Breakdowns and Repair: What Fails Most and How to Fix It

Maintenance fundamentals

Most bicycle failures don't come out of nowhere. A chain stretches little by little over thousands of kilometers, brake pads get thinner with every stop, and shift cables stretch slightly over the first few hundred kilometers, throwing off the indexing. That's why the heart of maintenance is less a 'repair skill' than a 'habit of noticing.' An unfamiliar sound, a strange vibration, pedals that feel a little heavier — these are all signals from the machine, and the earlier you read them, the simpler and cheaper the fix.

The guides in this chapter rest on three principles. First, suspect the simplest cause first. If shifting skips, check cable tension and chain wear before taking the derailleur apart; if you hear a click, check the pedals, saddle and quick release before pulling the BB. Even in real workshops, the first impression that 'an expensive part has failed' turns out to be wrong far more often than not. Second, change only one thing at a time. Turn several bolts at once and you'll never know which one fixed the problem — or which one created a new one. Third, when in doubt about anything safety-critical, take it to a professional. Brakes, steering (headset, stem, fork) and wheel retention are places where a mistake leads straight to a crash.

One more thing to remember: specified torque. Modern bikes are full of parts that 'break if you overtighten them' — carbon handlebars, aluminum stems, thin lightweight bolts. If a bolt or part is marked with something like '5Nm' or 'MAX 6Nm', that is the manufacturer's spec. If you don't have a torque wrench, at the very least learn the feel of turning a small hex key with finger strength alone. Conversely, high-torque fittings such as pedals, crank fixing bolts and cassette lockrings can work loose on the road if undertightened.

Breakdown heatmap: where do things go wrong most often?

Ask a mechanic "What repair do you see most?" and you'll get much the same answer every time. Flats are far and away the most common, followed by the chain and drivetrain, brake pads and shifting adjustment. Frames themselves, on the other hand, rarely fail short of a crash. The heatmap below expresses these general trends as color temperature: the redder the spot, the more often it causes trouble. Tap any area to see its symptoms, causes, difficulty and expected cost, and jump to the matching repair guide in this chapter.

What stands out on the heatmap is that the red zones are almost all 'wear parts'. Tires and tubes, chains, brake pads and cables are designed to wear out in the first place. Because they wear in place of everything else, expensive parts like the frame, hubs and rims can last a long time. In other words, replacing wear parts on time is the most economical maintenance there is. The yellow zones — BB, headset, seatpost — fail less often, but the source of a noise there can be tricky to track down, so they tend to cost more time and money.

Pre-ride ABC quick check

Many crashes and breakdowns can be prevented with a one-minute check before you ride. The 'ABC Quick Check', widely taught in English-speaking cycling education, runs through the key areas in an easy-to-remember order: A for Air, B for Brakes, C for Chain & Cranks, and finally Q for Quick release & Quick check. Tick off the items on the card below one by one. Once it becomes routine, it takes less time than putting on your helmet.

A quick-release lever should feel firmly closed. The right amount of resistance leaves a faint imprint on your palm as you close it; if it flips over easily with your fingers, tighten the nut on the other side a little more. Spinning the lever round and round like a wing nut is a common mistake — done that way, it won't clamp securely. Thru-axles also need to be tightened to spec, and aligning the lever along the fork leg reduces the chance of a branch catching it and flipping it open on the trail.

Symptom diagnoser: tracing causes from sounds and feel

A mechanic tracks down a fault much like a doctor taking a history. "When does it make the noise?" "Only when you brake?" "Once per wheel revolution, or once per pedal stroke?" Narrow the suspects down with questions like these and most problems are pinned down within a few steps. The diagnoser below follows exactly that line of thinking. Pick a symptom and answer yes or no, and it will point you to the most likely cause, the fix and the relevant guide. Safety-critical results are flagged 'Take it to a shop'.

As the diagnoser shows, the 'rhythm' of a noise is a powerful clue. A noise that repeats with each wheel revolution points to the wheel, tire or brake rotor; one that repeats with each crank revolution points to the pedals, cranks, BB or chainrings. A continuous whirring that tracks chain speed is most likely a derailleur or chain problem. If the noise is hard to reproduce, lean the bike against a work stand or wall and turn the pedals by hand, or ask a friend to ride it while you walk alongside and listen. When you're the one riding, sound traveling through the frame can easily make it seem to come from the wrong place.

