How do I choose a tank bag that fits my machine?

By attachment, before anything else. A magnetic bag needs a steel tank — plenty of modern machines have plastic or aluminium ones. Straps fit anything and cross the paint. A ring system is specific to your machine and the quickest to release.

Establish what your tank is made of

This is the single most common mismatched purchase in the family. A magnet on a plastic or aluminium tank holds nothing, and the tank material is not always obvious from looking. The manual or the maker answers it.

What each attachment costs you

Magnetic: fastest to fit and remove, and it traps grit against the paint if the tank is not clean. Strap: universal, slower, and webbing crosses painted surfaces. Ring: a ring replaces the fuel cap surround and the bag clips to it — most secure, fastest release, and a two-part purchase because the ring is machine-specific.

Capacity, and the part that is published as a range

Many bags expand with a zip, which is why capacity is often given as two numbers. An expanded bag sits higher, which matters if you lean forward — worth checking against your own riding position rather than a photograph.

The features that decide daily use

A top pocket that can be worked with gloves on. A carry strap, because the bag comes off at every stop and has to go somewhere. And a waterproof cover, almost always supplied and almost never as good as a sealed bag — which is worth knowing before a long wet day.

Where makers help and where they do not

Those who list compatible machines have done the work for you. Where no list exists, the tank shape in your own case is what decides, and a photograph of a different tank tells you nothing.