Troubleshooting by Symptom

When something feels wrong on the bike, start here. This index lists the most common symptoms cyclists actually describe — “my chain skips”, “the brakes squeal”, “there’s a creak” — and walks you through the likely causes in order of probability. Try fixes from the top down; cheaper and faster checks come first.

A.1 Drivetrain symptoms #

”Chain skips under power on certain gears” #

Most common cause first.

1. Worn chain stretching past wear limit → measure chain (3.1). A chain at 0.5%+ skips on cogs that have worn to match the old chain. Replace chain; cassette may follow.
2. Bent derailleur hanger → check alignment (3.16). Even a 2 mm deviation makes some gears unindexable. Single most underdiagnosed cause.
3. Cable tension out of spec → re-index rear derailleur (3.15 step 7+).
4. Worn jockey wheels → derailleur cage pulleys eventually develop sharp teeth. Replace as a pair.
5. Worn cassette only on a few cogs → if you ride mostly in 2–3 gears, those wear faster. Visible “shark fin” tooth shape confirms.

”Chain drops off the chainring(s)” #

1. Front derailleur limits set wrong → reset H/L limits (3.14).
2. Worn chainring teeth (especially small ring on 2x setups) → visible tooth wear; replace ring.
3. Stretched chain (1x setups: chain that’s too long jumps off in rough terrain) → measure (3.1) and re-size.
4. Missing/worn chain retention → narrow-wide chainring teeth wear smooth on 1x; consider chain guide.

”Grinding or rough feeling when pedaling” #

1. Dirty drivetrain → drivetrain deep clean (12.3).
2. Dry chain → lubricate (12.4).
3. Worn chain rolling on worn cassette → measure chain; replace as a set if needed.
4. Damaged BB bearings → with the chain off the front ring, spin the cranks; should be silky and silent. Grinding/notching = BB needs replacement (3.12/3.13).
5. Crank arm loose → check pinch bolts (Hollowtech) or torque cap (5–7 Nm preload, then bolts to spec).

”Clicking once per pedal stroke” #

This always indicates a torque-loaded interface.

1. Loose chainring bolts → torque to spec (typically 8–10 Nm; check spec).
2. Loose pedal → re-grease and torque (35 Nm typical). Both pedals.
3. Loose crank arm → check Hollowtech pinch bolts, or square taper bolt.
4. Cleat loose on shoe → check cleat bolts on both shoes.
5. Saddle rail clamp loose → check seatpost head bolts.

”Shifting feels sluggish or imprecise but no skipping” #

1. Cable contamination/corrosion → especially after winter. Replace cable and housing (3.17).
2. Cable end frayed inside housing → visible at pinch bolt; replace cable.
3. Crushed housing end → cut a fresh end with proper cable cutter.
4. Worn shifter mechanism (mechanical only) → replace shifter unit.

A.2 Brake symptoms #

”Brakes squeal” #

1. Pad contamination (degreaser, sealant, finger oil, chain lube overspray) → clean rotor with isopropyl alcohol; if pads are contaminated, replace them. Once contaminated, pads usually can’t be saved.
2. Glazed pads → light sand on fine sandpaper, re-bed (4.2). New pads also need bedding.
3. Toed-in incorrectly (rim brakes) → set up so the front of the pad contacts the rim 1 mm before the rear.
4. Loose caliper mounting bolts → re-align caliper (4.7), torque to spec.
5. Bent rotor causing intermittent contact → true rotor (4.3).

”Brake lever feels spongy / pulls to the bar” #

1. Air in hydraulic system → bleed the brake (4.4 Shimano / 4.5 SRAM).
2. Worn pads → measure pad thickness; replace at or below 1 mm as a conservative app threshold, or earlier/later according to the brake manufacturer’s stated minimum (4.1).
3. Pistons sticking → push pistons back, clean exposed area with isopropyl, work them in/out by lever pumping with the pad spreader in.
4. Master cylinder seal failure (rare) → lever rebuild kit or replacement.

”Brakes drag / rub” #

1. Caliper not centered over rotor → align (4.7).
2. Bent rotor → true (4.3).
3. Pads stuck out (after fitting new pads without pushing pistons fully back) → remove pads, push pistons back with pad spreader, refit.
4. Wheel not seated in dropouts → loosen axle, settle wheel, re-torque.
5. Loose hub bearings allowing wheel to wobble laterally → check hub adjustment.

”Lever pulls to the bar — no braking” #

Stop riding immediately. Walk the bike home.

1. Hose has leaked dry → check for fluid trace anywhere on the hose, lever, or caliper. Repair source, then bleed.
2. Pad fully worn through to backing plate → caliper now pushes piston past the seal; needs rebuild. Replace pads first; re-bleed.
3. Total cable failure (mechanical brakes) → replace cable.

”Pulsing through the lever” #

1. Bent rotor → true (4.3).
2. Heat-warped rotor (after a long descent) → cools down, may stay warped; true or replace.
3. Inconsistent pad transfer (uneven black film on rotor) → re-bed (4.2) after cleaning rotor.

