AI quick summary
- Check the frame first and hardest: cracks (especially around the head tube, bottom bracket, and chainstays), repairs, and crash damage. A damaged frame is a dealbreaker; everything else is negotiable
- Wear items tell you how the bike was treated: chain stretch (a $10 checker), brake pad wear, tire condition, and cassette wear. Replacing a full drivetrain + brakes + tires can cost $400–800 — factor it into the price
- Test ride: shift through all gears, brake hard (front and rear), stand and sprint (feel for flex), and listen for creaks. Creaks indicate loose bearings or frame issues
- Verify the serial number (against bike registries for theft) and check the title. A deal too good to be true often is — stolen bikes move fast
/ 01
The frame — the dealbreaker
Start with the frame. A frame with a crack, a repair, or significant crash damage is a dealbreaker — everything else on the bike is replaceable, but the frame is the bike. Inspect carefully, especially on carbon frames.
Carbon frame red flags: visible cracks or splits in the paint (which can indicate underlying carbon damage), soft spots or flex when pressing firmly on the tubes (delamination), repaired areas (a section that looks different — sanded, repainted, or bulging), and impact marks (star cracks from rock strikes or crashes). Tap the frame with a coin: a clear ring is healthy carbon; a dull thud suggests delamination or a crack beneath the surface.
Alloy frame red flags: dents (especially on the top tube and down tube — from handlebar rotation in a crash), cracks at the welds (look closely at every weld junction), and bent derailleur hangers (a sign of a crash or poor transport). A bent hanger is replaceable; bent frame tubes are not.
/ 02
Drivetrain and brake wear
Wear items that indicate how the bike was treated — and what you'll pay to replace.
| Item | How to check | Replacement cost | Dealbreaker? |
|---|---|---|---|
| Chain | Chain checker tool (0.5% = OK, 0.75%+ = worn) | $30–50 (chain); $150+ if cassette also worn | No, but negotiate price down |
| Cassette | Hooked/pointed teeth = worn; skips under load | $90–150 | No, but factor cost |
| Brake pads | Look at pad thickness; grooves gone = worn | $25–40/pair (road); more for disc pads | No |
| Tires | Tread worn flat, cuts, sidewall cracks | $40–80/tire | No |
| Cables/housing | Fraying, rust, sluggish shifting | $30–60 full replacement | No |
| Bearings (hub, BB, headset) | Feel for notchiness/play when wiggling wheels/cranks/bars | $20–50/part + labor | No, but adds up |
/ 03
The test ride
Always test ride. Static inspection misses things you'll only feel in motion. Shift through every gear (front and rear) — smooth, crisp shifts mean a healthy drivetrain; skipping, ghost-shifting, or hesitation indicate wear or misadjustment. Brake firmly from speed (both front and rear separately) — sponginess indicates air in hydraulic lines or worn cables.
Stand and sprint: feel for flex in the bottom bracket and frame. Listen for creaks — a creaking bottom bracket, headset, or seatpost indicates loose or worn bearings (fixable) but also suggests the bike wasn't well-maintained. Check the steering: lift the front wheel and turn the bars — a notchy or stiff headset indicates worn bearings.
If the seller won't let you test ride (some don't, for insurance reasons), that's a red flag. A legitimate seller wants you to verify the bike works.
/ 04
Title and theft check
Verify the serial number. It's usually stamped on the underside of the bottom bracket shell. Check it against bike registries (Project 529, Bike Index) — if the bike is listed as stolen, walk away and report it. Ask the seller for proof of purchase (a receipt or original order) — legitimate owners can usually produce one.
A price too good to be true usually is. A $4,000 bike listed for $1,200 with no story is almost certainly stolen. Stolen bikes move fast and are often resold across regions. Use your judgment: if the seller is evasive about provenance, can't describe the bike's history, or wants cash only with no record, those are theft indicators.
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