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.
“vs expected” adjusts for age, mileage and test class, so a cherished classic and a hard-used commuter are compared fairly. How this works.
Pass rate over time
The B40's first-time pass rate has fallen 3.1 points since 2005, 98.3% to 95.2%.
Pass rate by mileage
A low-mileage B40 passes first time 91.2% of the time; by 50k that's 90.2%.
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 B40
| Component group | Share of defects | Defects | % of defects | vs all bikes |
|---|---|---|---|---|
| steering and suspension |
|
90 | 31.9 | 0.6× |
| lighting and signalling |
|
86 | 30.5 | 0.4× |
| tyres and wheels |
|
37 | 13.1 | 0.4× |
| brakes |
|
30 | 10.6 | 0.2× |
| body and structure |
|
10 | 3.5 | 0.6× |
| drive system |
|
9 | 3.2 | 0.4× |
| fuel and exhaust |
|
8 | 2.8 | 0.3× |
| driving controls |
|
5 | 1.8 | 0.6× |
| Items Not Tested |
|
4 | 1.4 | 1.3× |
| reg plates and vin |
|
3 | 1.1 | 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 B40 beats 4 of its 4 closest rivals (SUZUKI AN400, SUZUKI DR-Z400S, YAMAHA RD350).
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 B40.
Compare with any bike
More BSA models
Pass rate by registration year
Best year to buy used: 1969 (95.7% pass). Weakest: 1968 (85.7%).
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.
BSA B40 FAQ
Is the BSA B40 reliable?
The BSA B40 is more reliable than average for its class: 90.6% of its 3,360 MOT tests (2005–2025) passed first time, against a class average of 84.9%. That ranks it #776 of 5428 models.
What does a B40 fail its MOT on most?
steering and suspension — 32% of all defects recorded against failed B40 tests.
What is the best year of B40 to buy used?
By first-time pass rate, 1969-registered examples do best (95.7%) and 1968 worst (85.7%). Condition and history still trump the year.
How many miles will a B40 last?
The median B40 shows 8,069 miles at test, and examples around 50k miles still pass 90.2% of the time — mileage alone rarely kills one.
Embed this bike
Free to embed on your site, blog or forum — a live Bsa B40 reliability card that stays up to date and links back here. More on the free API page.