Assembling a bike bought online: tools and checks
A bike bought online arrives in a box, roughly 85% assembled. The remaining 15% is the part that decides whether it is safe, and it is the part nobody reads the instructions for.
This guide covers what is actually in the box, the four tools you need, the bolts that matter and the checks to do before the first ride. It takes about 45 minutes the first time and ten minutes once you know how.
What is in the box
Almost every bike shipped in a carton arrives like this:
- Frame, wheels, drivetrain and brakes already fitted.
- Front wheel removed, usually with a quick-release skewer or a bolt-through axle in a bag.
- Handlebar and stem either removed or turned sideways.
- Pedals in a small bag, always separate.
- Saddle and seatpost fitted or loose.
- A multi-tool, usually a cheap one, and a spoke wrench.
- Reflectors and a bell, legally required in some markets and worth fitting in the UK.
- The charger, for an e-bike, in its own box.
What is not in the box, and what you will need:
- A track pump with a pressure gauge. The most important tool you will own.
- A set of hex keys (4, 5 and 6 mm covers most of a bike).
- A torque wrench that reads 2-15 Nm. This is the tool people skip and shouldn't.
- Grease and, ideally, carbon assembly paste if the bike has carbon parts.
The four bolts that matter, and their torque
Torque is measured in newton-metres (Nm). Overtightening crushes carbon and strips aluminium threads. Undertightening lets things move at the worst moment. A small torque wrench costs £25-40 and removes the guesswork.
These are the values that matter on almost every bike. Check your own manual, because the frame and component makers specify their own figures, but these are typical:
| Fastener | Typical torque | What happens if you get it wrong |
|---|---|---|
| Stem clamp bolts (steerer) | 5-6 Nm | Too loose: bars rotate under load. Too tight: crushes the steerer |
| Handlebar clamp bolts | 5-6 Nm | Too tight: cracks carbon bars |
| Seatpost clamp | 5-7 Nm | Too tight: cracks the frame at the slot |
| Saddle rail clamp | 6-8 Nm | Too loose: saddle tilts mid-ride |
| Pedals (into crank) | 35 Nm | Too loose: strips the crank thread |
| Wheel axle / quick-release | 8-10 Nm (thru-axle) | Too loose: wheel can leave the dropout |
Note the two extremes: stem bolts are delicate (5-6 Nm) and pedals need real force (35 Nm). These are not the same job and should not be done with the same feel.
The pedal thread trap
Pedals are left-hand threaded on the left side. That means the left pedal tightens anticlockwise, the opposite of almost everything else on a bike. Cross-threading a pedal into an aluminium crank is a common and expensive mistake: start it by hand, feel for smooth engagement, and only then use a spanner.
The left pedal is marked "L" and the right "R". Fit them to the matching side. Grease the threads first.
Step by step
1. Unpack without cutting the bike
Cut the tape, not the contents. Cardboard boxes contain zip ties, foam and sometimes a stray cable. Take everything out, lay it flat, and keep the box: you need it if you ever return the bike, and it is the only way to ship it.
2. Fit the front wheel
If it is a quick-release: slide the axle in, close the lever so it leaves an imprint in your palm, and make sure the lever is in the closed position (curved side in). If you can close it with two fingers, it is too loose.
If it is a thru-axle: thread it in by hand until it seats, then tighten to the specified torque. Never force it; if it does not thread smoothly, the axle is misaligned.
Check the brake rotor enters the caliper cleanly and does not rub. Spin the wheel: it should turn freely and stop without wobbling.
3. Straighten and fit the handlebar
Four bolts on the stem faceplate, tightened in a cross pattern (top-left, bottom-right, top-right, bottom-left) in small increments to 5-6 Nm. The gap between the faceplate and the stem should be even top and bottom. An uneven gap means uneven clamping, which is how carbon bars crack.
Set the bar angle so the brake levers are at roughly 45 degrees below horizontal, which is where your wrists naturally sit.
4. Fit the saddle and set the height
Grease the seatpost (except carbon, which gets assembly paste, never grease). Insert to at least the minimum insertion mark, which is printed on the post. Set the height with the heel method: heel on the pedal at the bottom of the stroke, leg almost straight.
5. Fit the pedals
By hand first, then 35 Nm. Left pedal anticlockwise into the left crank.
6. Inflate the tyres
The number on the sidewall is a maximum, not a recommendation. A mountain bike tyre rated to 50 psi should usually run at 22-28. A hybrid tyre rated to 80 should run at 50-65. See our tyre pressure guide for figures by rider weight.
7. Charge the battery (e-bikes)
Charge to full before the first ride. Most e-bike batteries ship at 30-50% for transport safety. Use only the charger supplied: the connector, voltage and current are matched to that battery, and a mismatched charger is a fire risk.
The ten-minute safety check
Do this before the first ride, and again after the first 50 km, because new cables stretch and new bolts settle.
- Wheels: both quick-releases or axles closed and tight. Lift the bike and spin each wheel; check for wobble and for brake rub.
- Brakes: pull each lever hard. It should not reach the handlebar. The bike should not roll when you hold the front brake and push forward.
- Headset: hold the front brake and rock the bike forward and back. Any clicking or movement means the headset is loose.
- Stem and bars: stand over the bike, hold the bars, and try to twist them against the front wheel. Nothing should move.
- Saddle: push down hard on it. It should not rotate or slide.
- Pedals: try to move each one sideways. No play.
- Tyres: firm, and check the sidewalls for damage from shipping.
- Chain: on the ring and cassette, not jammed behind the smallest cog.
- Bolts: a quick pass with the hex keys on anything you fitted.
- E-bike only: battery locked into the frame, display powers on, motor engages when you pedal, and the brakes cut the motor.
If any of those fail, stop and fix it before riding. A bike that fails the headset or brake check is not safe at any speed.
What to do after the first 50 km
New bikes settle. After the first few rides:
- Check every bolt you fitted with the torque wrench again. They will have moved.
- Check the gear indexing. Cables stretch and gears start to skip. A quarter turn of the barrel adjuster usually fixes it.
- Check spoke tension by squeezing pairs of spokes; they should feel similar. A wheel that has gone out of true in the first 50 km is usually a tension issue, not damage.
- Re-check tyre pressure. New tubes lose pressure faster in the first week.
Many local bike shops offer a free or cheap first service at 4-6 weeks for bikes bought from them. If you bought online, a £30-50 check-over at a local shop is money well spent, particularly on an e-bike where the motor and battery connections are worth a professional look.