BSA B31

350cc Petrol Class 2

#468 of 5426 overall #21 of 62 BSAs #287 of 2787 other bikes

92.0%

first-time pass rate

3.1%

failed outright

15,803

median miles at test

3,429

MOT tests, 2005–2025

Pass rate over time

first-time pass rate by test year · 2005–2016

The B31's first-time pass rate has fallen 8.3 points since 2005, 95.8% to 87.5%.

Pass rate by mileage

how the B31's first-time pass rate falls with the odometer · class average 84.9%

A low-mileage B31 passes first time 91.6% of the time; by 50k that's 93.0%.

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 B31

failure defects by component group · advisories excluded

Component group	Defects	% of defects	vs all bikes
lighting and signalling	83	31.8	0.3×
brakes	59	22.6	0.3×
steering and suspension	56	21.5	0.4×
tyres and wheels	26	10	0.3×
drive system	12	4.6	0.4×
fuel and exhaust	7	2.7	0.3×
Items Not Tested	6	2.3	1.6×
body and structure	5	1.9	0.3×
driving controls	4	1.5	0.5×
reg plates and vin	3	1.1	0.2×

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

same type, similar capacity, high test volume

On first-time pass rate the B31 beats 4 of its 4 closest rivals (SUZUKI AN400, SUZUKI DR-Z400S, YAMAHA RD350).

SUZUKI AN400 86.2% pass · 27.1k tests SUZUKI DR-Z400S 80.4% pass · 26.8k tests YAMAHA RD350 86.3% pass · 19.6k tests KAWASAKI ZXR400 73.1% pass · 14.2k tests

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 B31.

Pass rate by registration year

how each model-year cohort fares · registration year from first use date

Best year to buy used: 1951 (98.4% pass). Weakest: 1952 (87.8%).

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 B31 FAQ

answers computed from the data above · terms in the glossary

Is the BSA B31 reliable?

The BSA B31 is more reliable than average for its class: 92.0% of its 3,429 MOT tests (2005–2025) passed first time, against a class average of 84.9%. That ranks it #468 of 5426 models.

What does a B31 fail its MOT on most?

lighting and signalling — 32% of all defects recorded against failed B31 tests.

What is the best year of B31 to buy used?

By first-time pass rate, 1951-registered examples do best (98.4%) and 1952 worst (87.8%). Condition and history still trump the year.

How many miles will a B31 last?

The median B31 shows 15,803 miles at test, and examples around 50k miles still pass 93.0% of the time — mileage alone rarely kills one.