Inspecting a used single-speed bike takes about fifteen minutes and follows a fixed order: frame first, then wheels, drivetrain, brakes, and finally fit. Check the frame for cracks and alignment before anything else, because a bent or cracked frame is the one fault that makes the bike worthless — everything else is a replaceable part with a known price. A single-speed is a bike with one gear ratio and no derailleurs.
Some are freewheel bikes that coast; some are fixed-gear ("fixie") bikes where the rear cog is locked to the hub, so the pedals turn whenever the wheel does. Many track-style frames sold as single-speeds have flip-flop hubs that accept either. Knowing which one you are looking at changes how you test the drivetrain and how much braking matters.
Table of Contents
- Start With the Frame, Because Nothing Else Matters If It Fails
- Wheels, Tyres, and the Parts People Forget to Look At
- Drivetrain — Chain Line, Chain Wear, and Whether It Is Fixed or Free
- Brakes, Including What a Fixed Gear Legally and Practically Needs
- Fit, and the Test Ride That Confirms It
- Pricing the Faults You Found
- Frequently Asked Questions
Start With the Frame, Because Nothing Else Matters If It Fails
Run your fingers along the top and bottom of the down tube behind the head tube. That area takes the load in a front impact, and steel frames often wrinkle there while aluminium and carbon crack. Look for paint that has cracked in a line rather than chipped in a patch — a crack in paint over a tube seam frequently means a crack underneath. Check alignment by standing behind the bike and sighting down from the saddle to the front tyre. The wheels should sit in one plane.
Then look at the rear dropouts, the slots the rear axle sits in: on a single-speed they are usually horizontal or track-style so the wheel can slide back to tension the chain. Both dropouts should look identical and undamaged, and the axle should sit at roughly the same depth on each side when the wheel is straight. Steel frames rust from the inside. Pull the seatpost out and look and smell inside the seat tube. Surface rust is normal on an older steel bike; flaking, scaly rust or brown water is not. On any frame, check the head tube for play by squeezing the front brake, rocking the bike forward, and feeling for a knock at the headset — that is usually a cheap bearing fix, but a notchy, indexed feel when you turn the bars slowly means the bearings have dented their races.
Wheels, Tyres, and the Parts People Forget to Look At
Lift each wheel and spin it. Watch the gap between the rim and the brake pad, or between the rim and a fixed point like the chainstay if there are no brakes. Side-to-side wobble over about two or three millimetres means the wheel needs truing, which is inexpensive; a visible flat spot or a bend you can see from above usually means the rim is finished. Squeeze pairs of spokes around each wheel. They should all feel similar and firm.
Several loose spokes on one side, or a spoke you can turn by hand, means the wheel has lost tension and may have been ridden that way — which often means the rim is already deformed. Check for broken or replaced spokes near the rear hub in particular. Look at the rim braking surface if the bike uses rim brakes. Many rims have a wear indicator: a groove or a small dimple machined into the sidewall. When the groove disappears, the rim is worn through its safe thickness and must be replaced, no matter how good the rest of the bike looks. Finally, grab each wheel at the top and rock it side to side against the frame — play here is hub bearing wear, which is adjustable on cup-and-cone hubs and a replacement on sealed ones.
- Tyres cracked in the sidewall or squared off in the centre: budget for a replacement pair.
- Rust on the spoke nipples or inside the rim well: the wheel has lived outdoors.
- A wheel that will not sit straight in the dropouts: check the axle before blaming the frame.
Drivetrain — Chain Line, Chain Wear, and Whether It Is Fixed or Free
On a single-speed the chain runs in one line from chainring to cog with no derailleur to absorb error, so the chain line matters more than on a geared bike. Crouch behind the bike and look along the chain. It should run dead straight; if it angles inward or outward, the cog or chainring is spaced wrong, and the chain will drop under load. Ask whether spacers have been changed. Test chain tension by pushing the chain up and down midway between the sprockets. Around a centimetre of total movement is normal. Then rotate the cranks slowly through a full turn and watch the tension. If it goes tight and slack in a cycle, the chainring is not perfectly round or the crank is bent — annoying on a freewheel bike, genuinely unpleasant on a fixed gear, where a tight spot fights your legs.
