ARIEL SQUARE FOUR
The pass rate is the MOT first-time pass: a roadworthiness check of the items an MOT covers (brakes, lights, tyres, steering, structure, emissions), not a full mechanical inspection of engine or gearbox internals. It is a reliability signal, not a complete measure of mechanical reliability. What this measures.
Pass rate over time
The SQUARE FOUR's first-time pass rate has held steady since 2006 (93.4% → 92.6%).
Pass rate by mileage
A low-mileage SQUARE FOUR passes first time 89.5% of the time; by 50k that's 94.7%.
First-time pass rate by odometer reading at test, 10,000-mile bands for this model. Mileage is the strongest reliability signal. See the full curve.
What fails on a SQUARE FOUR
| Component group | Share of defects | Defects | % of defects | vs all bikes |
|---|---|---|---|---|
| brakes |
|
6 | 37.5 | 0.2× |
| steering and suspension |
|
4 | 25 | 0.2× |
| lighting and signalling |
|
3 | 18.8 | 0.1× |
| tyres and wheels |
|
2 | 12.5 | 0.1× |
| lamps and reflectors |
|
1 | 6.2 | 0.1× |
Defects recorded against failed normal tests, 2005–2025, grouped by DVSA inspection section. One test can record multiple defects. "vs all bikes" is how often this model's tests record a defect in the group, as a multiple of the all-bike rate.
How rivals compare
On first-time pass rate the SQUARE FOUR beats 3 of its 4 closest rivals (BMW R1200, BMW R1150, TRIUMPH SPRINT).
Rivals share this bike's type and sit within ±30% of its engine capacity, ≥ 5,000 tests. Card colour = better/worse first-time pass rate than the SQUARE FOUR.
Compare with any bike
More ARIEL models
Pass rate by registration year
Best year to buy used: 1958 (93.5% pass). Weakest: 1957 (91.1%).
First-time pass rate by the year each bike was first registered (cohorts with ≥ 50 tests). Older cohorts are survivors: the worst examples have already left the road, which tends to lift the earliest years.
ARIEL SQUARE FOUR FAQ
Is the ARIEL SQUARE FOUR reliable?
The ARIEL SQUARE FOUR is more reliable than average for its class: 91.4% of its 555 MOT tests (2005–2025) passed first time, against a class average of 84.9%. That ranks it #588 of 5428 models.
What does a SQUARE FOUR fail its MOT on most?
brakes — 38% of all defects recorded against failed SQUARE FOUR tests.
What is the best year of SQUARE FOUR to buy used?
By first-time pass rate, 1958-registered examples do best (93.5%) and 1957 worst (91.1%). Condition and history still trump the year.
How many miles will a SQUARE FOUR last?
The median SQUARE FOUR shows 11,764 miles at test, and examples around 50k miles still pass 94.7% of the time — mileage alone rarely kills one.
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Free to embed on your site, blog or forum — a live Ariel Square Four reliability card that stays up to date and links back here. More on the free API page.