Tips and Advice

How to spot a slow puncture and what to do if you have one

Ignoring a slow puncture can be dangerous and costly - these are our top tips for spotting and fixing them

How do you spot a slow puncture, and if you have one what should you do? Is it safe to just top up the pressure on a regular basis or should you have it attended to immediately? And what could be the cause of a slow puncture? In this article we explain all...

The tyres on your car are perhaps its most vital safety component; they might only have a small contact patch with the road but they’re literally keeping the car on it. Ensuring your car is equipped with good quality tyres that are in decent condition could well save someone’s life, so it’s vital to monitor the condition of the tyres on a regular basis. This is especially true these days, as extended service intervals means trips to the dealership for regular maintenance are few and far between.

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While we’re all aware of the requirements to have tyres with a decent tread depth – the legal minimum is 1.6mm in a continuous band around the central three-quarters of a tyre – we tend to pay less attention to the possibility that one or more of the tyres on our cars might have a slow puncture.

What are the visual signs of a slow puncture?

If you’ve recently passed your driving test, you will no doubt be familiar with the guidance in the Highway Code that you should give your car a visual inspection before you drive away, but many of us may have forgotten this good advice. Have a check around your car to see if any of the tyres appear to be of a different shape – do any of them look to be sagging under the weight of the car?

In extreme cases in which a tyre has been under-inflated for some time you may notice some sidewall damage to the tyre, with the maker’s name and tyre numbering becoming worn away where the sidewall of the tyre has been in contact with the road.

You can examine the tyre tread for anything that shouldn’t be there; screws, nails or other debris that’s become lodged in the tyre tread. If you do spot something like this, you’ll be faced with the conundrum of whether to remove it or not. There’s a chance that while the foreign object may have pierced the tread it hasn’t actually made it all the way through so removing it immediately will prevent any further damage. Conversely, it might actually be plugging the hole and keeping the tyre inflated - removing it will cause the tyre to deflate. If you do remove a foreign body from the tyre, try putting a few drops of water onto the damaged area – this will allow you to spot air bubbles escaping from the tyre so you can take immediate action and have the tyre repaired or replaced.

Spotting a slow puncture while driving

When you’re behind the wheel, turn off the radio and listen carefully for the telltale ticking noise that you will experience if there is a foreign body in the tyre tread – the noise will speed up and slow down with the pace of the car.

You may also notice a difference in the way the car handles. Does it tend to pull to one side or the other if you hold the steering wheel very lightly? Does the car always seem to want to pull in one direction when braking? Does the car’s road-holding seem affected or does it wallow when going over bumps? If you experience any of these then you should stop and inspect your tyres, or take it to a tyre dealer for a closer inspection.

Checking the pressures

With extended service intervals our cars tend to see the inside of a workshop less frequently so it’s worthwhile investing in a hand-held tyre pressure gauge or a foot pump with a gauge attached. They don’t tend to be very expensive and spotting one slow puncture before it becomes an issue could well save far more money than the purchase price of the gauge or pump. Checking the tyre pressures on a weekly basis is good practice and should take no more than a few minutes.

We’d advise against relying on the gauges found on petrol forecourts as they can be inaccurate and are frequently out of order. They have a hard life – they can be driven over and dropped by careless users – and ideally your tyre pressures should be checked when they’re cold. Tyres become hotter when you drive your car and the hot air inside the tyres can lead to inaccurate pressure readings.

If you have a car that was registered after 1 November 2012, or one that was produced before that date which has run-flat tyres, then your car will be equipped with a tyre pressure monitoring systems (TPMS) so you should get a warning from the car if it detects a tyre is low on pressure.

Can slow punctures be repaired?

Whether a slow puncture can be repaired or not will very much depend on what has caused the puncture and for how long it’s existed. The best course of action will be to take your car to a tyre specialist as soon as you become aware of the puncture. Driving on a punctured tyre for longer than is necessary could well be dangerous and may end up costing more money, as a tyre that’s been driven on in a semi-inflated state may not be repairable.

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If debris or a foreign object piercing the tread is the cause of the slow puncture, then the chances are that the tyre can be repaired. If the damage is right at the edge of the tread by the sidewall then it can’t be repaired.

However, if the tyre has been driven on in a deflated state for a period of time, the tyre dealer may refuse to repair it. Once the tyre has been removed from the wheel rim the tyre dealer will be able to assess whether the sidewall of the tyre has been weakene; if this is the case you will need to buy a new tyre.

One exception to the rule of puncture repairs to the tread is in the case of run-flat tyres. These tyres are designed to be driven on for a distance when ‘flat’ – usually 50-100 miles depending on manufacturer and the load in the vehicle – and as a result they have much stiffer sidewalls than normal tyres. This makes it almost impossible for a tyre dealer to know whether or not the structure of the tyre has been affected, so the majority of the major national chains will refuse to repair them.

If the tyre has sidewall damage, either from hitting a pothole, kerb, or from having some debris from the road lodged in it, then you will also need a new tyre as its structure will have been affected.

Slow punctures can, in some cases, be caused by a faulty tyre valve. If the valve dust cap has gone missing, dust and grit can get into the valve causing it to lose air. In this situation the tyre can be removed from the wheel rim and the faulty valve can be replaced.

It’s also possible that a slow puncture could be the result of a damaged wheel rim. On older cars with steel rims it’s possible that rust has built up on the wheel rim, which can lead to the tyre having a less than perfect seal where it joins the wheel rim. Similarly, a wheel rim that has been damaged by a kerb or pothole could cause a slow puncture. In the case of split rims fitted to some high-performance cars, there could be a leak where the parts of the wheel join together. In this situation you should have the wheel sent to a specialist for repair or source a new one.

In extreme cases it is also possible for the metal of the wheel to become porous over time, but this is very unusual and is most likely to occur with specialist magnesium wheels.

You might also be tempted to use a can of tyre sealant to cure a slow puncture but this isn’t recommended. Tyre sealant is generally a product used to temporarily repair a puncture when on the road or motorway, and isn’t recommended for permanent repairs. It’s also worth noting that once this type of sealant has been used it may make the tyre unrepairable so should really only be used in an emergency.

The best practice is to inspect the condition and pressure of your car’s tyres on a regular basis - once a week if possible. Ignoring a slow puncture can be dangerous as a partially inflated tyre will cause an imbalance to your car’s road-holding and braking performance. Driving on a tyre with a slow puncture can easily damage the tyre, meaning you will have to pay for a replacement rather than a repair.

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