A.3 Wheel & tire symptoms #

”Slow leak / tire goes flat overnight” #

1. Small puncture → on tubeless: top up sealant (5.5), spin to redistribute, often self-heals. On tubed: find leak by listening or submerging tube (5.3).
2. Valve core loose → tighten with valve core tool. Common on tubeless setups.
3. Bead seating slightly off (tubeless) → unseat, clean bead, re-seat with proper inflator.
4. Rim tape failure (tubeless) → leaks past spoke holes; re-tape rim (5.4 prep stage).
5. Pinhole in tube at the seam → replace tube.

”Wheel wobbles side to side” #

1. Out of true → lateral truing (5.7).
2. Loose hub bearings → cone wrench adjustment (5.10) or cartridge bearing replacement (5.11).
3. Loose axle / quick release → snug to spec.
4. Cracked rim or bent spokes → inspect closely; severely damaged wheels should be retired.

”Wheel hops up and down” #

1. Out of round (radial truing needed) → radial truing (5.8).
2. Tire mounted unevenly → deflate, work tire bead around the rim, re-inflate.
3. Damaged rim (dent from impact) → may not be repairable; rim or wheel replacement.

”Tubeless tire won’t hold pressure even after sealant” #

1. Bead not seated properly → unseat tire, clean bead and rim seat, use proper inflator (5.4).
2. Tape damaged (especially after recent tire swaps) → re-tape (5.4 prep).
3. Major sidewall cut → plug (5.6) or new tire.
4. Sealant dried out → too old; clean out and replace (5.5).

A.4 Suspension symptoms #

”Fork dives too much under braking / feels harsh on small bumps” #

1. Wrong sag setting → measure and adjust (8.1). Most common cause.
2. Compression damping wrong → start at manufacturer’s middle setting, adjust 2 clicks at a time.
3. Stiction from dirty seals → at minimum wipe stanchions clean before each ride; if persistent, lower leg service (8.2).
4. Wrong air pressure for rider weight → start from manufacturer’s chart for your weight, then sag-tune.

”Suspension feels notchy or sticks” #

1. Dirty stanchions / dust seals → clean and lubricate stanchions; consider lower leg service (8.2).
2. Old oil / dry foam rings → lower leg service (8.2).
3. Damaged stanchion coating → if you see scratches in the anodizing, the fork needs servicing professionally.

”Loud clunk when fork bottoms out” #

1. Insufficient air pressure → increase 5–10 PSI per iteration.
2. No bottom-out token / volume spacer → add one (air spring service 8.3).
3. Damper failure → if changes to air pressure don’t help, damper may need professional rebuild.

”Sag set correctly but ride still harsh” #

1. Rebound too fast → slow it 2 clicks and re-test.
2. Compression too firm → open compression damping.
3. Tire pressure too high → lower tire PSI before chasing suspension settings.

A.5 Steering & cockpit symptoms #

”Knocking / clunking from front end over bumps” #

1. Loose headset preload → tighten top cap until no play, then secure stem (6.1 step 5).
2. Worn headset bearings → replace bearings (6.3).
3. Loose stem clamp on the steerer → torque to spec.
4. Cracked headset cup or frame → inspect carefully; serious if confirmed.

”Headset feels notchy / catches at certain steering angles” #

1. Indexed bearings (worn from impact loading) → bearing replacement (6.3).
2. Contamination / rust in bearings → new bearings.
3. Misaligned crown race → re-seat (6.4).

”Bars or stem creak” #

1. Dry interface between bar and stem → degrease, apply carbon paste (carbon) or light grease (alu), re-torque.
2. Stem clamp bolts unevenly torqued → loosen all, retorque in criss-cross pattern.
3. Steerer-stem interface dry → strip, clean, light grease (NOT on carbon steerer — paste only).

A.6 Generalized creaks (the most frustrating diagnostic) #

When you can’t tell where a creak comes from, work this list. Creaks are vibrations transmitted through the frame, so the source can feel like it’s somewhere it isn’t.

1. Pedal threads (most common; both sides) → remove, grease, retorque to spec.
2. Cleat bolts → remove, grease, retorque (loose cleats sound like BB creaks).
3. Saddle rails in clamp → loosen, regrease rails, retorque.
4. Seatpost in frame → remove, clean, apply correct paste/grease, reinsert.
5. Crank arm to spindle interface → check Hollowtech pinch bolt torque; on creak, remove crank, clean and grease spline, reinstall.
6. Chainring bolts → torque to spec.
7. BB to frame → remove, clean, install with anti-seize (threaded) or fresh press (press-fit).
8. Quick release / through-axle → clean, light grease on the threads.
9. Rear shock mounting hardware (full-suspension) → check pivot bolts.
10. Headset (rare creak source but possible) → strip and regrease.

A useful diagnostic trick: try to reproduce the creak while standing stationary, by torquing pedals against the brakes. If it persists, it’s drivetrain or BB-related. If it only happens while seated and pedaling, it’s saddle or seatpost.

A.7 Drivetrain noise, not skipping #

”Chain rattle” #

1. Chain too long → check sizing (3.5).
2. Worn jockey wheels → replace.
3. Insufficient B-tension → adjust (3.15 step 5).

”Grinding when pedaling backwards” #

1. B-tension too tight → loosen by 1/4 turn at a time.
2. Chain too short for the cog selection → re-size.

”Chain slap on chainstay” #

1. Worn or missing chainstay protector → replace neoprene/rubber protector.
2. Chain too long → re-size.
3. Clutch derailleur disengaged (if you have a clutch RD) → check clutch lever / button position.