Mechanical Services & Maintenance

Derailleurs and Shifting:

Adjusting the Front Derailleur

Adjusting the front derailleur on a bicycle can seem like a tricky affair. There are screws to adjust, the clamp can give any combination or height and angle you can imagine, and then you have the cable anchor bolt. How do all of these adjustments relate to each other?

The first adjustment is to get the derailleur mounted correctly with the proper angle and height above the chainring teeth. The height can be defined by a 1-3 mm gap from the top of the chainring teeth to the bottom or the derailleur cage. Once you have the height dialed in, you want to make sure the angle is correct before tightening the clamp bolt. For best shifting results, align the outer cage of the derailleur parallel with the outer chainring. This will insure the derailleur moves efficiently between gears.

The limit screws are the most confusing part of the front derailleur. Most people are not sure what they do and when things are not shifting properly, they give these a turn and things get worse. The screws are there to simply limit the movement of the derailleur in each direction so it will not shift your chain over the big ring or drop the chain off the small ring and on to the frame. Once the limit screws are set properly, they should not require further adjustment and any sluggish shifting or rubbing issues are usually related to cable tension.

You will notice most derailleurs have an L or H beside the screws. The L signifies the low limit screw. This will limit how far the derailleur travels towards the frame. The more you tighten the screw, the less movement the derailleur will have towards the frame. The H signifies the high limit screw. This will limit how far the derailleur travels away from the frame. The more you tighten this screw, the less movement the derailleur will have away from the frame.

Once you have the limits screws adjusted properly, the only step left is to connect the cable. When the low limit screw has been adjusted properly, the cable tension should be very close to perfect. Should more adjustments be needed, this can be done via the barrel adjuster on the frame or shifter.

Below is a quick guide to adjusting the front derailleur. Armed with the knowledge of how the derailleur works, this is now a simple and straight forward process.

All screw adjustments should be done in quarter turn increments.

Tools needed:

• Philips screwdriver #2
• 5mm Hex wrench

1. Check the low and high limits. Shift to the largest cog on your cassette and smallest chainring up front. There should be 1mm of space between the inside of the derailleur cage and chain. If there is not, turn the low limit screw (usually the inner-most screw) in or out until the correct distance is achieved. Then, shift to the smallest cog on your cassette and the largest chainring up front. The outer side of the derailleur cage should be 1mm away from the chain. If not, adjust the high limit screw.

2. Set cable tension. This is the quickest way to get precise shifting. On road bikes, shift to the small chainring up front and the largest cog on the rear cassette. Loosen the cable anchor and adjust the inner limit so that the chain is 1mm away from the chain. Pull the cable taut and reattach. If the chain hesitates when going to the big chainring, increase cable tension by turning the barrel adjuster out.

Keep the derailleur clean. Grit that builds up on the body can work its way into the pivots and cause premature wear, as well as sloppy shifting. Wipe the derailleur down with solvent on a rag. Let the derailleur dry for 10-15 minutes then lubricate the pivots.