Finding parts
How to measure a CVT belt when the markings have worn off
The drive belt is the part most often ordered wrong on these machines, and the reason is structural: the marking wears off before the belt does, and a worn belt measures narrower than the one that will replace it.
6 min read
A drive belt is the part most often ordered wrong on a Chinese scooter, and the reason is almost never carelessness. It is that the belt carries three numbers, nobody explains which is which, the numbers wear off before the belt does, and the belt you are measuring is already narrower than the one you need to replace it with.
All four of those problems have the same answer, and it is not a size chart.
The three numbers, and which is which
A belt marking usually reads as three numbers with spaces between them — something in the form 743 20 30. Read left to right they are:
- Outside length in millimetres. Measured round the outer face of the belt, not the inner one, and not across the pulleys.
- Top width in millimetres. The wide flat face, at its widest point.
- Included angle in degrees. How steeply the two sides taper in towards the base.
That reading convention is consistent across sellers, manufacturers and owners, and it is consistent with what is actually printed on the belts. What we have not found is a standards document that defines it — so we describe it as a reliable trade convention rather than as a specification, and the sheet that goes with this article tells you how to confirm it against the belt in your hand in about ten seconds.
Why the marking goes first
The marking is printed on the flat outer face. That is the surface running against the clutch bell and the outer pulley faces, so it is the surface that gets polished away. On a belt that has done real mileage the marking is usually the first thing to go, which is exactly backwards from what you want — the belts most in need of replacing are the ones least able to tell you what they are.
Before you conclude yours is blank, clean it. Wipe the outer face with a rag and a little degreaser and look again in raking light. A surprising proportion of “unmarked” belts are simply dirty.
Measuring a belt with nothing printed on it
Length. Lay the belt flat on a bench so it forms an oval rather than a figure of eight. Run a length of string round the outside face, pull it snug without stretching the belt, and mark where the string meets itself. Measure the string. That is the outside length, and it is the number a seller means when they quote the first figure.
Width. Measure across the wide flat face at the widest point you can find, away from any glazed or frayed edge. If you do not have calipers, this is where a printed true-size scale earns its keep: lay the belt across a set of exact-width bars and read off the one that matches.
Angle. You cannot measure this reliably with a rule. Compare the belt end-on against printed profiles at actual size — the CVT belt gauge exists for precisely this, and it is the one measurement where a printed sheet genuinely beats a tape measure.
Telling a worn belt from a wrong belt
Here is the trap that catches people who do everything else right. A belt wears narrower, not shorter. So if you measure a well-used belt and order that width, you order a belt that was already too narrow when it was new. The machine will slip from the first mile.
If the width is still printed on the belt, compare it against what you measure — the difference is how much life it has had. If it is not, treat your measured width as a minimum and expect the correct new belt to be a little wider. The other signs a belt is finished are visible rather than dimensional:
- Cracks running across the cogs on the inner face
- Sides glazed and shiny, which means it has been slipping
- Edges worn to a sharp taper rather than a square shoulder
- Frayed or missing cogs anywhere along its length
Before you order
Write down all three numbers, plus what the belt came off. A seller working from “150cc scooter” is guessing. A seller working from a length, a width, an engine family number and the fact that your CVT cover has ten bolts is not.
There is a free sheet for this. The CVT belt measuring sheet has the reading convention, true-size width bars from 15mm to 22mm, a printed calibration rule and a record block, in Letter and A4. No account, no email. And if you have not yet worked out what engine you have, start there — the belt is downstream of that answer.
More from the registry
Source. US EPA annual certification data — EPA Certified Highway Motorcycle Test Results, MY2006-present; EPA Certified Off-Road Motorcycle / ATV / UTV / Rec Vehicle, MY2006-present. Retrieved 2026-09-07. Full provenance and method.