Data as of: DVSA MOT results to 2025
Harley-Davidson XL 1200 C Custom Sportster 12 vs Triumph Thunderbird
The Harley-Davidson XL 1200 C Custom Sportster 12 passes its MOT first time more often than the Triumph Thunderbird: 94.0% vs 87.8%, a 6.2-point lead.
MOT reliability, side by side
| Metric | Harley-Davidson XL 1200 C Custom Sportster 12 | Triumph Thunderbird |
|---|---|---|
| First-time pass rate | 94.0% | 87.8% |
| Outright fail rate | 2.5% | 6.2% |
| Vs comparable bikes (age & mileage adjusted) | +6.3 pts | +2.1 pts |
| Engine size | 1,202cc | 885cc |
| Rank among all models | #172 of 5428 | #1669 of 5428 |
| Median miles at test | 7,049 | 13,106 |
| MOT tests analysed | 714 | 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 C Custom Sportster 12 | Triumph Thunderbird |
|---|---|---|
| Lights & signalling | 0.7% | 2.2% |
| Brakes | 0.4% | 2.0% |
| Tyres & wheels | 0.8% | 1.6% |
| Steering & suspension | 0.4% | 1.3% |
| Fuel & exhaust | 0.4% | 0.4% |
| Structure & body | 0.1% | 0.3% |
| Drive system | 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 C Custom Sportster 12 | Triumph Thunderbird |
|---|---|---|
| 2018 | 87.9% | 87.8% |
| 2019 | 96.6% | 87.7% |
| 2020 | 94.1% | 88.8% |
| 2021 | 96.7% | 88.2% |
| 2022 | 96.8% | 88.9% |
| 2023 | 93.8% | 90.5% |
| 2024 | 94.2% | 88.2% |
| 2025 | 98.0% | 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 C Custom Sportster 12 | Triumph Thunderbird |
|---|---|---|
| 0k-10k miles | 93.9% | 90.5% |
| 10k-20k miles | 94.9% | 87.3% |
| 20k-30k miles | 91.9% | 85.4% |
Bands with fewer than 30 tests for either bike are left out.
Harley-Davidson XL 1200 C Custom Sportster 12 vs Triumph Thunderbird FAQ
Which is more reliable, the Harley-Davidson XL 1200 C Custom Sportster 12 or the Triumph Thunderbird?
The Harley-Davidson XL 1200 C Custom Sportster 12 passes its MOT first time more often than the Triumph Thunderbird: 94.0% vs 87.8%, a 6.2-point lead. Adjusted for age, mileage and test class, the Harley-Davidson XL 1200 C Custom Sportster 12 still comes out ahead: +6.3 points vs comparable bikes for the Harley-Davidson XL 1200 C Custom Sportster 12, +2.1 for the Triumph Thunderbird. An MOT checks roadworthiness items, not engine or gearbox internals.
What does the Harley-Davidson XL 1200 C Custom Sportster 12 fail its MOT on most?
Tyres & wheels: 0.8% of Harley-Davidson XL 1200 C Custom Sportster 12 MOT tests failed on it, then lights & signalling (0.7%).
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 C Custom Sportster 12 or the Triumph Thunderbird?
At 20k-30k miles the Harley-Davidson XL 1200 C Custom Sportster 12 passes first time more often: 91.9% for the Harley-Davidson XL 1200 C Custom Sportster 12 vs 85.4% for the Triumph Thunderbird.
See each bike's full report (trend, mileage curve, failure breakdown and rivals) on its own page.