Tyres are the only part of your car in contact with the road. That one fact makes tyre pressure and tread depth two of the most safety-critical checks you can perform. They take five minutes, require no mechanical knowledge, and are specifically assessed on the RSA driving test. Yet many learner drivers arrive on test day without ever having checked either.
Vehicle Safety & Pre-Drive Checks — Article Series
In This Guide
- Why Tyres Matter More Than People Realise
- Legal Tread Depth in Ireland
- Tread Depth Levels — Safe to Illegal
- How to Check Tread Depth
- The €1 Coin Test
- How to Check Tyre Pressure
- Where to Find the Correct Pressure
- Aquaplaning — What It Is and How Tyres Prevent It
- Other Tyre Damage to Look For
- Tyres and the RSA Driving Test
- How Often to Check
- Common Mistakes
- Frequently Asked Questions
Why Tyres Matter More Than People Realise
Your car's steering, braking, cornering and traction are all delivered through four tyre contact patches — each roughly the size of a hand. Every gram of grip, every braking force, every turning input passes through those tiny contact areas. When tyre pressure is wrong or tread is worn, those contact patches become less effective — and everything else suffers.
In wet Irish conditions — which are frequent — the difference between properly inflated tyres with good tread and worn, under-inflated tyres can mean the difference between stopping safely and aquaplaning into a collision.
Legal Tread Depth in Ireland
The RSA Rules of the Road sets out the minimum standards clearly:
- 1.6mm — the legal minimum tread depth in Ireland across the central three-quarters of the tread width. Driving below this is an offence.
- 3mm — the RSA strongly recommends replacing tyres at this point. Below 3mm, wet-weather grip deteriorates significantly.
The 1.6mm legal minimum applies across the main tread area around the entire circumference of the tyre. However, the RSA is explicit that reaching the legal minimum does not mean the tyre is safe in Irish road conditions — particularly in rain. A tyre at 1.6mm may be legal but it performs significantly worse in wet conditions than one at 3mm.
Tread Depth Levels — Safe to Illegal
~8mm
New tyre. Full grip. Ideal wet-weather performance.
4–8mm
Good condition. Normal safe driving range.
3mm
⚠ RSA recommends replacing. Wet grip beginning to reduce.
1.6mm
❌ Legal minimum. Replace immediately. Dangerous in wet conditions.
Below 1.6mm
Illegal. Offence to drive. Vehicle is unroadworthy.
How to Check Tread Depth — Step by Step
The most accurate method is a dedicated tread depth gauge, available from any motor factor or petrol station for a few euro. Insert the probe into the main tread groove, press down until the base is flat against the tyre surface, and read the measurement.
For front tyres, turn the steering wheel to full lock — this exposes more of the tyre and makes inserting the gauge easier. Check the rear tyres from behind the wheel arch.
The probe should enter the main groove at a 90° angle. Press the base flat against the tyre surface. Read the measurement from the gauge scale.
Tyres can wear unevenly — more on one side than the other, or in patches. Check at several points across the central three-quarters of the tread width and at different points around the tyre.
Each tyre wears at a different rate. Never check one and assume the rest are the same. If your car has a spare wheel, check it too — a flat spare is useless in an emergency.
The RSA recommends replacing at 3mm. A tyre at 1.6mm is technically legal but significantly compromised in wet conditions. Do not wait for the legal minimum — by then it is already borderline unsafe.
The €1 Coin Test
If you do not have a tread depth gauge to hand, a €1 coin provides a quick visual guide.
How to Check Tyre Pressure — Step by Step
Tyre pressure affects grip, fuel economy, tyre lifespan, and handling. Over-inflation reduces the tyre's contact patch and can make the car skittish. Under-inflation increases the contact patch too much, causes overheating and uneven wear, and can lead to a blowout.
Tyre pressure rises as the tyre heats up during driving. For an accurate reading, check before your first journey of the day or after the car has been parked for at least two hours. Never adjust cold readings based on a hot tyre measurement.
The correct pressure is in your owner's manual, on a sticker inside the driver's door frame, or inside the fuel filler flap. Note that front and rear tyres sometimes have different recommended pressures, and cars carrying heavy loads may require higher pressure.
Unscrew the small rubber or metal cap from the tyre valve (keep it safe — lose it and dirt gets in). Press the pressure gauge firmly onto the valve stem. Digital gauges are easiest to read accurately.
Pressure is measured in PSI (pounds per square inch) or bar. Most cars run between 28–36 PSI (1.9–2.5 bar). Compare the reading to the manufacturer's specification for your vehicle and load conditions.
If too low — add air using a pump or petrol station air machine. If too high — press the small pin inside the valve to release air in short bursts, checking frequently. Re-check after adjusting.
