ADJUSTING DERAILLEURS
By Steve Bowen

This month I will discuss adjustment of the front and rear derailleurs.

To make adjustments to the derailleurs, it is necessary to be able to raise the rear wheel off the ground so it can spin freely while you turn the pedals. There are a number of ways to do this, but the simplest is to get some kind of repair/work stand. Park Tools and Pedros both make reasonably priced (around $120) home work stands that will hold a bike off the ground at a height that makes it easy to work on the bike. You can also hang a bike from a wall rack or car carrying rack, although this makes things a little more difficult. There are also several variations of a gadget that raises the rear wheel just a few inches off the ground, high enough for simple repair work. These are around $25.00 and don’t take up much space.

The most common symptoms of derailleur misadjustment are:

• Chain skipping between gears on the rear;
• clicking noises from the chain in the rear of the bike;
• hesitation or missed shifts when changing gears;
• chain rubbing on the front derailleur; and
• the chain coming off the front chainrings.

There are 3 general types of derailleur adjustment: (1) checking and setting the inner/outer travel of the derailleur, (2) adjusting the tension on the cable that runs from the shifter to the derailleur and (3) checking and setting the horizontal angle of the derailleur. Here’s how the process works:

1. Shift the bike into its lowest gear, with the chain on the smallest front gear and largest rear cog. All of the following checks and adjustments should be done wile turning the pedals at a relatively high cadence.

2. Check that the front derailleur cage is exactly parallel with the chainrings. If not, loosen the screw on the clamp that holds the front derailleur to the seat tube and rotate it until the cage is parallel. Be careful not to move the derailleur up or down whil doing this. The vertical gap between the bottom of the front derailleur cage and the teeth of the largest chainring should be 2-5mm.

3. Once the derailleur is aligned, check the gap between the inside of the chain and the rear plate of the front derailleur cage. There should be just enough gap to see between them, about 1-2 mm.

4. If there is too much gap, or if the chain rubs on the inner derailleur cage, figure out which of the 2 small Phillips head screws on top of the front derailleur change the inner limit of travel (the screws are in different positions on different types of front derailleurs, so you’ll have to figure out which is inner and which is outer travel. If there is too much gap, the chain can come off the inside of the small chainring when you downshift, and if there’s not enough gap you may have trouble getting the chain to go down into the small ring, or the chain will rub on the derailleur cage.

5. With the chain still on the small front ring and large rear cog, check pulley wheel on the rear the rear derailleur. The teeth should be horizontally lined up with the teeth on the largest rear cog. If not, turn the low gear trim screw on the derailleur (on Shimano derailleurs, the one closest to where the derailleur is screwed into the frame) to line them up.

6. When this is done, sight down the length of the rear derailleur cage to see if the outer pulley is lined up with the inner pulley. If not, you have a bent derailleur hanger or a bent derailleur cage (or both) and this is a job for a good bike shop. If it looks OK, then shift the bike into its highest gear (large front chainring, small rear cog.)

7. Go back and look at the gap between the front derailleur outer cage and the chain. If the gap is too small or the chain rubs on the outer cage, find the front derailleur cable where under the downtube and pull. If you are able to make the front derailleur cage move farther away from the bike, there is too little tension on the cable. On some bikes there is a front derailleur cable tension nut on the downtube just behind the head tube. Turn the adjusting collar counter clockwise (standing in front of the bike and looking past the headtube towards the down tube) until the cage moves against its travel screw and you have the proper gap between the outer cage and the chain.

8. If the cable already has enough tension to pull the front derailleur cage as far away from the bike as it will move and the chain still rubs, you need to loosen the travel limiter screw, keeping tension on the front derailleur cable, until you have a 1-2mm gap. If you make the front derailleur cable tension too high, the chain may have trouble dropping into the smallest chainring.

9. Go back to the rear derailleur and check to see if the pulley teeth on the derailleur cage line up with the teeth on the smallest rear cog. If not, turn the adjusting screw (on Shimano rear derailleurs, the one farthest from the pivot bolt that secures the derailleur to the frame) until the teeth line up.

10. Now you are ready for the most common derailleur adjustment, the one that most frequently causes problems. With the bike still in its highest gear, shift up one gear. The chain should move easily to the next larger cog. If it hesitates, increase the tension on the cable by turning the adjusting collar at the back of the derailleur where the cable goes into the derailleur. Looking at the derailleur from behind the bike, turn the collar conter clockwise one or two clicks at a time until you get the chain to move smoothly from the highest gear to the next one. If the chain wants to overshoot the second cog with one click of the shifter, the cable tension is too high. Turn the adjuster clockwise to loosen the cable, or use the adjusting barrel on the downtube behind the headtube.

11. Once you get the chain to shift smoothly up one gear, check the whole range of shifting in the rear. The most revealing area of slightly wrong cable tension is in the middle of the rear cog set. Even if the rear derailleur shifts smoothly at the ends of the cog set, the chain may make noise in the middle. Adjust the tension collar a little bit at a time until the noise goes away.
    
12. If you can’t get rid of noise or mis-shifting in the middle of the cog set even when the high and low shift smoothly, this is probably a sign of a bent derailleur hanger (see above and take to your local bike shop.)

13. Finally, road test and try to stress the drivetrain a little by going up a steep hill in a higher gear than normal. This will reveal shifting problems that weren’t evident without any load on the drivetrain. If the chain slips badly under load even when the bike is shifting correctly, it is likely that your chain and/or cog set are worn and need to be replaced.