Workshop: How to set up the gears on your bike

Find stop screws (Bikeradar)

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A silent and smooth-running transmission can make all the difference to your ride. Follow our 16-step guide carefully and you’ll get it right, every time. 

This guide is aimed mainly at mountain bikers, but many of the same principles apply to road bikes. Check out our Shifting Problems workshop for details of how to index Campagnolo, Shimano and SRAM road gearing.

Tools

• Phillips screwdriver
• Pliers or third hand tool
• 3mm & 5mm Allen keys
• Chain tool
• Chain lubricant

1 Find stop screws

With the front mech in place and the chain removed, the first step is to locate the stop screws. These control the range of motion, and are marked H (high) and L (low). They’re adjusted with a Phillips screwdriver.

On a top-swing front mech, the L screw is the inner one — it controls the limit of the mech’s inward motion. The high screw is the outermost one, that limits the mech’s outward motion. On a bottom-swing mech, this is reversed.

2 Set front screws

Set the L screw so that the front mech cage’s inner plate is roughly 4mm from the smallest chainring. Then, pushing the mech cage out by hand, set the H screw so that the outermost plate of the mech cage is 4mm from the outside of the big chainring.

3 Set rear screws

Similarly, roughly set the rear mech’s H and L screws. Turning the screws anti-clockwise allows the mech to move towards the spokes, and turning it clockwise moves it away from the spokes. The top jockey wheel of the mech should stop directly under the largest cassette sprocket (adjust the L screw to do this), and directly below the smallest cassette sprocket (adjust the H screw).

4 B-angle screw

Most rear mechs have a third screw — called the B-tension or B-angle screw — which adjusts the clearance between the top jockey wheel and cassette sprockets. Using a Phillips screwdriver, adjust it so that the distance is 5-6mm. This ensures that when you put the chain on it’ll be close enough for quick shifting, yet clear enough that the shifts are still clean.

5 Fit gear cables

Apply a light lube to the gear cable outers to help ensure the free running of the gear cable. Then thread a new, clean gear cable through the bar-mounted shifters and through the gear outers for both the front and rear mech.

6 Set front cable

With the front shifter set on the lowest gear position (normally marked ‘1’), run the gear cable through the anchor bolt of the front mech. Pull it taut using a pair of pliers at the same time as you tighten the anchor bolt. Push the gear shifter a few times to seat the cable properly, then loosen the anchor bolt, take up the slack and re-tighten.

7 Set rear cable

With a normal rear mech, set its shifter on the lowest gear position (usually marked ‘1’). For a Low Normal/Rapid Rise mech that springs to the smallest sprocket, set it to the highest gear position (usually marked ‘8’ or ‘9’). Thread the cable through the anchor bolt and hold the cable tight with pliers before securely fastening it. Push the shifter a few times to seat the cable. Then loosen the bolt, take up the slack and re-tighten.

8 Chain length

To get the correct chain length, bypass the rear mech and thread the new chain around the big chain ring and the biggest rear sprocket only. Bring the chain ends taut and together, and add three whole chain links. Remove any excess length of chain using a chain tool. This should give you the correct chain length for your gearing.

9 Thread the chain

Thread the new chain through the front mech cage, over the cassette sprockets, over the top jockey wheel, through the rear derailleur cage and around the lower jockey wheel correctly. Drop it off the big ring to rest on the bottom bracket shell and onto the smallest cassette sprocket, to give you enough free links to join the cage together easily.

10 Join the chain

For a Shimano chain, bring the links together and insert a Shimano joining pin. Press the pin into place with a chain tool and snap off the protruding guide pin with pliers. For SRAM chains, use the PowerLink to connect the chain by slotting each half of the link through each end of the chain, and then bringing them together to snap the two pin halves of the link together. Finally, pull the halves to securely seat the link.

11 Check the chain

With the chain in place, check the front and rear mech stops. The front mech plates should clear the chain by 2mm. If there’s any rubbing, fine-tune the H/L screws accordingly to move the mech plates, but make sure the chain won’t be dumped off by the small or large chainrings during a rapid or dynamic shift. The rear mech jockey wheels should be directly beneath the largest and smallest sprockets at their H and L limits.

12 Gear indexing

Once the stop screws and B-angle screws are correctly adjusted, the rear mech’s indexing can be sorted. This is done by changing the tension of the gear cable at the barrel adjuster, which is on both the shifter and rear mech for Shimano and at the shifter only for SRAM. Shift the chain to the largest chainring and shift the rear mech, from the smallest sprocket, by one click only. If the shift isn’t smooth, cable tension is too slack.

13 Remove slack

Turn the barrel adjuster all the way in — at the rear mech or shifter — and then make two turns anti-clockwise to allow for adjustments. Loosen the inner wire pinch bolt and gently pull through any cable slack using a third hand tool or a pair of pliers. Then tighten the pinch bolt.

14 Tension SOS

If the mech won’t shift one sprocket after removing the slack, change the shifter to the highest gear (smallest cog) position. Increase the cable tension by turning the barrel adjuster on the mech or shifter anti-clockwise by a quarter of a turn. Shift to the second smallest sprocket. Turn the pedals and increase cable tension by turning the barrel adjuster anti-clockwise until you hear rattling — this is the chain scraping against the next sprocket.

15 Removing the rattle

Once this rattle occurs, turn the barrel adjuster clockwise by a quarter-turn to release the cable tension, and then pedal again. Listen and look for signs of chain scraping and/or rattling, and continue to turn the barrel adjuster clockwise by quarter-turns until any rattling disappears.

16 Final check

Shift by one sprocket at  a time from the smallest cog to  the largest, listening and looking for signs of rattling that would indicate the inner cable tension is too tight. Turn the barrel adjuster clockwise by a quarter-turn at a time to eliminate any rattle. Shift the front mech to the smallest chainring and check the gears again. If there’s no rattling or chain rubbing, the gears are properly indexed. Simply lube the chain and you’re ready to ride.

Top tips

> If you want to set up your mechs with the chain in place, you can either split it or undo the mech’s cage split clamp using a screwdriver and slip the chain out. Rest it on the bottom bracket shell. At the rear, remove the jockey wheels using a 3mm Allen key and slip the chain out of the cage, before replacing the jockey wheels and reassembling the mech cage.

> If you’re still having problems after setting up your transmission, or if the chain is rubbing excessively on the front mech, the mech cage might be damaged or might not be parallel with the chainrings. To adjust the mech cage, undo the mech clamp on the seat tube and tweak it so that the cages line up, then retighten the clamp and attach the gear cable.

> Problems with bad rear shifts may be due to a bent gear hanger, so check and replace as necessary.

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