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Items19
1
Run the Serial Number Through a Stolen Bike Register
Do this first, because no mechanical bargain survives the discovery that the bike is stolen. Most serial numbers are engraved under the bottom bracket, so turn the bike over and photograph it. Bike Index is a free nonprofit register, and its search also shows registered bikes with similar serials, which helps when a digit has been misread or deliberately altered.
A serial that has been filed off, painted over or doesn't match the paperwork is a reason to leave. A clean result only means nobody reported the bike missing; it doesn't prove the seller owns it.
2
Ask for Proof of Ownership and a Daylight Viewing
A receipt, service records or the original owner's paperwork make a story harder to fake, and an honest seller rarely minds being asked. Arrange to see the bike in daylight with time for a short ride, because dim garages and evening parking lots hide cracks, rust and a tired drivetrain.
A seller who won't allow a proper inspection, show proof of ownership or let you ride the bike is telling you something. So is a price far below what the same model fetches elsewhere: if it seems too good to be true, it usually is.
3
Inspect the Frame for Cracks, Dents and Deep Rust
Frame damage is the one fault that can make a bike worthless, so give the frame the most time. Work around it in good light, with a flashlight for the shadows, paying closest attention to the head tube, the bottom bracket, the seat stays and every weld. Paint that has bubbled, lifted or cracked in a line deserves a close look, because paint cracks often follow a crack in the frame underneath.
Aluminum tends to crack rather than bend, and the cracks can be very fine. On a steel frame, treat rust that goes deeper than the paint as a reason for a closer look or a workshop's opinion. A crack anywhere, or a dent in a frame tube, is a reason to walk away, whatever the components are worth.
4
Check Carbon Frames and Forks for Hidden Damage
Carbon fails differently from metal: an impact can leave damage below the surface that the eye can't see. Look closely at the top and down tubes, where car and roof rack clamps can crush carbon, and at the seatpost clamp slot, where a small crack can turn and run horizontally around the tube.
Lift the bike a few inches and let it drop, listening for rattles or clunks from inside the frame or fork. Tap suspect areas gently with a coin and listen for a change in sound. For an expensive carbon bike, or whenever you're unsure, a carbon repair specialist can check the frame with ultrasound before you pay.
5
Sight Down the Rear Derailleur Hanger
Stand behind the bike and look along the rear derailleur. The cage should hang vertical and parallel to the cogs; if it leans in toward the spokes, the hanger is probably bent. Hangers are designed to bend easily, so a crash or a fall on the drive side often shows up here first.
A bent hanger can usually be realigned or replaced, unless it is built into the frame. The real question is what else took the hit. Check whether the derailleur itself is twisted, and look for scrapes or gouges on the bar ends and brake hoods, which suggest the bike has been crashed.
6
Measure the Chain with a Chain Checker
A chain elongates as its pins and rollers wear, and a worn chain quietly grinds down the cassette and chainrings with it. A go/no-go gauge such as Park Tool's CC-3.2 drops into the links in seconds and settles the question without guesswork.
On 5- to 10-speed drivetrains, replace the chain at or just before 0.75% wear; on 11- and 12-speed, at or just before 0.5%. A chain at the limit is a cheap fix. A chain well past it often means a new cassette too, so price that into your offer. SRAM Flattop and T-Type 12-speed chains need a different gauge.
7
Look at the Cassette and Chainring Teeth
Worn teeth confirm what the chain checker suggests. Healthy teeth are evenly shaped; worn ones turn hooked and pointed into a shark-fin profile as the chain eats into one face. Check the cogs that get ridden most, and the chainring teeth all the way around.
Watch for a shiny new chain running over hooked teeth. It can mean the seller replaced the cheap part and left you the expensive one, and a new chain on badly worn sprockets is likely to skip, especially on the smaller cogs, which hard pedaling on the test ride will reveal.
8
Spin Each Wheel for True and Smooth Bearings
Lift each end of the bike and spin the wheel, watching the rim pass a brake pad or the frame. A slight side-to-side wobble can be trued by a shop for little money; a big buckle or a flat spot points to a bent rim and possibly a new wheel.
Feel and listen while it spins, too. The hub should turn quietly and freely, with no grinding or rough patches. Squeeze neighboring pairs of spokes as you go around: one that feels slack, or one that is missing altogether, explains a wheel that won't stay straight.
9
Rock the Wheels for Hub Play
Hold the top of each tire and push it firmly side to side against the frame or fork. Obvious movement means the hub bearings are loose or worn. Some hubs simply need adjusting, but if the bearing surfaces are damaged the honest answer may be a replacement wheel, which changes what the bike is worth to you.
Check that the wheel is properly clamped before you judge it, since a loose quick-release lever or thru-axle feels much like bearing play.