Basic tools to keep at home

There's no need to buy every tool at once. Most of the guides in this chapter need only the 'Basic set' below; add the rest when you decide to take on that job yourself. The low-quality hex keys in cheap tool kits tend to round off bolt heads, so we recommend buying good-quality 4, 5 and 6mm hex keys and a T25 Torx key separately, since those are the ones you'll use most.

Fixing flats and replacing tubes

The flat tire is the king of bicycle breakdowns. Luckily, it's also the easiest repair to learn. Flats on tubed (clincher) tires fall into two main types: the puncture, where glass, wire or a thorn goes through the tire and holes the tube, and the snakebite (pinch flat), where you hit a curb or rock hard with too little pressure and the tube is pinched against the rim edge, leaving two holes side by side. Different causes call for different prevention, so make a habit of checking the shape of the hole.

On the road it's quickest to swap in a spare tube and patch the punctured one calmly once you're home. A well-patched tube is as good as new. Holes right next to the valve or long tears, however, don't hold a patch well, so replace the tube in those cases.

Step-by-step repair

1. Remove the wheel. For a rear wheel, shift into the smallest cog first to make it easier to take out of and put back into the chain. With rim brakes, open the caliper's quick-release lever so the tire clears the pads.
2. Let out all remaining air and loosen the beads. On a Presta valve, unscrew the small nut at the tip and press it to release the air. Squeeze both sides of the tire firmly by hand to push the beads toward the center channel of the rim.
3. Hook a lever in opposite the valve. Slide one lever under the bead, pry it up and hook it on a spoke; insert a second lever about 10cm along and slide it around the rim to free one bead.
4. Remove the tube and find the hole. Put in a little air and feel for the leak with your ear and cheek, or dunk it in water and look for bubbles. Practice with the 'Find the puncture' game below.
5. Always remove the cause. Line up the tube's valve with the tire's logo and you can find the spot inside the tire that matches the hole. Run your fingertips slowly around the inside and pull out anything embedded. Skip this step and your new tube may go flat again within minutes.
6. Patch it, or ready a new tube. Scuff the area around the hole with sandpaper, spread a thin layer of rubber cement, wait until it loses its shine, then apply the patch and press hard. Self-adhesive patches need no glue but are best treated as a temporary fix.
7. Fit the tube and seat the bead. Inflate the tube just enough to give it shape and insert the valve first. Starting at the valve, push the bead in with both hands, finishing opposite the valve. Finish by hand without levers if you can, so you don't pinch the tube.
8. Inflate while checking the bead seat. When it's about half inflated, check that the molding line on the sidewall sits evenly parallel to the rim all the way around, then pump up to the recommended pressure.

Topping up tubeless sealant

A tubeless tire holds air between the tire and rim directly, with no tube, and the liquid sealant inside plugs small holes on its own. That means you hardly have to worry about snakebites even at low pressures, and it shrugs off punctures so well that a small thorn may go unnoticed on a ride. But sealant evaporates and hardens into clumps over time, so unless you top it up regularly it won't seal a hole when you actually need it to. Top-up intervals vary with the product and climate but are generally 2–6 months, and sealant dries out faster in hot, dry summers.

1. Check how much is left. Hold the wheel near your ear and shake it, listening for a sloshing sound. If you hear almost nothing, it has dried out. If there are lots of old, rubbery clumps, it's best to unseat one bead and remove them.
2. Let the air out and remove the valve core. Turn the wheel so the valve is at 4 or 8 o'clock, then take out the core with a core remover.
3. Shake the sealant and inject the right amount. The fine particles in sealant settle, so shake the bottle well before injecting. Around 20–40ml for road tires and 60–120ml for MTB is a common guideline, but always follow the product's recommended amount.
4. Refit the core, inflate and spin. Rotate and tilt the wheel in several directions so the sealant spreads evenly over the whole inside of the tire and along the bead.

Cleaning and lubing the chain

The chain lives in the harshest environment of any part on a bike. Sand and dust from the road stick to the oil and turn into an abrasive paste that grinds away between the rollers and pins, elongating the chain. So the surest way to extend chain life isn't buying an expensive chain but keeping it clean and lubricating it properly. A shiny, black chain isn't well cared for — it's over-oiled. The ideal chain is clean and almost dry on the outside, with lubricant only inside the rollers and pins.

