Ariel Square Four vs BMW R1150

The Ariel Square Four passes its MOT first time more often than the BMW R1150: 91.4% vs 88.5%, a 2.9-point lead.

MOT reliability, side by side

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

Metric	Ariel Square Four	BMW R1150
First-time pass rate	91.4%	88.5%
Outright fail rate	2.0%	6.8%
Engine size	1,000cc	1,130cc
Rank among all models	#588 of 5428	#1449 of 5428
Median miles at test	11,764	33,151
MOT tests analysed	555	170,963
Most common failure	brakes	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	Ariel Square Four	BMW R1150
Brakes	0.7%	2.9%
Lights & signalling	0.7%	2.4%
Steering & suspension	0.5%	1.4%
Tyres & wheels	0.2%	1.7%
Structure & body	0%	0.2%
Fuel & exhaust	0%	0.1%

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	Ariel Square Four	BMW R1150
2006	93.4%	91.8%
2007	94.9%	90.6%
2008	89.2%	89.3%
2009	92.9%	87.4%
2010	91.2%	88.3%
2011	83.6%	87.3%
2012	92.6%	87.6%

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	Ariel Square Four	BMW R1150
0k-10k miles	89.5%	92.9%
10k-20k miles	90.5%	92.1%
20k-30k miles	90.0%	90.1%
30k-40k miles	96.0%	88.6%
40k-50k miles	97.5%	86.9%
50k-60k miles	94.7%	85.7%

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

Ariel Square Four vs BMW R1150 FAQ

answers computed from the data above · terms in the glossary

Which is more reliable, the Ariel Square Four or the BMW R1150?

The Ariel Square Four passes its MOT first time more often than the BMW R1150: 91.4% vs 88.5%, a 2.9-point lead. An MOT checks roadworthiness items, not engine or gearbox internals.

What does the Ariel Square Four fail its MOT on most?

Brakes: 0.7% of Ariel Square Four MOT tests failed on it, then lights & signalling (0.7%).

What does the BMW R1150 fail its MOT on most?

Brakes: 2.9% of BMW R1150 MOT tests failed on it, then lights & signalling (2.4%).

Which holds up better at high mileage, the Ariel Square Four or the BMW R1150?

At 50k-60k miles the Ariel Square Four passes first time more often: 94.7% for the Ariel Square Four vs 85.7% for the BMW R1150.

ARIEL SQUARE FOUR 91.4% pass · 555 tests BMW R1150 88.5% pass · 171k tests

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