What can you say about a spare tire*? It's spare. Redundant. Not needed. Until you have a flat. Then you jack up the car, find a large wrench, summon the necessary brute strength to undo the torque nuts on the wheel (try not to strain your back) and swap the tires over, remembering to keep your hands and clothes clean and to tighten the nuts properly after fixing the thing.

*The Brits spell this word tyre, and that's what I'm going to do.

Except most people don't. Industry data shows that 75 percent of people won't change a tyre by themselves. They'd rather call the roadside rescue. Or phone a friend, or partially inflate it and drive to the nearest tyre depot to get it fixed. Or they use some kind of spray-in Fix-A-Flat type gunk.

Besides, who wants to spend an hour by the roadside trying to change a tyre when there are rapists and muggers on the loose? Or when it's raining.

Furthermore, Police statistics show that roadside repair is one of the best ways to shuffle off this mortal coil. Trucks and other vehicles often wander from the main carriageway. Who wants to be standing, or crouching a couple of feet from the edge of a carriageway when trucks are thundering past at 80 km/h? Especially when those trucks can wander a few feet either way.

So the spare tyre really is redundant, right? Since we don't ever change the tyre over, why carry a spare. After all, who carries a spare fan belt? If that breaks, the car is immobilised, and it's a heck of a lot smaller and lighter than a spare tyre, but we don't carry one, because we never carried them. Which other car part goes wrong so often that we need to carry a spare and have the skills and tools to replace it?

Light bulbs. In France, and quite possibly elsewhere, you get fined if a cop catches you without a spare set of light bulbs, or with a defective light. Your brake light goes, you have to replace it. There and then. No excuses.

But a big heavy tyre? It goes back to the early days of motoring in Europe, when tyres were no larger or more effective than bicycle tyres. You carried three or four on each journey, as punctures and flats were a routine part of any journey.

Today's tyres and wheels are bigger, heavier and bulkier than they were in the 1920s. In fact, most cars today don't even have a proper spare. They have skinny spares. Half the width of a standard tyre and with a much lower speed rating. They save a lot of space and weight, which means money.

Just think, you drove your Ferrari with the beautiful white leather seats up the freeway and got a flat. You have the strength and the time and the courage to swap over the wheels, but find that the spare is skinnier than the blonde who should be sitting at your side. Where do you put the punctured tyre and its $1000 alloy rim?

On the passenger seat? I don't think so. Dirty, oily rubber and white leather don't mix.

So, like 75 percent of all motorists faced with a flat tyre, you call out the repair service, or you call a friend, or you break out the fix-a-flat. Anything but swap over the tyres.

Faced with this scenario, the tyre makers tried to find a way to keep cars mobile, even when they have a flat.

There are, today over half a dozen different solutions for drivers who want to keep going even when they get a flat tyre.

  • Compressor and sealant system
  • Tyre sealants
  • Reinforced sidewall tyres (for small cars, or low profile tyres)
  • Support ring (for SUVs or large, heavy cars)
  • Tweel type solution
  • PAX
  • Reservoir of air in the wheel

None is especially expensive, but almost all of them rely on some kind of technology to inform the driver and the vehicle electronics when the pressure falls below some critical level.

The exception to this rule is the Tweel or Airless idea promoted by Michelin. This relies on mechanical supports to replace the pneumatic support within a tyre. A conventional tyre works by using air pressure to keep a toroidal envelope inflated and relatively rigid.

About five years ago -- in 2000-ish Michelin asked two teams of engineers to develop tyres that did not need air pressure. Both sides came up with similar solutions. Each has a circular tread made of conventional tread rubber, but the method of linking this to the wheel was different.

The team on the US side of the Atlantic came up with the Tweel, which has a series of "spokes" made from flexible polyurethane. The spokes are not just wires, but plates, or vanes which can deform as the wheel meets an obstacle. At present, the idea is being used on low-speed applications such as wheelchairs and skid-steer loaders, but the company may well put a Tweel onto a car in the future.

The European team came up with the Airless. This is somewhat similar, but uses curved springs made from polyurethane to transit loads from the road to the wheel (and vice versa).

These two rather innovative ideas aside, the main solutions to extended mobility in the tyre industry require a system to measure pressure within the four road wheels, and then alert the driver to impending problems.

