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Sometimes flats are caused by more unusual items, as this list of strange things found in tires demonstrates.

Flat tires are one of the most common car problems, but the fact that they happen pretty frequently doesn’t make them any less annoying! In the United States, seven tires puncture every second adding up to an eye-watering 220 million flat tires every year. On average, motorists will experience five flat tires in their lifetime.

That is why learning to change a tire is one of the most important skills any motorist can learn – and luckily, it is also one of the most straightforward, needing just a few tools and not as much brute strength as you might imagine. Motorists can save themselves a lot of money and a lot of embarrassment by learning this basic repair for themselves, rather than calling out the AAA for something so straightforward.

There are lots of reasons why tires can go flat or get a puncture, from over-filling with air to problems with a leaking valve. However, by far the most common cause is a sharp object in the road, which pierces the rubber, sometimes causing a slow leak of air, but in more dramatic cases, instigating a tire blowout – a potentially dangerous state of affairs which can easily lead to the driver losing control of their vehicle.

Punctures from nails, screws, and bits of broken glass are ten a penny, but sometimes flats are caused by more unusual items, as this list of strange things found in tires demonstrates.

“Find a penny, pick it up, and all day long you’ll have good luck.” So goes the old saying about finding coins lying on the sidewalk, but coins lying on the road can be anything but good luck for motorists. You might not think that coins, with their harmless-looking round edges, would be able to do much damage to the thick rubber on car tires, but one motorist found out the hard way that this simply isn’t true. They took their tire to a local repair shop after it was afflicted by a mystery puncture, and the mechanics found a quarter buried deep in the tire’s surface.

If the motorist who found a dog’s tooth embedded in his car’s tire was shocked, then the car owner who discovered that his puncture was caused by the rubber wheel from a child’s stroller must have been completely bemused. How does something with completely round edges even cause a flat tire in the first place? The car wheel must have hit the stray stroller wheel at just the wrong angle, for it to embed itself in the surface of the rubber breaking it apart and causing a slow puncture – although, given the size of stroller wheels, the chances are the driver would have felt its presence, long before they noticed the tire deflating!

You might think that it’s only motorists living in the less than salubrious parts of our toughest cities that might have to worry about getting a flat tire from a stray bullet – but bullets don’t have to be moving for them to damage a car’s wheels and cause a puncture.

Drive around any areas where hunting takes place and you may see the odd spent bullet lying by the roadside.

When those bullets roll onto the carriageway, they can easily wedge themselves into the tread on the rubber, starting a slow puncture – and costing the owner a new tire in the end!

Punctures don’t always happen when your car is speeding down the highway, and a flat tire isn’t always someone else’s fault. One motorist who discovered one of his tires was going flat soon found that the cause was a quarter-inch wrench which had managed to embed itself into the rubber. What’s worse, he soon realized that the wrench was actually his own and that the damage must have been caused when he drove it in his own garage or perhaps on his driveway. Not only did this driver have to pay for a new tire, but he also had to buy a new wrench to make sure his set was complete.

This next strange item didn’t just cause a slow puncture, it actually managed to rip most of the rubber in the tire to shreds in a very short time. How or why a steak knife was lying on the road is a question for another time – and perhaps even for the local police – but the drive of this car was very unlucky to get such an item wedged into the surface of their tire accidentally. Or was it an accident? After all, steak knives seem to be a common weapon of choice for people who have decided to slash tires as some sort of revenge scheme.

Like the motorists whose tires have been destroyed by steak knives, there is a reasonable chance that the car owner who discovered one of these buried in his tire was the victim of a deliberate attack.

At the same time, these things do get thrown away in the trash every day, and the offending item could easily have been accidentally picked up.

Either way, the sharp razor blade made mincemeat of the tire’s rubber, wedging itself into a gap in the tread, and creating a large and unfixable hole. The driver had no choice but to splash the cash on a whole new tire.

Naturally, if your car is unlucky enough to be caught in the middle of an actual blast, then the shrapnel that ends up buried in your tires is going to be the least of your worries!

However, there is a surprisingly large amount of bomb shrapnel still lying around on the roadside in Europe or other areas where there have been relatively recent conflicts.

People are still finding unexploded bombs in parts of Europe, which can be unstable and extremely dangerous, so maybe a piece of stray historic shrapnel causing a puncture is not that serious an issue, in the grand scheme of things.

Every home has a collection of those old and misshapen wire coat hangers - the kind that are of no use anymore for hanging clothes - and most people don’t ever remember where they came from. Sometimes, these poor unwanted wire hangers get thrown in the trash or recycled, and sometimes they end up by the side of the road, lying in wait for an innocent motorist to pass by. Yes, amazingly one driver managed to get a puncture when the hook part of the hanger penetrated the rubber of his tire, leaving him dragging the rest of the hanger noisily along the road.

