A poorly adjusted derailleur can be the difference between a great ride and throwing your bike into the bush with frustration. Having gears that are crisp and reliable will make you ride better, be more efficient and wear out fewer parts. The concept of setting up your rear derailleur can be daunting yet after breaking it down step by step, you will see that it isn’t so bad.
On a derailleur there are four means of adjustment which will each change a different aspect of your shifting. In this article I will break down each of the adjustments into what they control, and how to set them accordingly. The four types of adjustment are:
- B – Tension Adjustment
- High Limit Screw
- Low Limit Screw
- Cable Tension
B Adjustment
The First means of adjustment is probably the least understood part of any bicycle. The B – Adjustment. If this screw is set up correctly, it is likely that you never even knew it existed. If not then your bike has likely never shifted correctly. The B-Tension adjustment controls the height of the upper pulley in relation to the cog.Winding out this screw will decrease the gap between the pulley and cog while winding it in will increase the gap. If the B adjustment is wound too far in, the derailleur will have a large gap and have a tendency to jump gears. If the adjustment is too far out then the jockey wheel will sandwich the chain between the cog and pulley resulting in a grinding/rubbing sound. The optimal position is where the pulley clears the cog and chain by approximately 2-3mm.
B Adjustment Wound Too Far In
B Adjustment Wound Too Far Out
Correct B Adjustment
The second and third aspect of derailleur adjustment are the two limit screws. These adjustments change the extremes of how far the derailleur can move. If your chain has ever gone into your spokes, you can likely blame an incorrectly adjusted limit screw. Both limit screws are labeled with an H for high and a L for low.
Sram Limit Screws
Shimano Limit Screws
Every derailleur has two limit screws, a high and a low. The easiest way to remember which is which is to think in terms of high speed vs. low speed. The H, or high speed limit screw will control how far towards the outside or smallest cog your derailleur will travel. The L, or low speed adjustment will control how far up towards your spokes the derailleur will travel.
Limit Screw Adjustment
Winding inward (clockwise) both the the high and low limits will shift the derailleur towards the center of the cog. For example, if your derailleur is traveling into the spokes, you will need to wind in the low limit. If you are unable to shift from 2nd into first even manually pushing the derailleur, the low limit needs to be wound out. on the other side, if the chain is falling off of the smallest cog, you will need to wind in the high limit, while if you can not shift from 8th into 9th gear, you will need to wind out the high limit.
On a correctly adjusted derailleur, the pulley wheels will line up directly with the highest and lowest cogs.
Properly aligned High Limit
The last aspect of derailleur adjustment is cable tension. The cable that runs from the shifter to the derailleur is an extremely important aspect of your bike. The tension of this cable will determine if your gears will shift or cause you endless frustration.To adjust the cable we can break it down into a few simple steps.
- Shift into the smallest cog which is your hardest gear.
- Wind in your barrel adjustment in all the way and then out one half turn. This is for both the handlebar barrel and the derailleur if you have one.
- Undo the derailleur cable fixing bolt and pull the cable tight without moving the derailleur.
- Tighten the fixing bolt without letting any slack into the cable.
Cable Fixing Bolt
At this point your derailleur should be close. To make minor adjustments you will now use the barrel adjuster. When shifting, if the derailleur will not shift up, into an easier gear you will need to wind out the barrel adjuster. Start to turn the barrel in a counter-clockwise rotation 1/4 turn at a time until the gear changes smoothly. If by chance the derailleur does not shift down, into a harder gear, you will want to turn the barrel in a clockwise rotation 1/4 turn at a time until the shift is made.
Barrel Adjuster
As you can see, there is a fair bit to correct derailleur adjustment. Really though, it breaks down into four adjustments and a little bit of patience. If you have any input of adjustment, comment, ask questions, provide your two cents.
Until next time,
Dustan