See also flat tire for more information on this

How to fit the spare tyre

Just in case you do need to replace a tyre with the spare, here is a step-by-step guide to doing the task. In theory it can be done in 15 minutes or so. I have done it in that time. It's not especially enjoyable and it is hard, physical work, but it can be done. Just.

Try to do this in a place where no cars or trucks are likely to sideswipe you. Ideally on a driveway. If not, then move as far away from fast traffic as possible. You can drive for a few hundred metres on a flat tyre, but only at a slow speed: walking pace. Anything faster is going to create so much rubbing friction inside the tyre that it will quickly destroy itself. If you have alloy rims, then go even slower and do not, under any circumstances, drive through pot holes or up kerbs. That will almost certainly crack the rim, setting you back another $200 - $300. Steel rims are a little more forgiving (and cheaper), but still, treat them with respect.

As you stop the car, switch the engine off and put it in Park (for automatics) or into first gear for stick shifts. Apply the hand brake (parking brake). The aim is to stop it rolling away, even on level ground.

Before you begin, it is best to ensure the spare is fully inflated and street-legal. In real-life, the spare is only likely to be checked once a year at the car's annual service. But you should be checking it every month or so. Besides, if you have checked the pressure and tread depth on the spare recently, then you will know where to find the spare when you need it. Usually it is in the trunk/boot. Though in some cars it is slung underneath that area on a wire carrying frame. If you empty the trunk and still do not see it, then try to pull up any flaps or carpeting in the trunk. You'll probably find it in there somewhere.

There should be some tools alongside the spare: a jack (to raise the car enough to get the wheel off the ground); a large spanner (called a wheelbrace or tire iron and shaped like a large cross), which is used to loosen the nuts and then tighten them again.

Take the spare wheel, the jack and the wheelbrace out of the car, but don't yet replace all the junk you had to remove to get at them unless it is raining. You are gong to have to put the hardware away again in a few minutes.

Next, locate the flat tyre. Find four bricks or stones and place them like chocks, one on each side of each of the two wheels on the opposite side from the flat. These will stop the car running away while it is on the jack.

Then, locate the jacking point. There is usually one on each side of the car, somewhere between the two wheels. If you have the owner's manual, that will show you exactly where to put the jack. Use the jacking point on the same side as the flat tyre. Doing it anywhere else runs the risk of bending metal and having the car collapse on you.

Next, go to the flat tyre and find the lug nuts that hold the wheel on. There are usually either four or five of them in a pattern around the centre of the wheel. With steel wheels there is often a plastic cover or hubcap that hides the lugnuts. This clips over the wheel and can be prised off with a screwdriver or similar.

N-Wing says The toolkit that comes with the car often has something you can use to lever the hubcaps off with.

On alloy wheels one of the lugnuts is often a locking nut to prevent theft. Usually there is a box in the car's glove compartment that contains a special nut which matches the geometry of the locking nut.

Don't jack the car up yet.

The next thing is to try and undo the (non-locking) lugnuts. They are held on tightly. It will be a struggle to undo them. If you try to undo them while the car is jacked up, the wheels may spin, making your task even more difficult, so leave the car on the ground where you can apply as much torque as possible.

Get the wheelbrace, place one of the spanner ends over one of the nuts and try to turn the brace counter-clockwise (to undo). If you can do that, it's all good. Loosen the nut until it is just a few turns away from completely off the threaded stud.

If not, then try to get some more leverage on the wheelbrace. Push down on one side of the X-shaped tool, and pull up on the other. If that doesn't work, you could try to use your weight to move the nuts: step on one arm of the wheelbrace and gradually apply more weight. If that doesn't shift it, then try pumping the wheelbrace with your foot, applying pulses of pressure until the lugnut loosens.

rootbeer277 says I find that putting the wrench horizontal to the ground and heaving up with all your might will either get the nut loose or give you a hernia. This way you can apply strength from your legs.

Sometimes a piece of pipe placed over the ends of the wheelbrace can extend the leverage enough to undo the nuts. If you have some oil, especially penetrating oil, you could try applying that to the nuts to reduce the friction.

rootbeer277 says Never put a pipe over the wrench to get more leverage, the wrench is only intended to handle so much torque, putting a pipe over it lets you apply more torque than it was built to stand.