1. Wipe off surface grime. Hold the chain lightly in a rag and backpedal to strip dirt from the surface. If it's very dirty, spray on degreaser, scrub with a brush, rinse with water and let it dry completely.
2. Put one drop on each roller. On the inner face of the lower run of chain, backpedal slowly and put one drop on each roller. Using the quick link as a start marker lets you count exactly one lap.
3. Let it soak in. Turn the cranks a few dozen times, shift through a few gears, then leave it for a few minutes. Some products recommend several hours of drying time.
4. Wipe the outside thoroughly. Oil left on the outside does nothing for lubrication and only attracts dirt. Wipe with a clean rag until the surface is almost dry.

Lubricants fall broadly into wet, dry and wax-based types. Wet lube resists rain and water and lasts longer but picks up dirt readily; dry lube stays clean but washes off easily in the rain. Wax is the cleanest and causes the least wear, but the initial prep is a hassle and you need to stick to the reapplication schedule. If you mostly ride on the road in fair weather, dry lube or wax is a safe bet; if you often ride in rain and mud, go with wet.

Measuring chain wear and replacing the chain

We often say a chain 'stretches', but the metal plates don't actually get longer. The pins running through the rollers and the bushings around them wear against each other, opening up tiny gaps; hundreds of those gaps add up and lengthen the pitch (pin spacing) of the whole chain. A worn chain no longer meshes precisely with the cassette and chainring teeth, grinding away one face of each tooth until the teeth are deformed into shark fins. At that point, even a new chain will slip and 'skip' on the worn cassette.

Chain pitch is 1/2 inch (12.7mm), so on a new chain the distance from one pin center to the pin center 24 pitches away is exactly 12 inches (304.8mm). Generally, replacement is recommended at 0.5% elongation for narrow 11-speed and up chains and 0.75% for 10-speed and below. Over 12 inches, 0.5% works out to about 1.5mm and 0.75% to about 2.3mm. Beyond 1%, the cassette has likely worn along with it, and a new chain alone probably won't fix things. Commercial chain checkers let you check these thresholds quickly — though it's worth knowing that some simple 'drop-in' checkers also measure roller wear and so tend to overstate elongation somewhat.

Replacing the chain

1. Set the length. If the old chain was the right length, lay the new one alongside it and cut it to the same number of links. If you're not sure, use the classic method of 'wrapping it around the largest chainring and largest cog, bypassing the derailleur, and adding one link (2 pitches)' — or, for the latest 12-speed systems, follow the manufacturer's method.
2. Remove the old chain. If it has a quick link, squeeze it open with the dedicated pliers; if not, push out a pin with a chain tool.
3. Route the new chain. It has to follow the correct path through the front derailleur cage and between the rear derailleur pulleys. In particular, check that it passes inside the small tab on the rear derailleur cage. If the chain has a directional marking (logo side), face it outward.
4. Connect it and check. Fit the quick link and press on the pedal so it snaps shut with a click; if you joined it with a chain tool, check that the pin protrudes evenly on both sides and that there are no stiff links. Run through every gear once.

Replacing brake pads and adjusting rim brakes

Brakes are the most important safety system on a bike, and the pads are consumables that sacrifice themselves to do the job. Rim brake pads have grooves to channel away water, and these double as wear indicators: when the grooves are so shallow they're barely visible, it's time to replace them. Disc brake pads have friction material bonded to a metal backing plate, and each manufacturer's threshold differs slightly — Shimano recommends replacement when the friction material is 0.5mm or less, SRAM when total thickness including the backing plate is about 3mm or less — so check your manual.

Replacing disc pads

1. Remove the wheel and take out the pads. Pull the caliper's pad retaining pin (or clip) and slide the pads out the bottom or top of the caliper. Note which way the spring between the pads faces as you remove them.
2. Push the pistons back. Using a pad spreader or a clean plastic tire lever, press the pistons straight back all the way. Avoid metal screwdrivers, which can damage the pistons. If a piston won't go back easily, or only one side comes out, that's a sign the brake needs bleeding or caliper service.
3. Fit the new pads and align the caliper. Insert the pads with the spring and refit the retaining pin. With the wheel installed, hold the lever on while tightening the caliper mounting bolts alternately — this makes it easier to center the caliper over the rotor.
4. Bed in the pads. On a safe, flat stretch, brake firmly from about 20–25km/h down to walking pace 10–20 times. Don't come to a complete stop, and pause in between so the rotors don't overheat. Bedding in transfers pad material evenly onto the rotor surface, bringing out full braking power and quiet operation.

