How a Derailleur Works & Tips for Replacing It
The derailleur is a crucial component of your bicycle's drivetrain, responsible for shifting the chain between different gears on the cassette (rear gears) or chainrings (front gears). This system allows you to adjust your pedaling effort and maintain an optimal cadence depending on the terrain.
Rear Derailleur
How a Derailleur Works
Changing Gears Efficiently: Bicycles equipped with derailleurs have multiple gears, allowing you to adjust your mechanical advantage. Shifting up moves the chain to a larger chainring or smaller rear cog, making pedaling harder but increasing speed. Shifting down moves the chain to a smaller chainring or larger rear cog, making pedaling easier and ideal for climbing hills.
Adapting to Terrain
Flat Roads / Downhills → Use higher gears to increase speed and efficiency.
Uphill / Rough Terrain → Use lower gears to make pedaling easier and reduce strain on your legs.
Smooth & Precise Shifting: Gear changes are controlled via shifters on the handlebars, which pull or release cable tension to move the derailleur. Indexed shifting (found on modern bikes) ensures the derailleur "clicks" into precise positions for smoother and more accurate gear changes.
Front vs. Rear Derailleur
Front Derailleur moves the chain between multiple front chainrings.
Rear Derailleur controls movement across the cassette, handling more frequent shifts for precise gearing adjustments.
Common Derailleur Issues
Skipping gears? Your derailleur may need cable tension adjustment.
Slow shifting? Check for dirty cables, worn-out jockey wheels, or bent derailleur hangers.
Chain rubbing? Adjust the limit screws to ensure the derailleur isn’t moving too far inward or outward.
Watch this: https://www.youtube.com/watch?v=GUryLeKWtxY
Replacing a Derailleur: Step-by-Step
Tools You'll Need
Allen wrenches (typically 5mm or 6mm)
Phillips screwdriver (for limit screws)
Chain breaker (if replacing a damaged chain)
Derailleur hanger alignment tool (optional but helpful)
Lubricant for smooth shifting
Phillips screwdriver (for limit screws)
Chain breaker (if replacing a damaged chain)
Derailleur hanger alignment tool (optional but helpful)
Lubricant for smooth shifting
Step 1: Remove the Old Derailleur
Shift the bike into the smallest chainring and smallest rear cog.
Loosen the derailleur cable bolt to release cable tension.
Use an Allen wrench to unscrew the derailleur from the derailleur hanger.
Remove the chain from the jockey wheels and detach the derailleur completely.
Loosen the derailleur cable bolt to release cable tension.
Use an Allen wrench to unscrew the derailleur from the derailleur hanger.
Remove the chain from the jockey wheels and detach the derailleur completely.
Step 2: Install the New Derailleur
Attach the new derailleur to the hanger and tighten the mounting bolt securely.
Reconnect the chain (make sure it's properly sized).
Thread the derailleur cable through the cable pinch bolt and tighten it slightly.
Reconnect the chain (make sure it's properly sized).
Thread the derailleur cable through the cable pinch bolt and tighten it slightly.
Step 3: Adjust the Derailleur for Smooth Shifting
Limit Screws (H & L) Adjustment:
The H (high) screw sets the smallest cog limit, preventing the chain from overshifting off the cassette.
The L (low) screw sets the largest cog limit, ensuring the chain doesn’t jump into the spokes.
B-Tension Screw Adjustment:
Adjusts the distance between the derailleur and cassette for better chain engagement.
Turn clockwise to move the derailleur away from the cassette and counterclockwise to bring it closer.
Cable Tension Adjustment:
Use the barrel adjuster on the shifter or derailleur to fine-tune shifting performance.
If shifting is slow moving to a larger cog, increase tension.
If shifting is slow-moving to a smaller cog, decrease tension.
Replacing a Derailleur Hanger & Why It’s Important
The derailleur hanger is a small but critical component that attaches the derailleur to the bike frame. It is designed to bend or break during a crash to protect your frame.
How to Find the Correct Derailleur Hanger
Check your bike’s manual for manufacturer specifications.
Look for markings on your current hanger (some have model numbers).
Visit the manufacturer’s website for compatibility charts.
Bring your old hanger to a local bike shop for a match.
Use online databases that allow searching by bike brand/model.
Measure dimensions (hole spacing, diameter, overall length) if unsure.
Look for markings on your current hanger (some have model numbers).
Visit the manufacturer’s website for compatibility charts.
Bring your old hanger to a local bike shop for a match.
Use online databases that allow searching by bike brand/model.
Measure dimensions (hole spacing, diameter, overall length) if unsure.
Replacing a Hanger: Quick Steps
Remove the rear wheel for easier access.
Unscrew and remove the damaged hanger.
Align and attach the new hanger, ensuring it's straight.
Tighten the bolts securely (but do not overtighten).
Check derailleur alignment and make fine adjustments as needed.
Unscrew and remove the damaged hanger.
Align and attach the new hanger, ensuring it's straight.
Tighten the bolts securely (but do not overtighten).
Check derailleur alignment and make fine adjustments as needed.
Final Tips for Smooth Shifting & Longevity
Keep your drivetrain clean – Dirt buildup can cause shifting issues.
Lubricate moving parts to reduce friction and wear.
Check derailleur alignment regularly – A bent hanger can cause misalignment.
Replace cables & housing periodically to ensure crisp shifting.
Use the correct chain length – A chain that's too long or too short affects performance.
Lubricate moving parts to reduce friction and wear.
Check derailleur alignment regularly – A bent hanger can cause misalignment.
Replace cables & housing periodically to ensure crisp shifting.
Use the correct chain length – A chain that's too long or too short affects performance.
By understanding how derailleurs work and learning proper maintenance, you can ensure smooth, precise shifting and get the most out of your bike's performance!
Front Derailleur