I respond. True, that, where tightening the nut is concerned. Not for loosening, though. The nut will loosen at some level of torque. You can apply that through a small force at a large distance, or a hernia-inducing force at a small distance. So long as the tire iron will take enough torque to loosen the nuts, it matters not how much leverage you use. The nut should loosen before the tire iron breaks, or the thread strips or anything else nasty happens.

With some blood sweat and tears (and possibly a bit of outside help) loosen all the nuts on the wheel, including the locking one to the point where you can spin them with your fingers.

Now start jacking the car up. But before you do, a safety warning: The jack is not safe for working underneath the car. Cars move; jacks wobble. If you value any part of your anatomy, do not place it between the car and the road. Cars are heavy. If it comes off the jack, any anatomical parts impeding the downward motion of the car will be crushed.

rootbeer277 says In some cases, the jack will use the lug wrench to operate the jack. Might want to mention that in case someone gets confused that he's got a wrench but no jack handle.

There are two types of jack: the screw type and the hydraulic type. Both have a flat bit that goes on the ground and a shaped piece that pushes the car upwards. Put the jack directly under the jacking point and wind it up, until there is only a few millimetres' clearance. Now make sure everything is aligned properly and start raising the car. It will be hard, sustained work, but not as hard as loosening the lug nuts.

As you raise the car, keep checking that everything is aligned and that the jack is flat on the ground. If it starts leaning over, you must immediately lower the car and start again, or risk having the car fall down when it is without a wheel.

Lift the car until the flat tyre is only just clear of the ground. Lifting it higher means more work, and more hard lifting when you try to get the spare wheel on the car.

If, at this stage you feel the need to get underneath the car for any reason, then put bricks or blocks under the axle before venturing under the car. Remember, cars are heavy and hard and humans are squishy and fragile.

Now remove the lugnuts competely and put them in a safe place where they won't roll away. The next step is to lift the wheel off the studs. It will feel heavy, so be prepared to have a couple of attempts. Once the wheel is off, roll it to one side and balance it up against something, but put a chock underneath it if there is any risk of it rolling away.

Now, reverse the action to place the spare on the studs. First, make sure the new wheel is the right way around. One side of the wheel is a large hollowed out bowl. This goes next to the car. The other side is more or less flat. This should be facing you as you mount the wheel on the drum. Then make sure the holes on the spare are aligned with the studs on the brake drum. Ready... L-I-F-T!

Once the wheel is hanging on the studs, put one of the lugnuts back on. The tapered part of the nut goes toward the wheel and the flat part goes toward you. Tighten it with a few turns using the wheelbrace. Then place the other nuts on their studs and tighten them by a few turns until all the nuts are in place.

rootbeer277 says The reason the nuts are tapered is to ensure they perfectly center the wheel boltholes on the bolts.

Once all the nuts are in place, use the wheelbrace to tighten them until the wheel is securely on the axle, but don't make them super-tight just yet. If the wheel begins turning, then they are tight enough for this step. Wait until the wheel is on the ground before making them super-tight.

Now go to the jack and drop the car down. It will be easier than raising the car in the first place, but don't get carried away. Do this slowly and gently.

The next step is a safety critical thing. The nuts have to be tight before you drive off. Tighten first one, then one that is almost opposite, then another about a quarter way around and so on, until they are all as tight as you can easily make them. Then go around in the same order, doing them up as tight as you can possibly make them. Use the pipe (but, as rootbeer277 reminds us, be careful about applying too much torque, when tightening), or your weight or any other way to make sure those nuts are tight. You really do not want to have the wheel fall off as you continue up the freeway. Now, replace all the tools and try to get the punctured tyre into the space left by the spare. In older cars it will fit perfectly, but in newer models, the spare tyre is much smaller than the original tyres, so you will need to improvise.

Now, finally, replace all the other junk you had to get out before gaining access to the spare.

Drive off. But go slowly. Those skinny spares are only rated for 80 kph / 50 mph, so do not exceed that. Also, it might be a good idea to visit a garage to make sure those lugnuts are properly tight. And get a new tyre to replace the flat.

It's probably best to have that fitted professionally.

One interesting point to note. 'Spare Tyre' is sometimes used to refer to an extra layer of fat around the midriff. It seems that this extra layer of fat can help to protect vehicle occupants during a crash. People who have the spare tyre, apparently are less likely to die in a road traffic accident.

Reference: http://www.motorinsurance.co.uk/news/1451.html.

So maybe the spare tyre won't disappear after all.

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