Minecraft Command Science

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Where has the good old-fashioned spare wheel gone? That’s the lament of many a motorist. One of the least-popular trends in modern car design is the almost total disappearance of the traditional full-size spare tyre and spare wheel.

Many drivers, even of today’s modern cars, take one look under the boot carpet of their new vehicle and sigh with disappointment at the sight of a compact space-saver, a canister of green sealant and a compressor to re-inflate a punctured tyre or – on some cars such as BMW or Mini, a run-flat tyre, which is designed to be able to be driven with no air pressure for a short while.

Why have spare tyres / spare wheels disappeared? There are several reasons why modern cars no longer come with a full-size spare wheel. The main one is fairly simple: they are rarely used. Most spares spend their entire life hidden in the boot, so there are considerable savings to be made by not fitting them.

The main three savings are cost, space and weight. A typical 17″ alloy wheel and tyre would cost the manufacturer about £100 and weigh about 20kg. A full-size wheel is also bulky, so designers have to factor in enough space for the wheel to fit in or under the boot – and that adds more bulk and weight to the vehicle.

By replacing the full-size wheel with a space-saver spare wheel, costs go down and weight is saved. If you have a ‘breakdown kit’ of goo and compressor, the weight, space and cost savings are even greater.

The saved weight makes a small difference to fuel economy and emissions, which can help lower a car’s CO2 rating (and potentially reduce road tax). Smaller cars like hatchbacks and sports cars gain the most from the saved space, but the cost savings are universal.

So what are the pros and cons of each tyre emergency alternative?

Full-size spare wheel Full-size spare wheel, spare tyre The default spare wheel offering until the 1990s and now virtually non-existent. Until recent years, it was considered standard practice for all cars to come with five identical wheels and tyres – four on the road and one in the boot.

This option means that any tyre can be immediately replaced with the spare on the spot, and there are no limitations to speed and distance when the spare wheel is in place.

These factors are still crucial in more remote parts of the world, where it’s easy to be a long way from your local tyre shop. There is also the caveat that the spare is only useful if it is in good working order and not flat! This sounds obvious, but the number of people who never check their spare tyre – or who use it to replace a flat tyre and never get the damaged one fixed – is staggering. So it’s useless when you actually need it.

Also, most drivers don’t bother replacigg the spare tyre when replacing the other four tyres, so it is often a different tyre to the other four anyway, which is not ideal from a safety perspective.

Pros: convenient, as long as all four wheels are the same size; no speed or distance limitations when running spare wheel Cons: expensive, heavy and bulky for something which is rarely used; few people ever check the tyre pressure on the spare, so it could be be flat when you actually need it.

Space-saver spare wheel Space-saver spare wheel, spare tyre Compact space-saver spare wheels emerged in the 1980s as manufacturers looked to start saving money and weight in their cars.

It was also becoming more common for cars to come with different-sized front and rear tyres and/or directional tyres, meaning that it was possible that a car could have four different tyres on four wheels! This meant that one full-size spare wheel had a 75% chance of being the wrong wheel for the job.

One common problem with a space-saver spare wheel is that if you ever need to use it, the original full-size wheel and flat tyre won’t fit in the spare wheel well, so you have to carry it in the boot – which, of course, is no good if you already have a bootful of luggage or a very small boot.

Space-saver spare tyres are also usually limited to a maximum speed of 50mph (80 km/h) and a maximum distance of about 50 miles, so it limits your options for getting to a suitable tyre shop. Your steering and braking performance will also be affected, so it’s very much a temporary solution.

Pros: cheaper, lighter and smaller than a full-size spare tyre; can be used for almost any tyre problem Cons: your damaged full-size tyre won’t fit in the space-saver wheel well; limited speed and distance; vehicle handling and safety impaired

Breakdown kits Tyre sealant breakdown kit (c) Continental Corporation Breakdown kits, also known as tyre inflation kits, consist of a bottle of sealant liquid and an air compressor. They’ve become a lot more popular in recent years, and are now becoming the default solution for most new cars. However, they are far from perfect. The theory is that you squirt the green goo into the tyre valve and then use the compressor to reinflate the flat tyre.

Again, this is a temporary fix and usually limited to about 50 miles at no more than 50mph. Whilst it does mean that you don’t have to worry about changing the tyre and emptying your boot, it is only really useful for relatively minor punctures and no good whatsoever if the tyre has suffered significant damage.

Pros: re-inflating tyre means no need to change a wheel on the roadside; maximum cost/space/weight savings (no spare wheel, wheel well, jack, tyre lever, etc.) Cons: only suitable for minor tyre damage; limited speed and distance; using sealant usually makes tyre irreparable

Run-flat tyres Run-flat tyre Run-flat tyres have long been championed by BMW, and are slowly being adopted by some other brands as they improve in terms of cost and ride comfort.

These tyres feature a reinforced sidewall that allows you to continue driving on a punctured tyre even if it has lost all of its air (again, you’re limited in speed and distance).

The downsides to run-flat tyres are that they are again limited to minor punctures rather than serious cuts, and the reinforced sidewalls are much more rigid than those of a normal tyre, which usually makes your ride a lot bumpier than on a regular tyre.

Pros: maximum convenience, with no need to stop to change or repair the tyre; maximum cost/space/weight savings Cons: only suitable for minor tyre damage; limited speed and damage; tyres are expensive; significantly reduced ride comfort.

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