Glossary

Every term used in the data, defined in plain English. How the numbers are computed is covered in the methodology; how to read them, in the FAQ.

MOT test: The annual roadworthiness inspection required for most road vehicles in Great Britain over three years old, run under DVSA rules.
Normal test: A bike's scheduled MOT inspection. All statistics here use normal tests only; retests, aborted and abandoned tests are excluded.
First-time pass rate: The share of normal tests passed at the first attempt with nothing to fix. The headline reliability number throughout this site.
Pass after rectification (PRS): A pass where a defect was found but fixed during the same visit. Counted separately from a clean first-time pass.
Outright fail: A test that ended in failure: the bike left needing work and a retest.
Advisory: A wear item the tester flags for future attention. Advisories do not fail a test and are excluded from all failure statistics here.
Defect: A recorded reason for failure, catalogued against a DVSA inspection item. One failed test can record several defects.
Component group: The DVSA inspection section a defect belongs to: lighting and signalling, brakes, steering and suspension, tyres and wheels, and so on. Failure tables group defects this way.
Test class 1 / class 2: The two motorcycle MOT classes: class 1 for machines up to 200cc, class 2 for everything larger, including sidecar outfits.
Engine capacity (cc): Engine displacement in cubic centimetres, as recorded at test. Used here to band bikes: 125s, A2-friendly 250–500cc, litre-plus.
Median mileage: The odometer reading of the middle bike at test: half read more, half less. Preferred to the average, which a few extreme odometers would distort.
Registration-year cohort: All bikes of a model first registered in the same year, tracked as a group. Cohort pass rates reveal a model's best and worst years.
Survivor bias: The tendency of the oldest cohorts to score well simply because the badly-kept examples already left the road. Read very old cohorts with this in mind.
Model family: Tester-entered model names are free text ("MT", "WW"), so this site groups them into canonical families using engine size and naming rules, so the MT-07 and MT07 are one family.
First use date: The date a bike first entered service, from which its registration year and age at test are derived.
Test year: The calendar year a test happened. Trend charts plot pass rate by test year.
DVSA: The Driver and Vehicle Standards Agency, the UK body that runs the MOT scheme and publishes the anonymised results dataset this site is built on.

Statistics on this site are licensed CC BY 4.0: cite bikereliability.co.uk and link the claim. Source data: DVSA anonymised MOT results, OGL v3.0.