Question 1

What’s the single most common reason cars fail their MOT nationally?

Accepted Answer

"Coil spring: fractured or broken" - the single most frequently recorded fail item in the entire dataset, with 2,911,257 occurrences.

Question 2

What’s the most common advisory (not yet a fail) across all UK cars?

Accepted Answer

"Brake discs: in such a condition that it is seriously weakened" - flagged as an advisory 23,099,067 times, far more often than it’s ever recorded as an outright fail.

Question 3

How many MOT tests has Bib’s dataset analysed?

Accepted Answer

144,282,174 MOT tests, spanning 2,594 makes - the foundation every myth, fact and tip on this site is checked against.

Question 4

What % of UK cars fail their very first MOT at age 3?

Accepted Answer

15.5%, based on 53,051,496 first-MOT records - roughly one car in every six.

Question 5

Which vehicle type has the best overall MOT pass rate?

Accepted Answer

Motorcycles, by a wide margin - an 8% failure rate. Full ranking, best to worst: motorcycle 8% · other 16.4% · car 17.8% · van 21.6%.

Question 6

How much does pass rate change between a model’s best and worst year?

Accepted Answer

A lot. The widest example found: the Ford Fiesta swings by 29.6 percentage points between its best and worst model year - proof that "the model" isn’t one fixed reliability number.

Question 7

How many spelling/naming variants exist in raw government data for one popular car?

Accepted Answer

The Ford Fiesta alone has 20 distinct model-name strings in the raw DVSA data - a reminder of how messy the source records are before anyone cleans them up.

Question 8

What share of tested vehicles are over 10, 15 or 20 years old and still on the road?

Accepted Answer

72% of tests in the dataset are on cars over 10 years old, 36% over 15 years, and 13% over 20 years - most of the UK’s MOT-tested fleet is a lot older than showroom marketing would suggest.

Did You Know? MOT Facts From 144 Million Tests

How many MOT tests has Bib’s dataset analysed?

What’s the most common advisory (not yet a fail) across all UK cars?

What’s the single most common reason cars fail their MOT nationally?

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