Buying a used bike: the ten-minute inspection

A used road bike is often the best value on the market, and buying one is not difficult if you look at the right things in the right order. Ten minutes, a small torch and a willingness to walk away are all you need. This is the inspection we would do ourselves, in the order that finds the deal-breakers first, so you do not spend eight minutes admiring the shifting before noticing the crack under the down tube. It is written for a road bike but nearly all of it applies to gravel and hybrid bikes too.

Before you go: the paperwork

Bicycle theft is common enough that a used-bike inspection starts before you see the bike. Van Lierop and colleagues' study of theft in Montreal found that roughly half of the cyclists surveyed had had a bike stolen at some point, and that most thefts went unreported and unrecovered — which is another way of saying that a stolen bike is likely to be resold. Ask for the frame number (stamped under the bottom bracket, where the cranks meet the frame) and the original receipt or a photo of it. A seller who cannot provide a frame number, or does not know where to find one, is not necessarily a thief, but a seller who refuses to is telling you something. Check the number against whatever register your country's police support before money changes hands. Being rushed is the other signal: a genuine seller lets you take your time.

Minute one to three: the frame

This is where the deal-breakers live, so do it first and do it with the bike clean — ask the seller to wash it, or bring a rag. Run a torch along every tube at a low angle and look for cracks, ripples, bulges and paint that has flaked in a line rather than a chip.

• Aluminium and steel. Cracks show up at welds and at the ends of tubes: the head tube junctions, the bottom bracket shell, the chainstays where they meet the dropouts. A study of steel-frame fatigue against the ISO 4210 test protocol found that the stress concentrations were at exactly these joints, which is why the standard's fatigue tests load them. A dent in a steel tube is usually cosmetic; a dent in an aluminium tube is a reason to walk away, because aluminium does not tolerate being reshaped.
• Carbon. Here is the honest bit. Impact damage to carbon composite tubes can be invisible from outside: research using phased-array ultrasound on carbon bicycle tubes found sub-surface delamination from impacts that left little or no surface mark. Tap along the tubes with a coin — a clear tick is good, a dull thud where the rest ticks is not — and press firmly with your thumb looking for soft spots. Look hard at the top tube (bars swinging round in a crash), the down tube behind the head tube (front-end impacts), the seat tube around the clamp (over-tightening) and the chainstay near the crank (chain drops). If a carbon frame has been crashed, the only way to be sure is a shop with a scanner, and for an expensive frame that is worth paying for.
• Alignment. Stand behind the bike, sight along the rear wheel to the front. The wheels should sit in one plane. Then look from the front at whether the fork blades are symmetrical and whether the head tube paint shows the ripples that a front impact leaves. A bent fork or rear triangle is a walk-away.

Minute four: wheels

Lift each end and spin. Watch the gap between rim and brake pad, or rim and frame on a disc bike: a wobble of a couple of millimetres is trueable, a hop or a flat spot is not. Pluck the spokes on each side — they should ring at a similar pitch, and a dead one is loose or broken. With rim brakes, run a fingernail across the braking surface: a deep concave groove means the rim is near the end of its life, and a rim is a large fraction of a wheel's price. On a disc bike, check the rotor is not blued or warped and that the pads have material left. Rock the wheel side to side in the frame: play at the hub is a bearing job. Look at the tyres last; tyres are cheap and a seller who has left bald tyres on is telling you how the rest was maintained.

Minute five to six: drivetrain

Chain wear is the tell for the whole transmission, because a worn chain wears the cassette and chainrings to match, and a new chain on worn sprockets skips under load. Bring a chain checker; they cost a few euros and most shops will lend one. Anything past the 0.75 per cent mark means a new chain, and past 1 per cent almost certainly means cassette and probably chainrings too, which together can be a meaningful fraction of the bike's price. Without a checker, look at the chainring teeth: healthy ones are symmetrical, worn ones lean into a shark-fin shape. Spicer and colleagues' laboratory work on chain-drive efficiency is a reminder of why this matters beyond cost — a clean, well-aligned chain transmits power at high efficiency, while a worn or badly lubricated one loses a few per cent, which you feel as a bike that seems inexplicably slow.

Then shift through every gear, front and rear, while turning the cranks. Hesitation on one or two sprockets is cable stretch; hesitation everywhere is a bent derailleur hanger or a worn cassette. Grab the crank arms and push them sideways towards the frame: play here is the bottom bracket, which ranges from a cheap fix to an awkward one depending on the standard. Look at the derailleur cage for scrapes and check the hanger is straight by eye from behind.

Minute seven: brakes and bearings

Squeeze each lever. It should firm up well before the bar. A lever that comes to the bar on a hydraulic disc bike needs a bleed; on a rim-brake bike it is pads or cables. Check the pads for life and the cables for fraying at the lever and where they enter the frame. Then the headset: hold the front brake, rock the bike forwards and back, and feel for a knock at the head tube. Lift the front wheel and turn the bars slowly — notchiness means pitted bearings. Finally the saddle and post: pull the post out and look for corrosion or a stuck post, which on an aluminium-in-carbon or carbon-in-aluminium combination can be genuinely stuck.

Minute eight to nine: ride it

Even round a car park. Listen for creaks under load (bottom bracket, seatpost, headset), feel for a shimmy when you take one hand off, brake hard once from moderate speed, and shift under a bit of pressure on a slight rise. A bike that is quiet, tracks straight and stops without pulling to one side has passed the checks that matter. A bike that creaks is not necessarily broken, but you are now negotiating.

Minute ten: the size question

None of the above matters if the frame is the wrong size, and used bikes are where people compromise on size because the price is good. Do not. A used bike one size too big is a permanent problem; a good deal on the wrong frame is not a good deal. Our bike-fit basics post has the numbers to check on the spot.

Recalls and regulation

Two things a private sale does not protect you from. A new bike sold in the UK must meet the Pedal Bicycles (Safety) Regulations, which reference the ISO 4210 standard; a used one is sold as seen, so the responsibility for checking is yours. And components are recalled more often than people think — forks, stems, cranks and disc rotors have all been the subject of alerts. The UK's product-safety register is searchable by product, the EU's Safety Gate is the equivalent, and a ten-second search for the frame or fork model before buying is cheap insurance.

What to budget on top

In our experience a fair used bike needs roughly a chain, cables or a brake bleed, bar tape and tyres within the first few months, and a full service is worth doing regardless of what the seller says. Price that in. What you get in return is usually a bike from one or two tiers above what the same money buys new — which, as long as the frame is sound and the size is right, is the point. Then wash it properly, decide on wax or lube, and start the maintenance schedule from day one so the next owner has an easier inspection than you did.