Bike serial number: where to find it, why to write it down
The serial number is engraved or stuck on the frame, usually under the bottom bracket. Write it down today, with a photo: once the bike is stolen, there is no frame left to turn over.
Where is the serial number?
Turn the bike over and look under the bottom bracket, where the tubes meet, level with the pedals. That is the most common place. What some manufacturers say:
- Cube: engraved under the bottom bracket, and repeated on the label in the service booklet.
- BMC: on or under the bottom bracket, beneath a QR code since the 2014 models.
- Cannondale (recent models): under the frame, by the cranks, with a barcode.
- Canyon: a sticker with a QR code near the bottom bracket.
- Decathlon: under the bottom bracket, electric bikes included.
The place varies from one manufacturer to another. If you see nothing, clean the area and look over the rest of the frame. Still nothing: the purchase invoice sometimes shows it, and the shop that sold the bike can help.
And on an electric bike?
The frame has its number, in the same place as on an ordinary bike. The battery and the motor often have their own numbers, and where they are depends on the supplier. Note those too.
Serial number or marking: what is the difference?
They are two separate numbers.
- The serial number is put on by the manufacturer. Its format changes from brand to brand, and it is not linked to any owner.
- The marking number has 10 characters. It is registered in the FNUCI, France’s national register of marked bikes, with your contact details. It has been compulsory since 1 January 2021 on new bikes sold by a business, and since 1 July 2021 on second-hand bikes sold by a business.
Marking has not replaced the serial number: the two complement each other. The details are in Bike marking in France: the law and what it changes.
Why write it down before a theft?
Because this number is what links a bike that is found back to you.
- The complaint. The police rely on your complaint and on proof that the bike is yours: serial or marking number, invoice, photos of its distinctive marks. Without a complaint, a bike that is found cannot be identified as stolen. In Rennes, in June 2026, a bike spotted on Leboncoin was not returned to its owner for that reason.
- Insurance. Bike insurers often ask for the serial number to identify the bike when you make a claim.
- A marked bike. Police officers and gendarmes (France’s other police force) check the national register and can contact the owner. In 2024, 11.4% of marked bikes reported stolen were found.
For the complaint itself, see Reporting a bike theft in France: where, how, what to bring.
How to keep it so it is useful
- Photograph the number up close, sharp and readable. Take a second photo that shows where it is on the frame.
- Copy it out as text, character by character. Watch for mix-ups between O and 0, I and 1.
- Keep it with the invoice, the marking number if there is one, and photos of the whole bike and its distinctive marks: a scratch, a sticker, an accessory.
- Keep a copy somewhere other than your phone.
On Retrace, the free bike record keeps the bike’s description, its numbers and its photos. If the bike is stolen, it is the basis of the file for your complaint. You make the complaint yourself.