Bsa B31 vs Kawasaki ZXR400

The Bsa B31 passes its MOT first time more often than the Kawasaki ZXR400: 92.0% vs 73.1%, a 18.9-point lead.

MOT reliability, side by side

first-time pass rate, outright fail rate and tests analysed · 2005–2025

Metric	Bsa B31	Kawasaki ZXR400
First-time pass rate	92.0%	73.1%
Outright fail rate	3.1%	18.9%
Vs comparable bikes (age & mileage adjusted)	+12.2 pts	-9.9 pts
Engine size	350cc	398cc
Rank among all models	#470 of 5428	#4490 of 5428
Median miles at test	15,803	23,651
MOT tests analysed	3,429	14,200
Most common failure	lighting and signalling	lighting and signalling

First-time outcomes on normal tests, 2005–2025. "Most common failure" is the component group with the most recorded defects on failed tests. Read pass rates against test counts: a smaller sample is noisier. Source: DVSA anonymised MOT results.

"Vs comparable bikes" is the first-time pass rate minus the rate expected for each bike's own mix of age, mileage and test class, in percentage points: positive means better than comparable bikes. How this works.

What fails, side by side

share of each bike's MOT tests that failed on the component · lower is better

Component	Bsa B31	Kawasaki ZXR400
Lights & signalling	1.3%	9.1%
Brakes	1.3%	7.9%
Steering & suspension	1.1%	7.9%
Tyres & wheels	0.6%	4.0%
Fuel & exhaust	0.2%	2.4%
Structure & body	0.1%	2.2%
Drive system	0.3%	1.9%

A test that fails on two components counts once in each. Component links go to the bikes most likely to fail on it.

Pass rate by test year

first-time MOT pass rate in each calendar year both bikes were tested

Test year	Bsa B31	Kawasaki ZXR400
2009	92.4%	70.1%
2010	91.9%	68.5%
2011	89.8%	71.2%
2012	92.6%	69.5%
2013	83.1%	68.6%
2014	87.5%	70.6%
2015	100.0%	75.5%
2016	87.5%	75.6%

Each year mixes bikes of different ages, so a fleet that is getting older tends to slip.

Pass rate by mileage

first-time MOT pass rate by miles on the clock at test

Mileage	Bsa B31	Kawasaki ZXR400
0k-10k miles	91.6%	87.1%
10k-20k miles	92.8%	77.4%
20k-30k miles	92.0%	69.9%
30k-40k miles	91.9%	67.8%
40k-50k miles	90.3%	64.7%
50k-60k miles	93.0%	64.9%

Bands with fewer than 30 tests for either bike are left out.

Bsa B31 vs Kawasaki ZXR400 FAQ

answers computed from the data above · terms in the glossary

Which is more reliable, the Bsa B31 or the Kawasaki ZXR400?

The Bsa B31 passes its MOT first time more often than the Kawasaki ZXR400: 92.0% vs 73.1%, a 18.9-point lead. Adjusted for age, mileage and test class, the Bsa B31 still comes out ahead: +12.2 points vs comparable bikes for the Bsa B31, -9.9 for the Kawasaki ZXR400. An MOT checks roadworthiness items, not engine or gearbox internals.

What does the Bsa B31 fail its MOT on most?

Lights & signalling: 1.3% of Bsa B31 MOT tests failed on it, then brakes (1.3%).

What does the Kawasaki ZXR400 fail its MOT on most?

Lights & signalling: 9.1% of Kawasaki ZXR400 MOT tests failed on it, then brakes (7.9%).

Which holds up better at high mileage, the Bsa B31 or the Kawasaki ZXR400?

At 50k-60k miles the Bsa B31 passes first time more often: 93.0% for the Bsa B31 vs 64.9% for the Kawasaki ZXR400.

BSA B31 92.0% pass · 3,429 tests KAWASAKI ZXR400 73.1% pass · 14.2k tests

See each bike's full report (trend, mileage curve, failure breakdown and rivals) on its own page.