Check tooth shape on the chainring and cog. Healthy teeth are symmetrical; worn teeth hook backwards like a breaking wave. A stretched chain wears sprockets, so if the chain looks old, assume you are buying a chain, a cog, and possibly a chainring together. Also grab a crank arm and pull it sideways — movement means a loose crank bolt or a worn bottom bracket. To tell fixed from free, lift the rear wheel and turn it backwards. If the pedals turn backwards with it, the bike is fixed. If the wheel spins with a ticking sound and the pedals stay still, it is a freewheel. On a flip-flop hub, look at both sides of the rear hub: a fixed side has a smaller lockring threaded outside the cog, which stops the cog unthreading when you slow down with your legs.
Brakes, Including What a Fixed Gear Legally and Practically Needs
Squeeze each lever. It should stop firmly well before it touches the handlebar, and the pads should hit the rim squarely, not the tyre and not the air below the rim. Pads with the grooves worn away, or pads hardened and shiny with embedded grit, need replacing — a cheap fix, but factor it in. Check the cables where they enter the levers and the callipers. Frayed strands, kinked housing, or orange rust inside the housing all mean the brake will feel vague no matter how good the pads are.
On disc brakes, look for a rotor that is scored, blued from heat, or visibly warped, and check the pad thickness through the calliper slot. Fixed-gear bikes are sometimes sold with no brakes at all. Slowing a fixed gear with leg resistance works, but it is weaker than a front brake and depends on your legs staying attached to the pedals, which is why riders use toe clips or clipless pedals. Many jurisdictions require at least one working brake on a bike ridden on public roads, so check your local rules before buying a brakeless bike, and budget for a front brake and lever if the frame has the mounting hole drilled in the fork crown. A fork with no brake hole cannot take a standard calliper.
Fit, and the Test Ride That Confirms It
Straddle the bike with both feet flat. On a road-style single-speed you want roughly two to five centimetres of clearance between the top tube and your body; less than that and the frame is too big, and no amount of adjustment fixes a frame that is too big. Too small is more workable — a longer seatpost and stem buy some room — but the handling will feel cramped. Check that the seatpost can reach your leg length without passing its minimum-insertion mark, the line etched near the bottom.
If the post is already at that line and your knee is still bent hard at the bottom of the stroke, the frame is too small for you. Sit on the saddle and look at the bars: your reach should feel comfortable without locked elbows or a rounded lower back. Then ride it, ideally on a quiet street rather than a car park. Listen for a click once per pedal revolution, which usually points at the bottom bracket or a crank; a rhythmic rubbing, which points at a brake or a bent rim; and a chain that skips under hard pedalling, which means a worn cog and chain. On a fixed gear, ride slowly at first and remember you cannot coast.
- Bring a multi-tool so you can adjust saddle height before the ride.
- Ride with your hands off the bars briefly on a safe, empty stretch — a bike that veers hard to one side may have a misaligned frame or fork.
- Stand up and pedal hard in a straight line: this loads the frame and drivetrain in a way that rolling along does not.
Pricing the Faults You Found
Separate what you found into three groups. Consumables — chain, cog, cables, pads, tyres, bar tape — are cheap and expected on a used bike; treat them as a discount you can name, not a reason to walk away. Service items — headset bearings, bottom bracket, wheel truing — cost more and may need a shop if you do not own the tools. The third group ends the negotiation.
A cracked or dented frame, a bent fork, a rim worn past its indicator on a bike with rim brakes, or a frame with damaged dropouts that will not hold the wheel straight are all reasons to stop. On cheap single-speeds, the cost of fixing any one of these often exceeds what the whole bike is worth. Ask the seller how long they have owned it and whether they have a receipt or the original listing. A bike offered with no history, priced far below similar listings, and with fresh paint over an odd area of the frame deserves more scepticism than usual. If a seller refuses a test ride outright, treat that as information about the bike.
Frequently Asked Questions
Can I convert a fixed-gear bike to a freewheel, or the other way around?
If the rear hub is a flip-flop, you flip the wheel and re-tension the chain. Otherwise you need a new rear hub or wheel, and converting to fixed also requires a threaded lockring to stop the cog unthreading.
How do I check chain wear without a chain-wear tool?
Pull the chain forward off the front of the chainring at the three o'clock position. If you can lift it far enough to see daylight over a whole tooth, the chain is worn out.
Does the gear ratio matter when buying?
Yes, and it is worth asking. A ratio suited to flat city riding is punishing on hills, and changing it means a new cog or chainring — cheap, but not free, and it changes chain length too.
