Data as of: DVSA MOT results to 2025
Harley-Davidson XL 1200 Low Sportster vs Triumph Thunderbird
The Harley-Davidson XL 1200 Low Sportster passes its MOT first time more often than the Triumph Thunderbird: 90.4% vs 87.8%, a 2.6-point lead.
MOT reliability, side by side
| Metric | Harley-Davidson XL 1200 Low Sportster | Triumph Thunderbird |
|---|---|---|
| First-time pass rate | 90.4% | 87.8% |
| Outright fail rate | 4.5% | 6.2% |
| Vs comparable bikes (age & mileage adjusted) | +3.6 pts | +2.1 pts |
| Engine size | 1,200cc | 885cc |
| Rank among all models | #825 of 5428 | #1669 of 5428 |
| Median miles at test | 8,973 | 13,106 |
| MOT tests analysed | 3,435 | 56,312 |
| Most common failure | lamps and reflectors | 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.
"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
| Component | Harley-Davidson XL 1200 Low Sportster | Triumph Thunderbird |
|---|---|---|
| Lights & signalling | 2.1% | 2.2% |
| Brakes | 0.7% | 2.0% |
| Tyres & wheels | 0.8% | 1.6% |
| Steering & suspension | 0.5% | 1.3% |
| Structure & body | 0.5% | 0.3% |
| Fuel & exhaust | 0.2% | 0.4% |
| Drive system | 0.0% | 0.2% |
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
| Test year | Harley-Davidson XL 1200 Low Sportster | Triumph Thunderbird |
|---|---|---|
| 2018 | 92.4% | 87.8% |
| 2019 | 88.0% | 87.7% |
| 2020 | 94.7% | 88.8% |
| 2021 | 94.1% | 88.2% |
| 2022 | 90.4% | 88.9% |
| 2023 | 88.1% | 90.5% |
| 2024 | 85.3% | 88.2% |
| 2025 | 88.4% | 89.5% |
Each year mixes bikes of different ages, so a fleet that is getting older tends to slip.
Pass rate by mileage
| Mileage | Harley-Davidson XL 1200 Low Sportster | Triumph Thunderbird |
|---|---|---|
| 0k-10k miles | 92.2% | 90.5% |
| 10k-20k miles | 90.0% | 87.3% |
| 20k-30k miles | 85.8% | 85.4% |
| 30k-40k miles | 80.8% | 84.3% |
| 40k-50k miles | 82.4% | 83.2% |
Bands with fewer than 30 tests for either bike are left out.
Harley-Davidson XL 1200 Low Sportster vs Triumph Thunderbird FAQ
Which is more reliable, the Harley-Davidson XL 1200 Low Sportster or the Triumph Thunderbird?
The Harley-Davidson XL 1200 Low Sportster passes its MOT first time more often than the Triumph Thunderbird: 90.4% vs 87.8%, a 2.6-point lead. Adjusted for age, mileage and test class, the Harley-Davidson XL 1200 Low Sportster still comes out ahead: +3.6 points vs comparable bikes for the Harley-Davidson XL 1200 Low Sportster, +2.1 for the Triumph Thunderbird. An MOT checks roadworthiness items, not engine or gearbox internals.
What does the Harley-Davidson XL 1200 Low Sportster fail its MOT on most?
Lights & signalling: 2.1% of Harley-Davidson XL 1200 Low Sportster MOT tests failed on it, then tyres & wheels (0.8%).
What does the Triumph Thunderbird fail its MOT on most?
Lights & signalling: 2.2% of Triumph Thunderbird MOT tests failed on it, then brakes (2.0%).
Which holds up better at high mileage, the Harley-Davidson XL 1200 Low Sportster or the Triumph Thunderbird?
They are level: at 40k-50k miles the Harley-Davidson XL 1200 Low Sportster passes 82.4% first time and the Triumph Thunderbird 83.2%.
See each bike's full report (trend, mileage curve, failure breakdown and rivals) on its own page.