The ability to change gears quickly and smoothly can mean the difference between getting up that steep trail or being stuck walking your bike through the mud. If the gears on your mountain bike don't seem to be shifting with the same snap they used to, your shifter cables that lead from your handlebars to your derailleurs may have stretched. Getting these cables tight again only takes a light turn of a screw. The trick is to not tighten too much or you'll be left struggling to change your bike's gears.
Front Derailleur Adjustment
Mount your bike into the work stand. Position the bike so you can turn the pedals freely.
Use the shifter on the left side of the handlebars to shift onto the smallest chain ring of your front gears. Use the shifter on the right side of your handlebars to move your chain onto the largest cog of your rear cassette.
Locate the high and low gear adjustment screws. These are two screws side by side that are located near the clamp of your front derailleur. The low gear screw is the one closest to the bike frame if the screws are horizontal. If the screws are vertical, the low gear screw is the top one. The screws on most modern bikes are marked with "H" and "L" for high and low.
Turn the screw clockwise to tighten your cable until the cage of the inside of the front derailleur cage is 2 millimeters from the side of the chain.
Change gears with your shifters until the chain is on the largest gear of your chain ring and the smallest cog of your cassette. Turn the high adjustment screw clockwise until the inside of the front derailleur cage is 2 millimeters from the chain.
Pedal your bike by hand while changing the front gears from lowest to highest. If the chain doesn't move smoothly between gears, keep tightening. If the chain can't make it onto the gears, loosen the cables slightly.
Rear Derailleur Adjustment
Mount your bike in the work stand. The bike should be positioned in the stand so you can turn the pedals freely.
Shift your chain onto the largest gear on your rear cassette and the largest chainring of the front gears.
Locate your rear derailleur's high and low adjustment screws. They will be two screws side by side toward the back of the derailleur body. The upper screw is the low adjustment screw and the lower one is the high adjustment screw. If you look closely, the screws should be marked with an "H" for high and "L" for low.
Turn the high adjustment screw one-quarter turn clockwise to tighten the cable.
Shift onto the smallest gear on your rear cassette and the smallest gear on your front gears. Turn the low adjustment screw on the rear derailleur one-quarter turn clockwise to tighten the cable.
Pedal the bike by hand as you shift through all the gears on your rear cassette. If the shifting still feels sloppy, tighten the adjustment screws another quarter turn. If the chain can't make it onto one of the outer gears, loosen the cable slightly.
Items you will need
- Bike work stand
- Phillips head screw driver
- Small turns make big differences when you adjust your front and rear derailleurs. Use only quarter turns at a time, check the adjustment and then tighten again if necessary.
- If your chain cannot make it onto a gear, the cable is too tight and you should loosen the appropriate adjustment screw.
- If the chain goes over a gear, it's too loose and needs to be tightened using the adjustment screws.
- Bicycling Magazine's Complete Guide to Bicycle Maintenance and Repair; Jim Langley, 1999
- The Complete Bike Book; Chris Sidwells, 2003
- Park Tool: Rear Derailleur Adjustments
- Thinkstock Images/Comstock/Getty Images