Ask any MOT tester in our bay what fails most and they won't need to check a database. Tyres, suspension, brakes, lights, and visibility problems come through Plympton Car Centre every single week, in roughly the same order, for roughly the same reasons.
We test cars from Plymouth, Plympton, Ivybridge, and the villages further out along the A38 and the lanes towards Dartmoor. Those roads leave a mark on a car, and it usually shows up on the ramp long before the MOT test even starts. Here's what we see most, why it happens, and what stops it catching you out.
1. Tyres
More cars leave our bay with a tyre fail than for any other single reason. One independent study of over 40 million MOT tests put tyre faults at close to four in every ten failures nationally, and that lines up with what comes across our ramp.
The legal minimum tread depth is 1.6mm across the central three quarters of the tyre, all the way round. The AA recommends changing tyres nearer 3mm, because grip and stopping distance drop off well before you hit the legal limit, especially in the wet.
The tyres we fail most often haven't worn down evenly. A car that spends a lot of time on the back lanes around Yealmpton or Cornwood tends to pick up sidewall damage and uneven wear from potholes and camber changes that a motorway commute would never cause. We regularly find a bulge or a scuffed sidewall on a tyre that still has plenty of tread left, and that's an instant fail on its own.
A few checks take five minutes in your driveway:
- Push a 20p coin into the main grooves at several points, not just the middle. If the outer rim of the coin is covered, you're fine.
- Run a hand round the sidewall feeling for bulges, cracks, or cuts, particularly on the inside edge where you can't see it easily.
- Check the date code on the sidewall. A tyre with plenty of tread can still fail on age if it's perished, which happens more on cars that don't cover many miles.
2. Suspension
Suspension is the one that catches people out, because a worn bush or a cracked spring doesn't always feel dramatic from the driver's seat. It's usually our second most common failure, and on cars that do a lot of rural mileage it sometimes overtakes tyres.
The tester checks springs, dampers, and the joints and bushes that connect them to the rest of the car, looking for wear, corrosion, and how securely everything is mounted. A corroded coil spring can fracture without much warning, and a worn anti-roll bar link shows up as a clunk over speed bumps long before it becomes a full failure.
We see this most on cars that regularly use the lanes around Ivybridge, Bickleigh, and the routes onto the moor, where potholes and broken edges are a fact of life. A car doing mostly town driving around Plymouth wears far more evenly.
If you're hearing a knock or clunk over bumps that wasn't there a year ago, that's worth a look before your test date, not after.
3. Brakes
Brakes are the third biggest reason cars fail with us, and the South Hams terrain plays a real part in that. Long descents into Plymouth and the hills around Plympton work brakes harder than flat commuter routes elsewhere in the country, and that shows up as thinner pads and more heavily scored discs than you'd expect for the mileage.
Being this close to the coast adds another factor. Salt-laden air corrodes brake pipes and calipers faster on cars that sit outside overnight near the water, even ones that are otherwise well looked after mechanically.
The MOT test covers pad and disc condition, pipe and hose integrity, fluid condition, and how effectively the handbrake holds. A spongy pedal, a pull to one side under braking, or a handbrake that needs pulling further than it used to are all signs worth acting on before they become a fail sheet.
4. Lights and signalling
This is the one that frustrates us most, because it's the cheapest problem to prevent and one of the most common reasons a car fails. Nationally it's often cited as the single biggest category of MOT failures, sometimes close to three in every ten.
Almost none of these are expensive. A blown bulb, a hazy lens, or a cracked indicator cover is usually a five minute fix, but it still stops a car passing on the day. The number plate light is the one owners forget most, simply because you can't see it from the driver's seat.
Before your test, get someone to stand behind the car while you run through every light: brake lights, indicators, reverse light, fog light if fitted, and the number plate light. It takes two minutes and it's the easiest fail on this list to avoid entirely.
5. Visibility
Wipers, windscreen condition, and mirrors round out our top five, and rural driving conditions make this more of an issue here than it might be for a city-only driver. Dust and grit thrown up from hedgerows and farm traffic wear wiper blades down faster, and loose stone chippings on some of the lanes around us are a common cause of windscreen chips.
The zone directly in front of the driver is judged more strictly than the rest of the windscreen. A chip or crack there that would be fine at the edge of the glass can be enough to fail the test on its own.
Check your wiper blades for splitting or smearing, top up the washer fluid and make sure it actually reaches the glass, and get any chip in your direct line of sight looked at sooner rather than later. Repair is usually far cheaper than replacement if it's caught early.
What we do before every test
Between them, these five areas account for the large majority of what fails at MOT time, here and everywhere else. That's why our pre-MOT check works through exactly this list before your car goes anywhere near the test bay. For a thorough list of what we check during an MOT take a look at our post on What’s Checked in an MOT here.
It's also worth knowing what an advisory means if your car does pass. An advisory isn't a fail, but it's the tester flagging something that's likely to become one within the next twelve months. Treating advisories as a to-do list rather than ignoring them is the single easiest way to stop next year's test throwing up a nasty surprise.
And if a car does fail on our watch, the fix is usually more straightforward than people expect. Leave it with us and we can retest for free the next working day on most items. Take it away and bring it back within ten working days, and there may be a smaller partial retest fee instead of paying for a full test again.
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