Poorly indexed gears can be one of the most frustrating things on a bike, but our step-by-step guide can show you how to adjust your bike gears to get them running smoothly.
Like your brakes, gears rely on correct adjustment and the smooth operation of cables to work well.
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Modern gears are indexed — that is to say, as you click the gear lever into a gear position on the handlebars, the front or rear derailleur puts the chain onto the corresponding cog or ring. It should do this effortlessly and without any fuss.
It should not go into a different gear position nor should it slip into another gear as you pedal along.
When the gears are working well you cannot shift gear past either the largest or the smallest cog or chainring.
Incorrect derailleur adjustment may not sound as dangerous as ineffective brakes, but having a derailleur slip into your spokes, having a chain come off the front chainring, or having your gears slip can all result in a trip to casualty!
Adjusting the rear derailleur
Put the gear lever into top gear, turn the pedals and allow the chain to go onto the smallest cog on the cassette. If there is a cable adjuster on the gear lever body, or the derailleur body, screw it almost all the way in (clockwise).
Undo the cable-securing bolt on the derailleur and move the cable out of the way.
Turn the pedals while using your other hand to manually push the rear derailleur in towards the rear wheel.
If the derailleur’s inner adjusting screw is correctly adjusted, the chain will only travel onto the largest cog and go no further.
If it goes beyond that cog and falls into the spokes, turn the derailleur adjusting screw in (clockwise) and repeat step three. If the chain does not sit comfortably on the biggest cog, unscrew the adjusting screw a little and try again.
Once you’re happy with that, allow the derailleur’s spring to push the derailleur outwards onto the smallest cog.
Again if the chain comes off, or does not sit properly on the smallest cog, turn the other adjusting screw to move the derailleur’s position.
When the derailleur’s travel goes comfortably between the high and low cogs on the cassette, refit the gear cable and do up the securing bolt.
Using the gear lever, go through all the gears several times. If the derailleur is slow to go into the lower gears, unscrew the cable adjuster on the derailleur body.
If it is slow to go into the higher gears, screw in the cable adjuster. Re-check that all the securing bolts are tight and go for a gentle test ride.
Adjusting the front derailleur
Put the gear lever into the lowest gear, and if there is a cable adjuster on the gear lever body, screw it almost all the way in. Undo the cable-securing bolt on the operating lever of the derailleur and move the cable out of the way.
Check that the front derailleur is parallel to the chainring, and there is a gap of around 2mm between the top of the largest chain wheel and the bottom of the outer plate of the front derailleur.
If not, loosen the fixing clamp and realign the derailleur.
With the chain on the biggest cog at the rear, adjust the ‘inner’ adjusting screw so that when the chain is on the smallest chainring it sits in the middle of the derailleur side plates.
Now with the chain on the smallest cog on the rear cassette, pedal the bike with one hand and pull the front derailleur so that the chain goes onto the largest chainring at the front, and is again in the middle of the derailleur plates.
You achieve this by screwing or unscrewing the ‘outer’ adjusting screw on the derailleur body.
Let the derailleur return to its position over the smallest chain ring. Refit the cable, and tighten the securing bolt.
With the bike held off the ground, and the chain now on the largest cog at the back, test the front derailleur by moving the chain between the smallest and next chainring using the gear lever.
Do this with the crank arm at 12 o’clock, 3 o’clock, 6 o’clock and 9 o’clock, so that any slight bend in the chainring becomes apparent. If the chain falls off the smaller chainring, adjust the ‘inner’ derailleur adjusting screw so that the derailleur does not go so far in.
When you’ve done this successfully, and with the gear lever back in ‘1’ or ‘low’ and the chain on the small chainring, loosen the cable securing bolt and take up the slack on the cable.
Put the chain onto the smallest cog on the rear cassette. If you have a three-ring crankset, repeat the procedure above, this time going from the middle chainring to the biggest chainring.
If the chain falls off the front of the chainring, adjust the ‘outer’ derailleur adjusting screw, so the derailleur does not move quite so far out.
If you find that the derailleur is slow changing up from small to big chainring, unscrew the cable adjuster on the gear lever body a little.
Just be sure that is does not then become slow changing down. Recheck that all the securing bolts are tight and go for a gentle test ride.