Motorcycle MOT Preparation — What Fails Bikes and How to Avoid It

The motorcycle MOT is the legal safety inspection you need every year once your bike is three years old. About 30% of motorcycles fail their first attempt — and the failures are almost always preventable.

This guide is what the actual MOT testers look for, in the order they check, with what you can do to pre-empt each one.

What the MOT actually tests

The motorcycle MOT covers:

1. Lights — headlight (high + low), front position, rear, brake, indicators, number plate light
2. Steering and suspension — head bearings, fork condition, swingarm play
3. Brakes — discs, pads, fluid, callipers, hoses, master cylinders
4. Wheels and tyres — tread depth, sidewall condition, wheel bearings, rim damage
5. Frame and structure — corrosion, cracks, alignment
6. Exhaust and emissions — security, leaks, noise (subjective), emissions (post-2017 bikes)
7. Throttle and clutch operation — smoothness, return
8. Number plate, VIN, rider controls — present, legible, working

It does NOT test:

• Engine performance, fuel economy, gearbox
• Service history or maintenance condition
• Anything aesthetic (paint, fairings)
• Suspension preload, ride height, riding position

The top 10 failure causes (and the fix)

In rough order of frequency:

1. Faulty / dim / misaligned headlight

Why it fails: bulb dim, headlight aim too high (dazzling oncoming) or too low (no useful range). Fix: new bulb (£5–25). Check aim against a wall at 5 m — main beam horizontal centre should be at headlight height.

2. Worn tyres

Why it fails: tread depth below 1 mm continuously across ¾ of the tread width, or any visible cord. Also: damage to sidewall, uneven wear. Fix: new tyres (£100–250 fitted). Date code on sidewall: anything older than 5 years should be replaced regardless of tread.

3. Worn brake pads

Why it fails: pads worn below minimum thickness, or the contact pattern on the disc shows uneven wear. Fix: new pads (£30–60 fitted). While you’re there, check discs for minimum thickness — usually stamped on the disc itself.

4. Brake fluid contaminated or low

Why it fails: fluid dark / black, or below minimum mark. Modern bikes are picky about this. Fix: brake fluid bleed and replacement (£40–80). Should be done every two years regardless.

5. Steering head bearings notchy

Why it fails: detectable notch when bars are turned through centre. Fork wobble at speed. Fix: new bearings (£150–250 fitted). On older bikes this is sometimes a simple regrease.

6. Fork seal leak

Why it fails: visible oil residue on fork stanchions, oil running down legs. Fix: new fork seals (£150–300 fitted). Sometimes you can clean the seal with a fork-seal scraper as a temporary measure but plan to fix properly.

7. Chain too loose or too tight

Why it fails: chain slack outside manufacturer spec (consult your service book), or visible damage to sprockets. Fix: adjust chain (free if you have tools, £20 if you don’t). If chain is worn AT ALL, replace chain AND both sprockets together.

8. Indicator / brake light not working

Why it fails: any bulb out, or LED indicator unit failed. Fix: new bulb (£3–10) or new LED unit (£20–60).

9. Exhaust system leak or insecure

Why it fails: audible leak at the headers/cylinder head joint, or downpipe loose on its mounting. Fix: new exhaust gasket (£10–30) and tighten / replace fasteners. Header studs corrode — if you’re snapping them, the labour cost jumps.

10. VIN or number plate not legible

Why it fails: VIN obscured by aftermarket parts, number plate cracked, peeling, or non-compliant typeface. Fix: clean / repair / replace plate (£10–25). Replacement plates from any number plate shop with V5C as proof of ownership.

The 30-minute pre-MOT check

Do this the day before your test:

1. Walk around the bike with the engine off. Check every light works (headlight high+low, indicators all four, brake light at both pedal and lever, number plate light). Brake light should come on with EITHER brake.
2. Check tyre tread depth. A 20p coin: if the outer band is hidden, you have at least 1 mm of tread.
3. Check brake pads. Look through the callipers. At least 3 mm of pad material.
4. Check chain tension. Measure the slack in the middle of the bottom run — should be within service manual spec (usually 25–35 mm).
5. Check brake fluid level + colour. Top up if needed. If dark, plan a flush.
6. Bounce-test the suspension. Push down on the front, let it rebound — should be one clean bounce, not multiple.
7. Look for fork seal leaks. Wipe stanchions, look for oil.
8. Pump tyres to manufacturer pressure. Cold pressures, before you ride to the test.

Most failures get caught at this 30-minute check. The ones that don’t (head bearings, ECU faults, internal brake issues) are usually known to the owner already.

Where TH Motors fits

Every bike at TH Motors is supplied with a minimum of 6 months MOT remaining. We do the pre-sale MOT or have it freshly done before the bike reaches the showroom — so your first 6 months of ownership has the MOT taken care of.

If you’re shopping with the next MOT in mind, our showroom listing shows the bike’s current MOT status. Call to discuss any specific bike.

The honest summary

The MOT failure rate is high mostly because owners don’t do a 30-minute pre-check. Spending an hour the day before saves £45 (re-test fee) and a follow-up appointment.

The cheap fixes (bulbs, pads, fluid, chain adjustment) account for over half of all failures. The expensive ones (head bearings, fork seals, brake hoses) you usually know about already because the bike rides differently.

Catch the cheap ones in advance and the test is straightforward.