If you're a motorist and you've never had a flat tyre, or a tyre that consistently loses pressure over time, don't feel left out: it's probably only a matter of time. Flat or damaged tyres are one of the most frequent cause of roadside breakdowns. Only flat batteries and alternator issues are more common.
Considering how common they are, it is surprising how vague many of us are about what emergency measures our car has to deal with such an occurrence, and about what we can and should do if it happens. Below is our effort to answer all those flat tyre questions you never knew you wanted to ask.
What causes flats, blowouts and deflation?
It seems like a daft question. It's understandable to assume that it's simply the result of driving over nails, broken glass or those 'stinger' spike things that the police use to stop stubborn people from trying to evade pursuit (not that we're implying anything. In reality, there is a whole list of things that can contribute to a blowout or unexpected loss of tyre pressure.
- Underinflation If tyres are underinflated, they can become unseated from the wheel rim. As the profile of an underinflated tyre is different from that of a correctly inflated tyre, areas that are not designed to make contact with the road may do so and sustain damage. Low tyre pressure can also affect steering response
- Overinflation Too much pressure in tyres places stress on the whole structure. In addition to reduced steering control, overinflation can exert enough pressure to cause a blowout, especially in very hot weather and/or at high speeds, when the air heats up and expands.
- Overloading Overloading can duplicate the adverse effects of both over and underinflation. Additional load weight compresses the air in tyres and increases the pressure. At the same time, it can force the tyre's profile to change and increase the chance of damage to areas that weren't intended to contact the road surface.
- Wear and tear Things wear out. Things that are exposed to load and friction wear out relatively quickly. It's important to check your tyres regularly and to ask your mechanic to do so when they carry out your service or MOT (they will do so anyway, but mentioning it reminds them to alert you to early warning signs, even if things aren't yet serious).
- Accidental damage Potholes seem to be everywhere. It will come as no surprise to hear that they take a heavy toll on tyres. Driving over rough or sharp surfaces will obviously cause damage, and bumping kerbs, especially at speed, can cause catastrophic damage to a tyre, even a blowout.
- Faulty or damaged valves Occasionally valves can be defective or incorrectly installed. Even when that's not the problem, valves can be damaged by impacts or snagging. One of the biggest culprits, however, is dirt which can jam the valve. If you lose a dust cap from a tyre valve, pop into your local automotive store, or even a supermarket: they are easy to replace.
- Exposure to solvents and corrosives Modern tyres aren't as susceptible to damage from oil and other petroleum products as older rubber formulations were. However, there is a range of chemicals that will cause damage ranging from stripping protective coatings to serious structural damage. Don't park in puddles of unidentified stuff, and give your tyres a good clean when you wash the car.
- UV exposure Not as big an issue in the cloudy UK as it is in some countries, but UV will damage most things given time. Long term exposure can cause drying and cracking to the rubber in tyres. Keeping your car out of prolonged exposure to the sun can only help.
How do I cope with a blowout when driving?
- Don't just hit the brakes Prioritise control over stopping. Keep a firm grip on the wheel and as soon as it is safe to do so, guide the car off the carriageway, as far as it is possible to do so. Only brake when you are confident in your control of the vehicle and when the speed is below 40mph. Sudden or hard braking at high speed, especially with a damaged tyre, can be dangerous.
- Be aware of other vehicles One of the reasons for not braking reflexively is the possibility of stopping in a sudden or uncontrolled manner directly in the path of an oncoming vehicle.
- Hit the hazard light switch But only if and when you can do so without sacrificing control or awareness.
- Check the road for debris from your blowout Substantial debris is a bigger problem for large vehicles, but even a car tyre can make a mess if it bursts. Only if the road is not busy and you can clearly see both ways, then you may decide to remove large pieces of debris from the path of other vehicles. If the road is busy, or you do not have a clear view in both directions, stay off the carriageway and call the police to report the hazard.
