct minor misalignments. Extreme caution should be exercised to avoid cracking or breaking the material. It's often preferable to make small adjustments incrementally and recheck the alignment frequently.
Replacement
If significantly damaged or fatigued, replacement is generally recommended. Ensure a compatible replacement is obtained, matching the frame and gear system specifications.
Post-Correction Adjustments
After realignment or replacement, the rear gear system will likely require readjustment. This includes setting the limit screws, cable tension, and B-tension to ensure optimal shifting performance.
Material Considerations
The material composition of the mounting point (typically aluminum alloys) significantly impacts its durability and susceptibility to damage. Some alloys are more prone to bending than others, while others may be more brittle and prone to cracking.