BSA M21

600cc Petrol Class 2

#364 of 5426 overall #16 of 62 BSAs #224 of 2787 other bikes

92.6%

first-time pass rate

2.3%

failed outright

22,787

median miles at test

996

MOT tests, 2005–2025

Pass rate over time

first-time pass rate by test year · 2006–2017

The M21's first-time pass rate has fallen 3.7 points since 2006, 90.8% to 87.1%.

Pass rate by mileage

how the M21's first-time pass rate falls with the odometer · class average 84.9%

A low-mileage M21 passes first time 92.4% of the time; by 50k that's 94.2%.

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 M21

failure defects by component group · advisories excluded

Component group	Defects	% of defects	vs all bikes
lighting and signalling	24	39.3	0.3×
steering and suspension	20	32.8	0.4×
tyres and wheels	5	8.2	0.3×
brakes	5	8.2	0.1×
fuel and exhaust	3	4.9	0.3×
sidecar	2	3.3	—
driving controls	1	1.6	0.4×
body and structure	1	1.6	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 M21 beats 4 of its 4 closest rivals (KAWASAKI ZX-6R, SUZUKI GSF600, YAMAHA FZS600).

KAWASAKI ZX-6R 78.1% pass · 174k tests SUZUKI GSF600 77.3% pass · 143k tests YAMAHA FZS600 82.6% pass · 137k tests SUZUKI SV650S 80.6% pass · 84.6k 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 M21.

Pass rate by registration year

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

Best year to buy used: 1957 (100.0% pass). Weakest: 1956 (86.0%).

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 M21 FAQ

answers computed from the data above · terms in the glossary

Is the BSA M21 reliable?

The BSA M21 is more reliable than average for its class: 92.6% of its 996 MOT tests (2005–2025) passed first time, against a class average of 84.9%. That ranks it #364 of 5426 models.

What does a M21 fail its MOT on most?

lighting and signalling — 39% of all defects recorded against failed M21 tests.

What is the best year of M21 to buy used?

By first-time pass rate, 1957-registered examples do best (100.0%) and 1956 worst (86.0%). Condition and history still trump the year.

How many miles will a M21 last?

The median M21 shows 22,787 miles at test, and examples around 50k miles still pass 94.2% of the time — mileage alone rarely kills one.