- Repair/replace the damaged tyre, or prepare to proceed if you have run-flat tyres The number of cars supplied with full spare wheels and tyres is rapidly shrinking. These days it is common for cars to come with run-flat tyres or emergency repair kits. If your car has one of these measures, then check to ensure you can work safely before implementing those measures.
- If you have any doubts, phone for roadside assistance If you are not confident that it is safe for you to inspect or attempt to repair the tyre, or if you do not have any means of doing so, then call your breakdown service. If you are not a member of a breakdown service, this would be a great time to join. They'll be happy to sign you up at the roadside.
What measures does my car have to deal with a flat tyre?
Again, it can sound like a daft question, but many people don't think to check until something inconvenient happens. It's obvious for those of us who drive 4x4's with clearly visible rear-mounted spares, but for many cars it can be far from obvious what you're supposed to do.
Our first suggestion is, of course, RTFM: yes, "read the fabulous manual" . Unless you've lost it, your car should have one. It's the book shaped thing that usually comes in its own little folder.
Manual or no manual, cars usually come with one or more of the following.
- Spare wheel and tyre A spare can be full-size, or an annoying, reduced-width version known as a "space-saver". The spare wheel can be mounted conspicuously on the rear of the vehicle (Hooray!) or hidden away in a well in the boot. On some cars, the spare might be annoyingly concealed with an external bracket on the underside of the car (Boo!), in which case it is usually released by a bolt or nut in the boot. Space-saver tyres are for getting you out of trouble and to a tyre centre or mechanic. They're not intended to be used for driving long distances.
- Run flat tyres Some manufacturers use 'run-flat' tyres which, as the name suggests, can be driven on even when punctured. That doesn't mean that you can drive on them as normal, but they should see you safely to a tyre dealer or mechanic. Amongst those who use run-flats are Mercedes, Mini, Audi and BMW.
- Emergency kit with sealant and inflator The kit usually consists of a sealant and a compressor. It takes up less space than a spare wheel and is much lighter. It is, of course, also cheaper for the car manufacturer to supply. Emergency kits have become very common. In fact, it is reported that only 3% of new cars actually come with spare wheels now. Like most other measures short of a full spare wheel and tyre, the emergency kit is a temporary fix that is only intended to get you as far as a tyre centre or garage.
How do I change a wheel?
- Check that you are in a safe location to work on your car.
- Check that you actually do have a spare and the tools to change the wheel. The jack and wrench are usually in the boot of the car.
- Apply the handbrake and get everyone out of the car.
- Position wheel chocks if you have them or can find something to serve that purpose (bricks, rocks, wooden blocks). It is a wise safety precaution that stops the car from rolling while jacked up.
- Loosen the wheel nuts on the wheel with the flat before jacking up the car. You may need to remove wheel trim to get to the wheel nuts. Don't remove the nuts completely just yet.
- Jack the car up. Make sure you position the jack as shown in your car's manual. There will be special jacking points that are strong enough to support the car's weight. Putting the jack in the wrong spot can damage the car. Raise the car so the tyre is about 10cm off the ground.
- Remove the wheel nuts and lift/pull off the wheel then put it flat on the ground so it can't roll.
- Mount the spare wheel and put the wheel nuts back on, tightening them just by hand. Make sure the wheel is pushed right back on the threaded studs and the nuts are snug.
- Lower the car so the tyre is touching the ground and then firmly tighten all the wheel nuts with the wrench.
- Lower the jack the rest of the way and remove it, then do a final check to ensure all the wheel nuts are tight.
- Remove the chocks if you have used them.
- Check the pressure of the tyre you just fitted.
- Stow the wheel with the punctured tyre, and all the tools and other items back in your car.
- Take your flat tyre for professional repair or replacement. If your tyre is a space-saver, do not drive further on it than you need to in order to get the full-sized wheel repaired.
How do I use an emergency repair kit?
Usually, you put the sealant inside the tyre, use the compressor to inflate the tyre and then drive a certain distance to distribute the sealant. You then check the tyre before driving to get a professional repair or replacement.
Detailed instructions for use may vary significantly between kits. Fortunately, kits come with instructions that will tell you how to use the one you have.
