Why Pay More? They’re all fat and black BUT Tyres can be different.

December 7, 2006 at 1:17 am Leave a comment

In its simplest form, a tyre is a flexible reinforced bag of air, with two steel hoops built in to hold it on the rim, two woven steel wire belts wrapped around the circumference, and a layer of patterned rubber over that to protect the casing from punctures. If only it was all that simple. Instead, you get layer on layer of complexity, to meet those desirable characteristics that car engineers and drivers demand.

Get this straight though. It’s the air that carries the load. You go no-where without it. More load requires more air, either more volume, or more pressure, or both. More air pressure requires a stronger casing to hold it in. This ‘casing’ is built up of layers of very strong, very flexible tyre cord, which may be polyester, nylon, or in truck tyres, even steel. The bead wire hoops and the layers of rubber, fabric, and other stiffeners transmit the steering and braking forces from the rim to the road surface. If you want the message to get there quicker (faster steering response), you shorten the sidewall, called ‘low profile’ Everything happens where the tyre’s deformable tread surface meets the road, developing friction (grip), so that the car steers, brakes, and accelerates to command. Of course, if the road is slippery like on ice or flooded water on the road surface, then grip suffers.

A tyre needs looking after, but doesn’t always get it. So it has to have reserves of strength, speed capability and endurance built into it, because by the time it’s worn out, it has revolved, and distorted 30 to 40 million times. It also gets overloaded and very hot when run under extreme conditions of load, speed, and temperature. Nonetheless, the modern tyre is very reliable. How big these reserves are affects the cost, so you get what you pay for.

The cheapest tyres then, may have all or some of these characteristics.

A simple tread pattern, which may make it noisy. Simple tyre moulds cost less to make.

A single layer of reinforcing material in the casing, disclosed on many tyres as the number of plies in the sidewall on legend molded onto the tyre

A simple bead/lower sidewall construction, which may affect handling and steering response.

Lower speed capability, as shown by ‘S’ ‘T’ or ’U’ appearing in the size code e g. 195/75R 15 92S

Mid range tyres will have more complex tread patterns, ‘computer scrambled’ to quiet them. These are the type of tyres favoured by car designers of family type sedans.

The belt construction may be more complex, with the larger sizes probably having a layer of nylon over the steel belts, under the tread, to improve durability, and speed capability.

Two ply casing (2 layers of cord in the sidewalls in the legend) to give improved impact resistance.

More complex lower sidewall construction to sharpen steering response (quick lane changing), while still maintaining a comfortable ride at normal tyre pressures.

Improved speed and/or load carrying capacity, or both. e.g. ‘H’, ‘V’ or ‘Z’ appearing in the size code, 92 up to say 96.

Mid-range profiles of 65 to 55, sharpening performance, while still giving a good ride.

Performance tyres align their priorities to maximising grip in wet or dry, and giving top level steering response and speed capability. Some sacrifices in other areas have to be made.

Belt construction may be even more complex. The nylon overlay over the belts may be spirally wrapped, in one thread, so there is no join to open up at very high speed. This takes time, and advanced machinery, and therefore, money.

The lower bead and sidewall construction is more complex. Exotic materials may be used to stiffen the walls for handling, while retaining acceptable ride characteristics at pressures close to normal.

This is where tyre development is concentrated. It has always been easy to over-inflate the tyres to stiffen the sidewalls, at the expense of a bone-shaking ride.

High speed capability is built in, with appropriate pressure increases as specified. Look for Z, W, Y appearing in the size brand.

Maintaining load carrying capacity while lowering the profile, will in many cases, require an increase in rim diameter (e.g. a new set of wheels).

The Australian Design Rule tyre placard fixed to your car, generally on the driver’s side door pillar, dictates the minimum performance levels of your tyres, which must at least match or exceed the load carrying capacity and speed performance of the vehicle.

Your choice of replacement tyres must be guided by these levels.

‘Equal or better, never worse’, is the message.

Entry filed under: Choosing the Right Tyre. Tags: , , .

The number of takeoffs should equal the number of landings Tyre Punctures & Tyre Fires

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