Published on Jan 19, 2016
Air-filled tires are known as pneumatic tires, and these are the type in almost universal use today. Pneumatic tires are made of a flexible elastomer material such as rubber with reinforcing threads/wires inside the elastomer material. The air compresses as the wheel goes over a bump and acts as a shock absorber.
Tires are inflated through a valve, typically a Schrader valve on automobiles and most bicycle tires, or a Presta valve on high performance bicycles. Attempts have been made to make various types of solid tire but none has so far met with much success. The air in conventional pneumatic tires acts as a near constant rate spring because the decrease in the tire's volume as the tire compresses over a bump is minimal. "Airless" tires usually employ a type of foam or sponge like construction which consists of a large number of small air filled cells.
As a result, compression is localised within the tire and the effective spring rate rises sharply as the tire compresses. The result is a tire which is less forgiving, particularly with regards to sharp transient bumps and provides poor ride and handling characteristics. The "steering feel" of such tires is also different from that of pneumatic tires, as their solidity does not allow the amount of torsion that exists in the carcass of a pneumatic tire under steering forces, and the resultant sensory feedback through the steering apparatus; as a result they feel as if they are pivoting on bearings at the contact point. They are more popular for bicycles than for automobiles, which have tires which are much more robust and immune to puncture.
The outer perimeter of the tire, often called the crown, has various designs of jagged shaped grooves in it, known as the tread. These grooves are especially useful during rain or snow. The water from the rain is compressed into the grooves by the vehicle's weight, providing better traction at the tire-to-road contact. The sidewalls are the sections of the tire which are between the crown and the inner circular edges of the tire contacting the rim. To avoid tearing at these inner edges, particularly when the tire is being mounted, there are a number of concentric steel wires buried inside the rubber at both inner edges of the tire. This inner rim is called the bead.
Some air-filled tires, especially those used with spoked wheels such as on bicycles and motorcycles, or on vehicles travelling on rough roads, have an inner tube; this was also formerly the case of automobile tires. This is a fully sealed rubber tube with a valve to control flow of air in and out. Others, including modern radial tires, use a seal between the metal wheel and the tire to maintain the internal air pressure (tubeless tire). This method, however, tends to fail if the vehicle is used on rough roads as a small bend on the rim (metal wheel) will result in deflation. The inner tubes are usually made of halobutyl rubber, because of its suitable mechanical properties and excellent impermeability for air.
Pneumatic tires generally have reinforcing threads in them; based on the orientation of the threads, they are classified as bias-ply/cross ply or radial. Tires with radial yarns (known as radial tires) are standard for almost all modern automobiles, whereas bias-ply tires are the norm for trailers.
Semi-pneumatic tires have a hollow center, but they are not pressurized. They are light-weight, low-cost, puncture proof, and provide cushioning. These tires often come as a complete assembly with the wheel and even integral ball bearings They are used on , wheelbarrows. They can also be rugged, typically used in industrial applications, and are designed to not pull off their rim under use.
Tires that are hollow but are not pressurized have also been designed for automotive use, such as the tweel(a portmanteau of tire and wheel), which is an experimental tire design being developed at Michelin. The outer casing is rubber as in ordinary radial tires, but the interior has special compressible polyurethane springs to contribute to a comfortable ride. Besides the impossibility of going flat, the tires are intended to combine the comfort offered by higher-profile tires (with tall sidewalls) with the resistance to cornering forces offered by low profile tires. They have not yet been delivered for broad market
TYPES OF TYRES
1) Standard/ All Season Tyre
Your car was probably driven out of the factory on all season tyres. It is an average tyre that is suitable for all year round use. It works equally well in the wet and the dry.
The tread block pattern is designed not to be noisy when used on standard roads but enables adequate water dispersion to provide grip in wet conditions.
The rubber used is a harder compound to extend the tyre's life. This can comprise on handling and cornering but for the majority of drivers it is not noticeable.
2) Performance Tyre
Also known as summer tyres, performance tyres are designed for provide excellent grip in the dry. Often used on fast cars or for a driver whose style requires increased handling performance. They can be used all year round if you live in a region with a warm climate and little rain.
A soft rubber compound is used which decreases the lifespan of the tyre but provides enhanced grip.
It is important that the car tyres are kept in excellent condition. Driving in the wet is hard enough with these tyres but if there is any sign of wear it is virtually impossible to get good grip.
3) Winter Tyre
Winter car tyres are designed to cope with the poor weather and difficult driving conditions that the winter season brings. They can handle snow and ice. Winter tyres can have small metal studs embedded into the tread for extra grip in extreme conditions.
The tread block pattern on winter car tyres is larger and more pronounced than on standard tyres. This improves grip but also increases the tyres' operating noise.
These tyres cannot be used all year round because in dry conditions they wear out extremely quickly and damage the road surface.
4) All Terrain Tyre
All terrain tyres provide good grip on loose surfaces such as dirt and sand. Often used by off road vehicles, they can be used on standard roads but are very noisy.
Like the winter tyre the tread block pattern is large to improve grip. The tyre's sidewalls are stiffer to cope with uneven surfaces and unexpected potholes.
Mud tyres are an extreme type of all terrain tyres, designed to be used in mud and dirt. They have very large tread block patterns that are only suitable for driving on that type of terrain.
5) Run Flat Tyres
Run flat tyres are a relatively new concept but are now becoming more common on new cars. They are designed to minimise the loss of handling that occurs after a puncture.
The car tyre can operate without air to enable the vehicle to continue to be driven. However this is only suitable for a short distance and at a reduced speed, until the tyre can be safely changed.
For further advice consult a car tyre specialist who will provide you with impartial advice on the best tyres for your vehicle.
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