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Worn components will turn a thoroughbred commuter into a clunker. Here are the most likely parts you’ll need to keep it running sweetly.

While your bike might last a lifetime, many of its components won’t. Moving parts wear out. The good news is that it’s permissible to get bike parts through Cyclescheme, which is especially convenient if your bike has an annual bike shop service.

Don’t put off checking over your bike or taking it to the shop before that annual service rolls around if something looks, sounds, or feels wrong. The more common issues are listed below, but this list isn’t exhaustive.



When: It’s worn (elongated) by 0.75% to 1%.

Why: As a chain’s metal rollers wear, the gap between the rivets lengthens so they no longer mesh tightly with the teeth on the cassette and chainrings. Gear shifting becomes sloppy and the chain may slip off the teeth entirely. By the time you notice this, the jockey wheels, cassette, and chainrings may also need replacing. Invest in a chain checker to maximise drivetrain life.

Bicycle Chain Check 

Cassette & chainrings

When: The existing chain has worn by 1% or more (see above) and/or the teeth look like a bit like a shark’s fin and won’t mesh tightly with a new chain.

Why: The chain will slip during gear shifts and sometimes while pedalling hard. If you change your chain soon enough, the cassette and chainrings should last for at least two or three chains. Since chainrings are usually bigger, the wear is distributed over more teeth and they last longer. Changing the cassette or chainrings is an opportunity to alter the gearing.

Derailleur gears 

Derailleur jockey wheels

When: When they start to look like throwing stars or when changing the cassette, whichever comes sooner.

Why: Jockey wheels are plastic and the teeth become pointy rather than square edged as the chain wears them away. At that point, gear shifting becomes sloppy and the chain may fall off.

Bottom bracket

When: The cranks don’t spin freely, or wobble, or feel rough and noisy.

Why: The bearings are too tight, too loose, worn and pitted, or contaminated with grit and dirt. Bottom brackets on road-going bikes can last years; for mountain bikes it’s more like months. Square taper bottom brackets generally last longest and can sometimes be completely overhauled. External bottom brackets and press-fit bottom brackets generally need to be replaced. Press-fits can have a very short lifespan. 

Gear cables

When: The cable outer becomes kinked or split, or gear shifts become stiff or delayed.

Why: Friction between the steel cable and the cable outer will spoil the gear indexing, so when you click the lever the derailleur doesn’t move far enough – especially down the cassette, from big sprockets to smaller ones. The cause can be a damaged outer cable or water and dirt ingress. Try adjusting the gears first.

Gear Cables 


Tubeless tyre sealant

When: It coagulates and dries out, probably within six months of installation.

Why: Tyre sealant needs to remain liquid so that escaping air in the punctured tyre will force it into the hole, where it will solidify. Some sealants are specially designed to stay liquid. Most aren’t.


When: Multiple punctures at once make it uneconomical to patch, or the hole is too big for a patch.

Why: While a tube can be repaired many times with patches, slits longer than 3mm may grow under the patch, making a long-term repair impossible. And some cuts or tears are too big in the first place. New tube time!


When: The tread pattern (if present) is becoming indistinct, there are flat spots on the tread (if there’s no pattern), or the rubber is so worn or cracked you can see the threads in the tyre casing. Also if the sidewall is slashed, or the tyre sidewall starts to separate from the bead.

Why: A worn tyre will puncture more often and won’t grip the road or trail as well. An innertube can bulge out of tyre sidewall cuts, although small nicks in the tread can be plugged with superglue. Replacing a tyre is a good opportunity to fit a different one better suited to your riding.


When: One of them breaks.

Why: Spokes flex slightly as the wheel rotates, more so when they’re insufficiently tensioned. Eventually one may break, typically at the bend when it joins hub. The wheel will go out of true and wobble, rubbing against rim brakes or the frame. Spoke breakage is more common in wheels that are cheap, heavily loaded, or that have fewer spokes.




When: There’s only a thin sliver of pad material left, or the brakes are becoming noisy and less effective.

Why: Once the pad material has worn away, you’ll be down to the metal backing plate. Metal on metal doesn’t stop you effectively and ruins rims or rotors. If your brakes aren’t working well, first check they’re properly adjusted and inspect them while you’re at it. It could be time for new pads.


When: The cable outer becomes kinked or split, or the brakes are stiff and difficult to apply even when you’ve adjusted them.

Why: It’s due to to friction between the cable and the cable outer. The cause is usually a damaged cable outer or water and dirt ingress.

Hydraulic hoses

When: You squeeze the lever and the pads don’t move far enough. Maybe the lever comes all the way back to the handlebar.

Why: Fluid has leaked out and air has got in. The hose itself is probably fine. The problem is what’s inside it. You need to get more hydraulic fluid in and any air bubbles out – a process called bleeding the brake. Occasionally all the fluid may need to be replaced.


Bar tape

When: It’s torn or tatty.

Why: You’ll get a more secure grip on your handlebar. Your bike will look better!