Accurate front derailleur indexing is critical to maintaining fast, fault-free front shifting. As with all indexed gears, good performance is down to properly adjusted front derailleur limits and zeroing in on the right cable tension. Front derailleurs work hard to deliver the chain across big gaps in comparison to rear derailleurs and they need a little bit of TLC to keep them sweet. Here's how.
Our guide below shows you what we believe is the best method to index your front gears. We've included a list of the tools and materials that you will need to complete the job and in some cases where you can buy them. If there are others that you prefer then feel free to let everybody know in the comments.
Tools & Materials
•Small Phillips screwdriver
1. Before you get too worked up about cable tension it's vital to know that your front derailleur is positioned accurately. The gap between the lower edge of the front derailleur cage and the top of the outer chainring teeth should be 1-3mm for optimal performance. The inner plate is shaped to lift and push the chain at this height. Lower and you'll foul the teeth on the outer ring, higher and the delivery will be slow and vague.
2. Check for cage alignment as well. Direct mount front derailleurs will automatically be lined up accurately as they're bolted direclty to the frame - which should be square. For band clamp front derailleurs, the cage should be exactly in line with the centre line on the chainrings. Shift the chain across the chainrings to see that this is the case. Make any angle adjustments at the band clamp, but be careful not to change the clamp height when you do, or you might negatively impact the cage height.
3. You'll need to release the cable tension in the front derailleur cable. Turn the barrel adjuster all the way clock wise to release any slack in the system. They give it a full turn anti-clockwise to give some adjustment lee-way in both directions.
Setting cage stops
4. To set your inner limit, first shift your front derailleur into the small chain ring and your rear derailleur into the largest cog. Adjust the inner limit screw with an appropriately sized screwdriver. Take care as the heads of the screws are easily damaged - making subsequent adjustments harder. The screw is usually marked by a small letter 'L' for Low. You want to turn the inner limit screw until the inner part of the derailleur cage is as close as possible to the chain without rubbing (as indicated by the tip of the screwdriver in this shot).
5. To set your outer limit, first shift your front derailleur into the large chain ring in the front and your rear derailleur to the smallest cog. Adjust the outer limit screw with an appropriately sized screwdriver. Take care as the heads of the screws are easily damaged - making subsequent adjustments harder. The screw is usually marked by a small letter 'H' for High. You want to turn the outer limit screw, found on the top of the front derailleur body, until the inside edge of the outer cage plate of the front derailleur is as close as possible to the chain without rubbing. 1-2mm is about right. (Where the tip of this screwdriver is pointing...)
Reset cable tension
6. Reset the overall cable tension at the cable anchor point. Use a cable puller like this BT-2 Park Tools one which grabs the cable and allows you to make fine adjustments without fraying trimmed cables. The locking feature on this particular model means once set and locked, you could let it go, while you tighten the anchor bolt.
Check shift speed
7. When you've made your cage limit adjustments and set the cable tension, you can give the cranks a turn and operate the front shifter. You should now have a front derailleur which lifts, pushes or drops it quickly and cleanly to the adjoining ring. If the upshift is a little slow you can add tension to the barel adjuster.