Rim brake pads and adjustment

When replacing rim brake pads, the first priority is setting the height so the pad meets the center of the rim's braking surface and doesn't stray onto the tire or below the rim. A pad touching the tire sidewall can tear the tire, while one set too low can, as it wears, slip down toward the spokes and suddenly lock the wheel. Squealing is usually cured by toe-in — angling the pad so its front edge makes contact first — and lever free play is adjusted with the barrel adjuster on the lever or caliper. After changing pads, also check that the caliper opens evenly on both sides, i.e. that it's centered.

Bleeding hydraulic disc brakes: an overview

In a hydraulic disc brake, pulling the lever makes the master cylinder push fluid that moves the caliper pistons. If air bubbles get into this circuit, the air compresses and the lever goes spongy, sometimes pulling all the way to the handlebar. Bleeding removes air and old fluid from the circuit and refills it with fresh fluid. It's generally done once a year, or whenever the lever feel changes.

The most important thing is the type of fluid. Many brands — Shimano, Magura, Tektro and others — use mineral oil, while most SRAM products, Hayes, Formula and others use DOT fluid, the same family as automotive brake fluid. Even within one brand, though, it can differ by model, so always check the marking on the lever or caliper and the manual. The two fluids use seals made of different materials, so putting in the wrong one can swell or damage the seals and ruin the entire brake. DOT fluid also damages paintwork, can irritate skin and absorbs moisture, so it's best not to use a bottle that's been open a long time.

The exact bleed procedure varies considerably from brand to brand. Shimano typically has you fit a funnel at the lever and push fluid up from the caliper, while SRAM connects syringes at both ends and pushes pressure back and forth. You need a dedicated bleed kit, bleed blocks and the correct procedure, so if it's your first time we recommend doing it with someone experienced or leaving it to a shop.

Rear derailleur adjustment: barrel adjuster, limits, B-tension

Most problems like sluggish shifts, skipping a gear, or rattling in certain gears aren't failed parts but adjustment issues. A mechanical rear derailleur has four adjustments. The H limit screw sets the outer limit of travel so the chain doesn't fall off past the smallest cog; the L limit screw sets the inner limit so the chain doesn't go past the largest cog into the spokes. The barrel adjuster fine-tunes cable tension to line up each gear position (the indexing), and the B-tension screw adjusts the gap between the upper guide pulley and the cogs.

The order of adjustment matters too. First check that the derailleur hanger is straight — if it's bent, no adjustment will get every gear right at once. Next, set the limit screws with the cable tension released, set the indexing with cable tension, and finally check the B-tension on the largest cog. Some of the latest 12-speed systems have you set B-tension first with a dedicated gauge, so follow the manufacturer's procedure.

1. Set the H limit. In the smallest cog, adjust the H screw so that, viewed from behind, the guide pulley lines up directly with the smallest cog.
2. Set the L limit. Set the L screw so the derailleur can't move past the largest cog when you push its body inward by hand. Get this wrong and the chain can drop into the spokes, wrecking both the wheel and the derailleur.
3. Cable tension (indexing). Shift up one gear at a time from the small cog. If it's slow to climb to a larger cog, loosen the barrel adjuster (usually counterclockwise) to increase tension; if it's slow to drop to a smaller cog, or rattles against the next cog up, tighten it to reduce tension. Change it a quarter turn at a time and check.
4. Check B-tension. In the largest cog, set the gap so the guide pulley clears the cog teeth but isn't too far away. Too close and it chatters; too far and shifting gets sluggish.

Wheel truing: an overview

A wheel is a structure in which dozens of thin spokes pull the rim toward the hub under high tension. When the tension of a single spoke changes, the rim is pulled toward it or pushed away and starts to wobble from side to side — what we call a wheel being 'out of true'. Side-to-side wobble (lateral), up-and-down hop (radial), the rim's side-to-side position relative to the hub center (dish), and the balance of overall tension are the four elements of wheel maintenance.

