Nothing ruins a ride faster than a skipping or grinding drivetrain. A properly tuned rear derailleur keeps your shifts crisp and your chain where it belongs. This tutorial explains how to adjust the limit screws, set cable tension and dial in the B‑screw on a mechanical (cable‑actuated) rear derailleur. We focus on road bikes because most drop‑bar bicycles still use cable‑actuated derailleurs, and the tighter cassette spacing and double chainrings on road drivetrains mean you must be meticulous about limit‑screw alignment and indexing. The basic principles are the same on mountain bikes, but electronic shifting systems use different adjustment procedures and are not covered here.

A rear derailleur is a spring‑loaded arm that moves a pair of pulleys across the cassette to select each gear. Two small limit screws, often marked H for high and L for low, restrict this lateral travel and keep the chain from overshooting the cassette at either end. A cable anchor bolt clamps the shift cable to the derailleur and a barrel adjuster fine‑tunes cable tension. The B‑screw sets the gap between the upper guide pulley and the cassette teeth.Understanding what each adjustment does makes the tuning process intuitive.

1. Shift into the smallest rear cog and the big chainring. This puts the derailleur at its outer limit. If possible, place your bike in a work stand so you can pedal and shift while adjusting.
2. Release cable tension. Using a 5 mm hex key, loosen the cable anchor bolt so the cable is free.Wind the barrel adjuster (at the derailleur or shifter) all the way in and then back it out a turn or two to give yourself some adjustment range later.
3. Check the hanger and drivetrain. A bent hanger or worn chain will make tuning impossible. If shifting is erratic even after following these steps, you may need to straighten the hanger or service the derailleur.

The H‑limit screw stops the derailleur moving too far outward, which would push the chain past the smallest cog. Turn the screw until the guide pulley aligns exactly with the smallest cog, then back it off slightly so the pulley sits just a hair (~1 mm) outboard. Pedal by hand to ensure the chain stays on the cog. If it rubs the next cog, back the screw out a fraction; if the chain wants to jump off the cassette, tighten it.

Pull the shift cable taut and re‑clamp it under the anchor bolt, removing any slack. Click the shifter one gear to move into the second smallest cog. If the chain doesn’t climb cleanly, turn the barrel adjuster anti‑clockwise (adding tension) until the shift happens crisply, then go another quarter turn. Shift back to the smallest cog and test again. Repeat this process, shifting up and down, until each click moves the chain one cog. Remember to pedal lightly while shifting—keeping some load on the chain but easing off pressure helps the derailleur move smoothly.

The B‑screw controls the guide pulley’s distance from the cassette.With the chain in the largest cog, turn the B‑screw until the top pulley sits close to the cassette teeth without touching.A gap of 5–6 mm works well for most drivetrains. If you install a cassette with a larger largest cog, you’ll often need to back theB‑screw out to clear the bigger sprocket.

Run through all the gears, shifting one click at a time. If the chain skips on certain cogs or hesitates to shift, fine‑tune the barrel adjuster in quarter‑turn increments. Persistent issues in the smallest or largest cogs usually indicate the limit screws need minor tweaks. If shifting feels perfect on the small cogs but not the big ones, a bent derailleur hanger is often the culprit. A simple hanger alignment tool can straighten it, or your local bike shop can help.

This tutorial is for riders who want to keep their cable‑actuated road bike shifting smoothly without a trip to the mechanic. Whether you commute, ride for fitness, race or simply enjoy long weekend rides, a well‑adjusted rear derailleur makes every shift feel effortless.These skills are especially handy if you swap wheels or cassettes frequently or want to fine‑tune your road drivetrain at home.