Frame Numbers Explained: How to Check a Bike Is Not Stolen

What Is a Frame Number?

Every bicycle has a unique serial number stamped into the frame during manufacturing. It's the bike equivalent of a car's VIN. No two bikes should have the same number.

This number is your best tool for:

• Verifying a bike isn't stolen before you buy it
• Proving ownership if your bike is stolen
• Insurance claims, most insurers require it
• Registration on theft databases like BikeRegister

Where to Find It

The location varies by manufacturer, but the most common spots are:

Bottom bracket shell (most common): Flip the bike upside down and look at the underside where the pedal cranks attach. You may need to clean off grime.

Head tube: The tube at the front where the fork goes through. Check the front, back, and underside.

Rear dropout: Where the rear wheel axle attaches to the frame. Less common on modern bikes.

Seat tube: Occasionally stamped low on the seat tube, near the bottom bracket.

The number is typically 6-12 characters, often a mix of letters and numbers. Some brands (Trek, Specialized) use longer codes that encode the model and year.

How to Check If a Bike Is Stolen

BikeRegister

The UK's national cycle database, used by all UK police forces. Search at bikeregister.com/bike-checker. It's free to check.

CheckThatBike

Another free tool that cross-references multiple databases.

Local police

You can ask your local police to run a serial number check. Some forces have online tools; others require a phone call.

Cyclesite

When you list a bike on Cyclesite, we automatically check the frame number against stolen bike databases. This protects both buyers and sellers.

What If the Frame Number Is Missing?

Some legitimate reasons a frame number might be hard to find:

• Paint over it, some resprays cover the serial number. Not ideal, but not necessarily sinister.
• Custom/hand-built frames, small builders sometimes don't stamp serial numbers, or stamp them in unusual locations.
• Very old bikes, pre-1990s bikes sometimes lack serial numbers.

Illegitimate reasons:

• Filed off, if the stamping area looks ground or filed smooth, the bike is almost certainly stolen. Walk away immediately and report it to the police.
• Seller refuses to share it, why? This alone is reason enough not to buy.

Registering Your Own Bike

If you own a bike, register it now, before it's stolen.

BikeRegister (£30 lifetime):

• Records your frame number, photos, and personal details
• Issues a tamper-evident sticker for your frame
• Police can instantly check if a recovered bike is registered
• Deters theft, research shows registered bikes are less likely to be targeted

Immobilise (free):

• Another national property database used by UK police
• Register any valuable item, not just bikes

For Sellers

Including your frame number in your listing does two things:

1. Builds instant trust, serious buyers will check it and feel confident
2. Filters out tyre-kickers, buyers who see the frame number know you're legitimate

On Cyclesite, adding your frame number is part of the listing process. It's verified automatically, so buyers can see the bike is clean before they even message you.

The Bigger Picture

Around 300,000 bikes are stolen in the UK every year. Only about 5% are recovered. Frame numbers are the single most effective tool for recovery, but they only work if bikes are registered and buyers check them.

Every time you check a frame number before buying, you make the stolen bike market slightly less profitable. It's a small act that compounds across the entire cycling community.