A slight side-to-side wobble can be trued at home. With the wheel in the frame, spin it slowly and use a brake pad or the end of a cable tie as a reference point to find where the rim pulls to one side. At the middle of that section, tighten the spoke going to the opposite flange a quarter turn and loosen the spoke on the same side a quarter turn. The trick is not to turn them much at once, but to repeat in small increments. Nipples are standard right-hand threads, but because you're looking at the nipple from the hub side rather than from the outside of the rim (tire side), tightening will feel counterclockwise — keep that in mind.

Checking headset play

The headset is the set of bearings that lets the fork turn smoothly inside the frame. When play develops, you feel a 'clunk' up front when you brake; leave it and the bearing races get damaged, progressing to indexed steering, where the bar 'clicks' into certain positions. Overtighten it, on the other hand, and the steering gets stiff, hurting straight-line stability.

1. Check. Hold the front brake on firmly and rock the bike back and forth while wrapping your other hand around the upper cup at the top of the head tube to feel for movement. Then lift the front wheel and turn the bar slowly from side to side to check for any catching points.
2. Loosen the stem clamp bolts. On a typical threadless headset, you must first loosen the side bolts where the stem clamps the steerer so that the top cap adjustment reaches the bearings.
3. Preload with the top cap bolt. Tighten the top cap bolt gradually until the play disappears. This bolt is for preload, not for clamping, so there's no need to crank it down.
4. Align, then torque the stem bolts. Line the stem up with the front wheel, tighten the side bolts alternately to the specified torque, then check play and rotation again.

Tracking down BB and other creaks

A 'tick, tick' with every pedal stroke is one of the most maddening problems a rider can have. The BB (bottom bracket) usually gets the blame, but more often the culprit is the pedal bearings or threads, cleats, chainring bolts, saddle rails, seatpost, quick release, or even the spoke crossings. The frame acts as a sound box that carries noise a long way, so where you hear the sound and where it actually comes from are often two different places.

The trick to finding a noise is process of elimination. If it disappears when you stand up out of the saddle and pedal, the saddle and seatpost are the prime suspects. If it goes away when you switch to different pedals or regular shoes, it's a pedal or cleat problem. If you feel play when rocking the cranks side to side, or the cranks feel rough and gritty when turned by hand, suspect the BB bearings. Many creaks disappear simply by loosening the part, cleaning it, applying a thin layer of grease (carbon assembly paste for carbon parts) and retightening it to the specified torque.

How long do wear parts last?

The chart below shows typical replacement intervals for the main wear parts in distance ridden. The start and end of each bar mark the range within which you'll 'usually end up replacing it'. Riders on clean roads who look after their chains will see the right-hand end; those who often ride in rain or on dirt, or who skimp on maintenance, will see the left-hand end or even less. Cassette and chainring life in particular depends heavily on whether you replace the chain on time.

Maintenance planner

Even if you know the 'what to do every so many km' guidelines, translating them into a calendar based on how much you ride is surprisingly tedious. Enter your average weekly distance and typical riding conditions in the planner below, and it shows at a glance roughly how many weeks apart each maintenance task falls and what the year's schedule looks like. The more you ride in rain or on dirt, the more abrasive grime builds up and the shorter the intervals. Items that degrade with time regardless of distance, such as cables and overhauls, are capped at a maximum interval of one year.

DIY vs. shop: comparing repair costs

The biggest benefit of doing your own maintenance is less about cost than understanding. When you know the state of your bike, problems on the road won't throw you, and when you do take it to a shop you can describe the symptoms precisely. That doesn't mean doing everything yourself always pays. For jobs that need expensive special tools, like a truing stand or bleed kit, paying a shop a few times costs less than the tools, and a job a skilled mechanic finishes in 30 minutes can take a first-timer half a day. The table below shows approximate ranges based on typical shops in Korea, and prices can vary widely by region, shop and component grade.

The table shows that the more often a job comes around — fixing flats, chain care, pad replacement — the more you gain by doing it yourself. Conversely, for infrequent jobs with expensive tools, like bleeding or BB replacement, using a shop often makes more sense. For most riders, the most economical approach is a 'hybrid' one: find a good local shop, do the simple jobs yourself and hand over the big ones. A full overhaul once a year, with a professional checking everything down to frame cracks and hub bearing condition, is also a good investment.

FAQ