Free printableMeasure partsTSP-ME-14
Brake shoe arc template — which drum size do you have?
True-size arcs at the two drum diameters the owner community reports. Lay the shoe on the page and see which one it belongs to.
Layout preview of page one. The PDF itself is typeset text, not an image.
Download — free, no email
3 pages. No account, no sign-up, no newsletter. Print it, copy it, hand it to somebody else.
TSP-ME-14 · version v1.0 · September 2026. Opens in your browser's PDF viewer, where you can print directly.
The problem it solves
Drum brake shoes are sold by diameter, and owners have no way of measuring the diameter of a curve accurately with a rule. The two common sizes are close enough that a wrong set will go into the backplate and then not contact the drum properly — which is a brake that feels fine on the drive and is not there when it is needed.
Measuring the diameter of an arc is genuinely difficult by hand. You cannot get a rule across the true diameter of a shoe because the shoe is only part of the circle, and measuring the chord and doing the geometry is not something anybody does in a shed.
Laying it on a printed arc is trivial, which is exactly the kind of problem paper solves and a screen does not.
The other half of this sheet is the link nobody makes: which drum size a machine has follows from its engine case length, not from its badge or its displacement. The owner community reports the shorter case paired with one drum size and the longer case with another. That is community consensus rather than a manufacturer document, so measure rather than assume — but it means a case-length measurement narrows your brake search before you have taken anything apart.
The mistakes this sheet exists to prevent
- Trying to measure a shoe's diameter with a rule across the open side, which cannot reach the true diameter.
- Ordering shoes on engine displacement. Drum size follows case length, not cc.
- Fitting shoes that go into the backplate but do not match the drum arc, giving a high pedal and poor contact.
- Not measuring the drum itself when the old shoes are worn beyond recognition.
- Ignoring the width of the shoe, which has to match the drum as well as the diameter does.
Who it is for
- Anyone replacing drum brake shoes on a scooter, moped or ATV
- Owners whose rear brake has never felt right since it was last worked on
- Anyone with a set of shoes in their hand and no idea what size they are
What is on it
- True-size arcs at the common drum diameters
- How to measure the drum itself when the shoes are unrecognisable
- The case-length link, with its sourcing stated honestly
- A record block for diameter, width and the actuating arrangement
How to use it
- 01Check the calibration rule first. An arc printed at 94% is a different diameter.
- 02Lay the shoe's friction face down on the arcs and slide it until one matches along its whole length.
- 03If the shoes are worn out of shape, measure the drum's inside diameter instead.
- 04Record the width as well as the diameter — both have to match.
Also in a pack
Use it with the registry
Other sheets you may want
- Brake pad measuring board — read all four dimensions at oncePush the pad into the corner and read all four dimensions off the page. Built because look-alike pads differ by millimetres and no photograph shows it.
- Short case or long case? How to tell, and why it decides everythingOne measurement and one count decide which drive belt, which wheel and which brake your engine takes. Take them before you shop, not after.
- Scooter brake service recordWhat was fitted, what it measured when it came off, and how long it lasted. For the system where guessing is least acceptable.
Free to print, copy, and share — including in forums, clubs and workshops. If you find a mistake on this sheet, tell us and it gets corrected. Quote TSP-ME-14 and the version so we know exactly which sheet you mean. All printables.