10
Check Rims and Disc Rotors for Brake Wear
Braking slowly wears away metal, and on rim brakes that metal is part of the wheel. Lay a straight edge across each rim's braking surface: if the track is obviously concave, curved inward, the rim is worn out and the wheel needs replacing.
On disc brakes, measure each rotor where the pads touch it, with calipers if you have them. Shimano rotors start at 1.8 mm and should be replaced at 1.5 mm, a limit stamped on the rotor itself; most SRAM rotors are retired at 1.55 mm. Rotors are a modest expense, but worn rims mean new wheels, which can wipe out the saving on a cheap bike.
11
Squeeze the Brake Levers Hard
Pull each lever as hard as you would in an emergency. It should firm up well before it reaches the handlebar and stay firm while you hold it. A spongy lever points to worn cables or air in a hydraulic system, and both add to your running costs.
While you're there, look at pad thickness and check that cables aren't frayed where they enter the lever or the brake. Thin pads are a cheap swap and a fair bargaining point. Save the final verdict for the test ride, where a firm stop from speed shows whether the brakes bite evenly.
12
Test the Headset with the Front Brake On
Hold the front brake, rest your other hand around the top of the head tube and rock the bike forward and back. A knock you can feel through your hand means a loose or worn headset.
Then lift the front wheel off the ground and turn the bars slowly from lock to lock. They should swing smoothly. If the steering seems to lock or center itself in the straight-ahead position, the lower bearing races are likely dented, and the usual fix is a new headset. A loose headset is often only an adjustment, while a dented one means parts and labor, so it is a fair point to raise on price rather than a reason to walk away.
13
Wiggle the Cranks for Bottom Bracket Play
Grab a crank arm near the pedal and push it firmly toward and away from the frame. There should be no movement at all; any play points to worn or loose bottom bracket bearings, or a crank that has worked loose. Then spin the cranks backward by hand and feel for grinding or roughness.
A worn bottom bracket is normally a workshop job rather than a reason to walk away, so treat it as a reasonable thing to negotiate on and let the shop check the frame's shell while the bearings are out.
14
Make Sure the Seatpost Moves
Ask the seller if you can open the seat clamp, then slide the post up and down. It is a thirty-second check that rules out one of the nastiest surprises in used bikes. A seatpost seized into the frame can take a lot of work to free, and the attempt can ruin the frame. If it won't budge, don't buy the bike, however tempting the rest of it is.
A post that moves also lets you set the saddle at your own height for the test ride, which makes everything that follows more meaningful.
15
Inspect the Suspension Fork Stanchions and Seals
The shiny upper tubes of a suspension fork, the stanchions, should be smooth, with no pitting or scratches, because damage there keeps the fork from working properly. Scratches on the lower legs are only cosmetic.
Look for oil traces running down from the seals. Then pump the fork several times and look again, in case the oil was simply wiped off before you arrived. A leaking seal means a service is due. Ask how often the fork has been serviced and for receipts for any claimed rebuild; a fork with a clean record and smooth stanchions is worth paying a little more for.
16
Check the Rear Shock and Pivot Bearings
On a full-suspension bike, look along the rear shock's shaft for oil. Air shocks show leaks plainly; on a coil shock you have to look closely behind the spring.
Then grip the rear of the swingarm and try to move it side to side. There should be very little movement. Noticeable play points to worn pivot bearings, which are fixable but add up quickly on a frame with several pivots. Push down hard on the saddle a few times as well: the rear should compress and return smoothly, without knocks or creaks that a seller would rather you didn't hear.
17
Pump Up the Tires and Check the Sidewalls
Tires are a smaller cost, but they tell you how the bike has been kept. Inflate them and see whether they hold air, then check the tread and both sidewalls all the way around.
Look hardest at the section that sat on the ground if the bike was stored flat. Perished rubber or cracks in the sidewall mean budgeting for new tires before you ride far. A bike left on flat tires for months has often been neglected in other ways, so let it sharpen your attention on the bearings and the chain.
18
Get an E-Bike's Battery and Motor Checked by a Dealer
On an e-bike, the battery is the part that can sink the deal: replacing it could cost 20 to 50% of the purchase price or more. A certified dealer for the motor brand can read the system before you buy. For a Bosch bike, the diagnostic report includes the number of charging cycles and an estimate of battery capacity.
If the seller won't allow that, ride far enough to get a sense of how the battery currently performs. Remember too that e-bike warranties generally don't transfer to a second owner, so the seller's remaining cover is usually worth nothing to you.
19
Ride It Through Every Gear
The test ride ties every other check together. Shift across the whole range, front and rear, first gently and then under load. Chain skipping or noisy, hesitant shifts point back to a worn drivetrain or a bent hanger.
Brake firmly from speed and feel for an even, confident bite. Listen for clicks, creaks and clunks from the frame and bottom bracket, and make sure the size and steering suit you. If you aren't happy, don't feel obligated to buy. A seller who refuses a test ride altogether has given you your answer.