Like the quarter-inch wrench earlier in the list, this was another strange item found in a tire which was probably more likely to have been picked up in a home workshop. You may find drill bits on the roadside, but they are more likely to have dropped off the shelves where the tools are kept in your garage. Still, given that drill bits are generally quite dull – it is the power of the drill itself, after all, which forces them to break through tough surfaces – the motorist whose flat tire was caused by a stray drill bit was very unlucky.

Dogs are notorious for chasing things, cats, other dogs and, of course, cars. They do seem particularly interested in car tires, enjoying snapping and biting at them, whether the car is in motion or parked up minding its own business.

Hundreds of people have come back to their vehicles to find a mysterious puncture, only for it to eventually be established that a neighborhood pooch was responsible.

In one such case, however, it was much easier for the owner of the car to identify the culprit, as the dog had left one of its teeth behind, embedded in the rubber surface of the tire.

Anyone who has ever had close contact with deer antlers will probably not be too surprised to find out that they can cause a flat tire. These tough appendages are, after all, designed to be used in combat with other stags, so they have to be pretty tough – and they often have those intimidating-looking sharp points and edges. Nevertheless, when one motorist decided to investigate why one of his tires appeared to be deflating, I expect a piece of deer antler was still one of the very last things he was expecting to see protruding from the rubber tread of his wheel.

Some drivers might have ended up with flat tires after colliding with a deer somewhere out in the country, but the motorist who found a pedal cycle stuck in the rubber surface of his wheel must have also had a moment of doubt, trying to remember if he had hit a cyclist and not even noticed! It’s more likely, however, that the pedal had worked its way loose to lie by the side of the road, and the poor driver who ended up with an expensive flat tire was just driving in the wrong place, in the wrong way and at the wrong time.

While most car punctures are caused by man-made materials – glass, nails, screws and other tools – it does seem that there are plenty of corners of the natural world which have it in for our tires. We have already seen how twigs, mesquite thorns and even deer antlers have managed to puncture car tires, but who would have guessed that porcupine quills were also sharp enough (and strong enough) to pierce their way through the thick, tough rubber on our wheels? Each porcupine quill has up to 800 barbs on the first 4mm of the tip, with backward facing hooks which make the quills difficult to remove without causing more damage.

A word of caution here is to be careful where you drop your house keys around your car, as there have been several cases where these innocent-looking items have actually managed to cause a flat tire.

It may seem impossible – after all, keys should lie flat on the floor – but they can easily get kicked up off the driveway by your front tires, which then force them at speed into the rubber of your rear wheels.

Keys could also be used to deliberately puncture tires, but you’d need to use a fair amount of elbow grease to force a key into the rubber, so it is more likely to be an unlikely accident.

It seems somehow unfair that so many of our tools can end up actually damaging our car tires. Most people spend a lot of money to buy good-quality tools that are going to keep their car running well, not to put it out of action. If there is one tool that looks almost as though it was designed to cause punctures, however, then that would have to be the old-fashioned claw hammer. That tough claw end is more than strong enough to embed itself in the rubber, and cause the tire to deflate – although you would notice that there was a hammer stuck in your tire long before you noticed that the wheel had gone flat!

Most people carry disposable pens around in their pockets or in their purses – and many of those pens end up dropped on the floor. They might look unattractive, but no-one would think that those cheap, throwaway pens would pose any kind of hazard to passing traffic. And yet a few motorists who have noticed that one of their tires appears to be deflating have taken their car to the repair shop or inspected it themselves to find that the inner part of the pen, the metal tip and the plastic tube of ink, has actually managed to pierce the rubber, and cause a slow puncture.

Spark plugs are an essential component of a car’s engine, creating the spark of electricity which is needed to create the ignition and start the car’s combustion engine. Replacing them is also one of the easiest car repair jobs, so many people just end up doing the swap themselves.

It is somewhat ironic, therefore, that one motorist ended up with a slow puncture as a result of old spark plugs being dropped on the floor of their home garage.

Spark plugs aren’t particularly sharp, so the car must have to have been driven over it in a very particular way for it to end up puncturing the tire.

The items on this list so far might be strange things to find in your tire but they could, in theory, end up in anyone’s car tires, anywhere in the world.

However, there are some threats to car tires which are very geographically specific, and the thorns on the mesquite plant are one of those.

These particularly sharp and tough thorns pose quite a threat to tires in areas where it grows, in northern parts of Mexico and across the border into Texas, California, Utah and even as far as Kansas. Thorns can grow up to three inches in length, which explains why they find it so easy to puncture tires.

It may be a mystery as to how steak knives or razor blades ended up in someone’s tires, but at least there is no mystery as to how these tough and sharp items managed to cause so much damage. Yet sometimes, tires can end up just as ripped to shreds by something which seems perfectly innocent as they can by items which are more obviously damaging. One motorist who noticed that his car had developed a flat tire was astonished to find out that his puncture had been caused by nothing more sinister than a piece of wood – and not a piece that was particularly long or sharp at that.

Sources: driversedguru.com, evanstire.com, Toyota-4runner.org, bbc.co.uk, autoexpress.co.uk