Never assume all tyres are the same — check each individually. Replace the valve cap after each tyre. Finish by checking the spare tyre if your car has one.
Pre-drive checks covered in your first EDT lesson
BP Driving School covers tyre checks, oil, lights, wipers and the full pre-drive routine — RSA-approved, North Dublin, 7 days a week.
Where to Find the Correct Tyre Pressure
| Location | What to Look For |
|---|---|
| Driver's door frame sticker | Most reliable — usually shows front and rear pressures for normal load and full load |
| Fuel filler flap | Some cars place the sticker here instead of the door |
| Owner's manual / glove box | Complete pressure specifications including spare tyre |
| Tyre sidewall | Shows the maximum pressure the tyre can hold — NOT the recommended driving pressure. Do not use this figure. |
Aquaplaning — What It Is and How Tyres Prevent It
Aquaplaning (also called hydroplaning) is a condition where a wedge of water builds up in front of a tyre faster than the tread can channel it away. When this happens, the tyre loses contact with the road surface entirely — the car is effectively skimming on a film of water with no grip, no steering and no braking.
It typically occurs at higher speeds in heavy rain. The driver may feel the steering suddenly become very light, the car drifting, or hear a change in road noise. The correct response is to ease off the accelerator gently — do not brake or steer sharply — and allow the tyres to regain contact with the road.
Other Tyre Damage to Look For
Tread depth and pressure are the two main checks, but also visually inspect each tyre for:
- Bulges or lumps — a bubble on the sidewall indicates internal structural damage. Replace immediately — a bulge can fail without warning at speed
- Cuts or gouges — particularly on the sidewall, which is thinner and not covered by the tread depth requirement
- Embedded objects — screws, nails or stones lodged in the tread. Do not remove them yourself without a spare ready — removal can cause rapid deflation
- Uneven wear patterns — wear on one edge only (wheel alignment issue), wear in the centre only (over-inflation), or wear on both edges (under-inflation)
- Cracking — small cracks across the tread or sidewall can indicate age degradation, particularly on older tyres with low mileage
Tyres and the RSA Driving Test
The RSA examiner assesses tyre condition as part of the technical checks at the start of your driving test. You must be able to explain and demonstrate how to check tyre pressure and tread depth, and your test vehicle's tyres must be in a roadworthy condition.
- Air pressure — correct for the vehicle
- Tread depth — at or above the legal minimum
- Tyre condition — no visible damage, bulges or cuts
When the examiner asks you about tyres, they want to hear that you know:
- The legal minimum tread depth is 1.6mm
- The RSA recommends replacing at 3mm
- Pressure should match the manufacturer's specification (not the tyre sidewall maximum)
- Tyres should be checked cold
- The spare tyre should also be checked
How Often Should You Check Your Tyres?
A sensible routine for Irish drivers:
- Tyre pressure — every two weeks and before any long journey
- Tread depth — monthly and before the winter months when road conditions worsen
- Visual damage check — every time you walk past the car before getting in
- Before your driving test — the day before, not the morning of
- After any kerb strike or pothole impact — check for sidewall bulges immediately
Common Mistakes
Using the maximum pressure number on the tyre sidewall
The number on the tyre sidewall is the maximum safe pressure the tyre can hold — not your recommended driving pressure. Using it can over-inflate tyres, reducing grip and causing harsh ride. Always use the manufacturer's specification.
Checking only one tyre and assuming the rest are the same
Tyres wear at different rates depending on position, alignment and driving style. Front tyres typically wear faster than rear tyres. Always check all four individually.
Checking pressure when tyres are hot
Driving heats the air inside the tyre, expanding it and raising pressure by several PSI. A reading taken after driving is inaccurate. Always check cold.
Waiting until a tyre visibly looks flat
A tyre can be 10–15 PSI under the recommended pressure and still look normal to the eye. Under-inflation is often invisible. Use a gauge regularly — do not rely on visual checks alone.
Ignoring uneven wear
Wear heavier on one side, or only in the centre, usually points to wheel alignment or inflation issues. These problems accelerate tyre wear and affect handling. Have alignment checked if wear is uneven.
Forgetting the spare tyre
Many drivers check all four tyres but forget the spare. An under-inflated spare is useless in a roadside emergency. Check it as part of your regular routine.
Frequently Asked Questions
More from the Vehicle Safety & Pre-Drive Checks series
Your first lesson with BP Driving School covers tyre pressure, tread depth, and all other pre-drive checks — exactly as the RSA requires. Book your EDT course — RSA-approved, Swords, door-to-door pickup across North Dublin.
Already done EDT? Book a mock test and practise the technical check questions the examiner will ask on test day.