Ajs 18S vs Yamaha FZS600

The Ajs 18S passes its MOT first time more often than the Yamaha FZS600: 92.8% vs 82.6%, a 10.2-point lead.

MOT reliability, side by side

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

Metric	Ajs 18S	Yamaha FZS600
First-time pass rate	92.8%	82.6%
Outright fail rate	3.0%	10.6%
Engine size	500cc	599cc
Rank among all models	#330 of 5428	#3052 of 5428
Median miles at test	14,829	21,612
MOT tests analysed	598	136,558
Most common failure	lighting and signalling	brakes

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.

What fails, side by side

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

Component	Ajs 18S	Yamaha FZS600
Lights & signalling	1.8%	3.4%
Brakes	0.5%	4.5%
Steering & suspension	1.2%	2.7%
Tyres & wheels	0%	2.9%
Fuel & exhaust	0.2%	1.1%
Structure & body	0.2%	1.1%
Drive system	0.2%	0.9%

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	Ajs 18S	Yamaha FZS600
2006	95.6%	86.0%
2007	97.5%	84.1%
2008	95.8%	83.4%
2009	88.2%	81.2%
2010	88.6%	82.0%
2011	89.6%	81.1%
2012	93.3%	80.2%

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	Ajs 18S	Yamaha FZS600
0k-10k miles	93.2%	89.6%
10k-20k miles	97.2%	85.5%
20k-30k miles	90.5%	81.4%
30k-40k miles	88.6%	78.7%
40k-50k miles	92.6%	76.8%
50k-60k miles	84.4%	74.7%

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

Ajs 18S vs Yamaha FZS600 FAQ

answers computed from the data above · terms in the glossary

Which is more reliable, the Ajs 18S or the Yamaha FZS600?

The Ajs 18S passes its MOT first time more often than the Yamaha FZS600: 92.8% vs 82.6%, a 10.2-point lead. An MOT checks roadworthiness items, not engine or gearbox internals.

What does the Ajs 18S fail its MOT on most?

Lights & signalling: 1.8% of Ajs 18S MOT tests failed on it, then steering & suspension (1.2%).

What does the Yamaha FZS600 fail its MOT on most?

Brakes: 4.5% of Yamaha FZS600 MOT tests failed on it, then lights & signalling (3.4%).

Which holds up better at high mileage, the Ajs 18S or the Yamaha FZS600?

At 50k-60k miles the Ajs 18S passes first time more often: 84.4% for the Ajs 18S vs 74.7% for the Yamaha FZS600.

AJS 18S 92.8% pass · 598 tests YAMAHA FZS600 82.6% pass · 137k tests

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