Ariel Square Four: MOT pass rate by registration year

Which Square Four years pass first time, and which fall short of the model's 91.4% average, from 555 DVSA tests.

1958

highest-passing year · 93.5%

1957

lowest-passing year · 91.1%

2.4pp

spread across 3 years

Pass rate by registration year

first-time pass rate · cohorts with 50 or more tests · registration year from first use date

Highest pass rate: 1958 (93.5% of 93 tests). Lowest: 1957 (91.1% of 56).

Registered	Tests	First-time pass	vs model (91.4%)
1953	57	93.0%	+1.6 pp
1957	56	91.1%	-0.3 pp
1958	93	93.5%	+2.1 pp

Older cohorts are survivors: the worst examples have already left the road, which tends to lift the earliest years. A first-time MOT pass is a roadworthiness check, not a full mechanical inspection.

Pass rate over time

first-time pass rate by test year · 2006–2012

Questions

Which Square Four years have the lowest MOT pass rate?: none: no registration year of the Ariel Square Four falls more than two points under the model's 91.4% overall pass rate.
Which Square Four year has the highest MOT pass rate?: 1958, at 93.5% of 93 first tests (2005–2025).
How much does the Square Four pass rate vary by year?: 2.4 percentage points between the highest (1958, 93.5%) and lowest (1957, 91.1%) cohorts with at least 50 tests. Older cohorts are survivors: the worst examples have already left the road, which tends to lift the earliest years.

Full report: Ariel Square Four reliability, failures and mileage · ranked #588 of 5428 models· other Ariel models: Arrow, Red Hunter, Leader, Huntmaster, NH, VH