Gears

The most annoying thing whilst riding a bike is when your gears don’t shift smoothly and quickly. No, hang on. The most annoying thing is when drivers sit on your shoulder, neither overtaking nor giving you any room. No! I tell a lie. It’s when the ring pull comes clean off your can of Coke. Wait! It’s actually that random stranger that appears out of nowhere and sucks your wheel, isn’t it?

Image of snapped ring pull

One of the most annoying things whilst riding a bike is when your gears don’t shift smoothly and quickly. This is especially true if the gears are slipping and the chain is rubbing. But alongside the puncture (and possibly before it) it is the most common ailment of the day to day cyclist.

If you haven’t done so already, it is time to master adjusting your gears.

Image of Chain Drive

Most bikes will have multiple cogs on the rear wheel and the chainset (the bit the pedals attach to with all the teeth). In both positions there is a derailleur mechanism that shifts the chain from one cog to another, changing the gearing. Each of these can be adjusted to create a smooth gear shift.

Most issues arise with the rear derailleur, mainly because it is the one most used.

Adjusting the rear derailleur

Normally there are two limiter screws, marked H (high) and L (low). Sometimes they are not marked, which is a pain because you will have to experiment to find out which is which. H adjusts how far the mechanism can move in one direction (the higher limit) and L the other direction (the lower limit). You will need to use a screwdriver to turn the screw to adjust the outer limits. Each mechanism will have a slightly different setup so it is impossible to say what the effect of screwing clockwise or anticlockwise will be. One will shift the limit out, the other in. Best advise it to make small adjustments and make a note of the effect.

Image of Limiter screws with lables

Test the outer and inner limits by changing to your smallest and largest cogs. If the limits are set correctly the chain will sit on the middle of the cogs with no rubbing. If the limits are set too far the chain could jump off the cassette completely, which is not desirable.

Once you have the limits set, click through the gears. If the gears are not running smoothly from cog to cog you will need to adjust the cable tension. When you shift to a bigger cog (easier gear) you do so by pulling the gear cable (via a lever or twist grip). Moving to a smaller cog (harder gear) is achieved by releasing the cable. You can experiment with this by pulling on the cable where it is exposed on the frame whilst the pedals are turning and noting the effect.

Your gear shift mechanism is pre-calibrated to give enough pull (or to release enough tension) to shift the chain between cogs. You do not need to worry about this. But you do need to get the correct tension in the cable to line it up perfectly with the cogs in the first place.

Click your gear mechanism through your gears until the chain is (or should be) on your smallest cog. Now, whilst turning the pedals, adjust the barrel tensioner (at the end of the outer cable casing where the cable enters the derailleur) by turning it clockwise or anticlockwise. As you turn it the cable is tensioned (or released) by small amounts making the derailleur shift in or out. I find the easiest way to remember which way to turn the barrel is to turn it in the direct I want the derailleur (and by consequence the chain) to move. If I want the chain to move towards the bigger cogs I turn the barrel in that direction and vice versa (so rolling your thumb away from you to move to a bigger cog and towards you for a smaller cog). You need to turn the barrel until the chain is on the smallest cog and running smoothly with no noise. You can roll it back and forth to find the best position.

Test through your gears by shifting up and down the cassette a few times. All the gears should change smoothly if the first gear is set correctly because the shift between gears is pre-calibrated.

If some of the gears do not shift properly then this could be a sign of some other issue:

  • Your chain could be worn and need replacement.
  • If it is regularly not changing on the same gears it is probably a sign that the teeth on those cogs are worn and that you need to replace the cassette (it is not cost effective to change individual cogs, even if this is possible).
  • Your cable may be sticking or stretched and either needs some attention or should be replaced.

There is a third adjustment screw on the rear derailleur which pushes against the frame of the bike. This is known as the ‘B tension’ (or angle adjustment) screw. Adjusting this screw should move the position of the top jockey wheel (small wheels on the derailleur) in relation to the cogs on the cassette.

Ordinarily you should not have to adjust this screw but you might need to if you have changed the cassette to a different size (e.g. taken off an 11-25 and replaced it with a 12-32). To adjust, turn the screw to position the jockey wheel close to the cassette. This should ensure a crisp gear shift. If you can adjust whilst pedalling (bike on a stand) then you should be able to find the sweet spot by adjusting back and forth.

Adjusting the front derailleur

Before making any adjustments to your front derailleur shift the gears so that the chain is on the inner (smallest) ring on the front and the inner (largest) cog on the rear. Then release the tension from the cable by turning the barrel adjuster (this should be located somewhere along the cable run) until the cable is slack.

Position

Your front derailleur can easily be knocked out of position, for instance, by your foot. It should be positioned 1-3 mm above the large chain ring so that it is parallel with the chainring. If it is not, loosen the screws attaching it to the frame slightly and realign it.

Set the inner limit

As with the rear, there should be two (hopefully labelled) limiter screws on the front derailleur. Locate and turn the inner limit screw until the inner part of the derailleur cage is as close as possible to the chain without rubbing.

Image of Front Derailleur Limiter Screws

Tighten the cable

Tighten your cable by releasing the bolt anchoring the cable, pulling the cable tight and then retightening the bolt.

Set the Outer Limit

Shift gears so that the chain is on the outer (largest) ring on the front and the outer (smallest) cog on the rear. Locate and turn the outer limit screw until the outer part of the derailleur cage is as close as possible to the chain without rubbing.

Test

Shift the front derailleur a few times to make sure it is shifting the chain properly from ring to ring. If it is not, the most likely cause will be incorrect tension in the cable and you may need to re-tension it slightly with the barrel adjuster. If the problem persists it may be that you need to clean and lube your cable or possibly replace it. It is also worth checking the teeth on your chain rings – if they are shaped like sharks teeth (slightly hooked rather than symmetric) then they are worn and this can cause a delay in down shifting (to a smaller chain ring).

Image of Chainring Wear

Breakages

If your rear derailleur breaks on a ride it can be game over. But, if you have the tools, you can remove it completely from the bike then shorten the chain so that it sits on one of the middle cogs. You will only have one gear on the rear but you will be mobile. The choice of cog should depend on your pedalling power and the terrain you need to cover to reach a bike shop.

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