Buying tires may not be the most glamorous purchase you can ever make, but it is certainly one of the most important, since your life depends on the choices you make. If you do a lot of high-speed driving on highways, you definitely want tires that will not only last long, but also provide the best braking, steering, and handling characteristics in all types of weather conditions. However, if you only do a few miles of city driving each day, do you really need premium, branded tires?
Where do you begin to choose the tires that are best for you? With so many brands, types, sizes, and other design features, how do you know which is best for your particular conditions or needs? Read on, and we will tell how to go about choosing the right tires for you.
First Things First
The first thing to remember is that the final design of a tire depends on many factors, and since not all of the best of each factor can be incorporated, the final product is the result of a lot of trade-offs between the various requirements that make a tyre last for a reasonable amount of time, while still providing adequate traction at the least amount of noise.
Some of the considerations that go into the design of a tire include the following, and the final product is a series of compromises between all of these factors:
- Traction on dry surfaces
- Traction on wet surfaces
- Traction during dry cornering
- Traction during wet cornering
- Amount of rolling resistance
- Road noise
- Steering characteristics
- Resistance against perforation
- Provide good quality
- Be able to cope with high speeds
- Be able to cope with heavy loads
- Provide off-road traction
In practice, all of this means that while it is possible to make a tire with exceptional traction, it may last for only about 10 000 kms or so, but if a harder compound is used, the tire may well last for 80 000 km, but with a corresponding reduction in traction, and braking/steering performance.
To overcome the durability/traction problem, many tire manufacturers now include varying amounts of silica in rubber compounds, which improves traction, without seriously affecting durability. However, there are other issues to consider when you are shopping for tires besides traction and durability, so let us look at some things to look out for on good quality tires.
Tyre noise is the result of the way the tread blocks vibrate when the contact the road surface, which is why tire manufacturers use different sized tread, blocks. The differences are not huge, but the fact that the tread blocks are of different sizes means that to a large degree the vibrations of one size of tread block cancels out, or masks the vibrations of other tread blocks, which results in substantially reduced road noise.
Asymmetric Tread Patterns
On tires of this type, the tread blocks on the outside edge of the tire are bigger than the tread blocks in the center of the tread. This results in better grip while cornering, but the since the tread blocks are smaller, and spaced more closely together in the center of the tread, more rubber is brought into contact with the road, which translated into better straight line tracking. In addition, asymmetric tires have specially designed tread patterns on their inside edges, which increases the tire’s ability to drain water from the treads.
All of these factors increases a tire’s traction in both wet and dry conditions, and that can be used on all four wheels, but they have to be mounted in a specific way, with the clearly marked “Outside” marking on the outside of the tire in all cases. However, these tires can only be rotated between the front and rear axles, since they are also directional, with an arrow on the sidewall that indicates the direction of the car’s motion. Swapping theses tire from side to side means that the tires will rotate in the wrong direction, which means they will NOT perform to specification, which is dangerous, since the tires will overheat, and possibly disintegrate as a result.
While asymmetrical tires offer excellent grip and handling characteristics, they never last as long as tires with symmetrical tread patterns.
Retreads vs. New Tires
Rereading a tire means placing a band of tread on an old tire casing, which raises all sort of questions about safety and reliability, since the tread in not an integral part of the tire, as it is in the case of a new tire.
Of primary concern is the fact that the history of the casing is not known; it may have subjected by abuse, or impacts that could have damaged or destroyed the reinforcing steel bands, or it may have been driven in a deflated condition, which could have caused serious damage to the side walls. For these reasons the manufacture, distribution, sale, and use of retreaded tires is banned outright in many countries.
However, in recent years, the markets in many countries have been flooded by cheap, dangerous retreads from China, and while they may appear to a bargain, these tires are dangerous, and must be avoided at all costs. Even with the cheapest new tires, you will be better off than you would even be with even the “best” retreads.
What Do The Numbers Mean?
The combination of letters and numbers on the sidewall of a tire describe all of the features of that tire, and while it may look like gibberish to the uninitiated, the numbers are not so difficult to decipher as you might think. Let us take as an example the numbers and letter on a tire that is in common use the world over:
Bridgestone Potenza 225/45 R17 91Z
Let us look at each element of the above example in turn:
- “Bridgestone” refers to the brand name.
- “Potenza” refers to the range, or model within the brand name.
- On some tires, the next element would be either a “P”, “LT”, “M”, or “T”, and although these letters do not appear in our example, they mean the following:
• “P” would refer to the fact that the tire is designed for use on passenger cars and some 4WD vehicles.
• “LT” means the tire is designed for use on light trucks.
• “M” means the tire is meant for use on motor cycles.
• “T” means the tire is for temporary or emergency use only, such as a “space saver” spare wheel.
- “225” refers to the width of the tread, which in this case, is 225 millimeters.
- The “45” after the slash refers to the height, or profile of the tire, as measured from the bead to the tread surface. However, this measurement is always expressed as a percentage of the tread width, and not as an actual measurement in mm. In this case, the percentage is 45, which translates into 45% of the tread width, which works out to 101.25 mm. The lower the profile, the better the tire performs, but this comes with a serious reduction in ride comfort.
- The “R” in the sequence refers to the construction of the tire, which in this case is of the radial type. This means that the tire is reinforced by bands of steel that are arranged radially around the circumference of the tire, as opposed to across the width of the tire as in the case of cross-ply tires. Radial tires are by far the most common, since the arrangement of the reinforcing bands help to maintain the shape of the tire, especially at high speed.
- “17” refers to the diameter of the tire, as measured in inches between the bead surfaces along the middle of the tire. As a rule of thumb, tires get more expensive the larger diameters they have, but paradoxically, smaller tires such as 12-, and 13 inch tires can be more expensive than 16-, and even 17 inch tires in some markets because fewer cars that use them are being made.
- “91” refers to the maximum load a tire can be subjected to if it is inflated correctly. On some tires, this value will be expressed in kilograms or pounds, but it is much more likely to be expressed as an index number, which in this case refers to a maximum weight of between 600-, and 630 kilograms, per tire, but this does NOT mean that this figure can be multiplied by four- this weight refers to the maximum weight each tire can bear, and it must NEVER be exceeded. The table below lists the accepted load rating index numbers, and the corresponding weights in kilograms.
|Load rating number||Maximum load per tyre (kg)|
- The last element, “Z”, refers to the maximum speed the tire is designed to cope with, which in this case, is in excess of 240 km/h. The table below lists speed index numbers, and the corresponding speeds in km/h.
Load rating number Maximum load per tire (kg)
I almost all jurisdictions in the world, you are obliged by law to use tires on which the speed rating is suitable for your car, and the rating has to be the same, or higher than the rating on the tires your car left the factory with. However, while there is no known minimum speed rating, the highest rating, which is “Z”, and applies to speeds over 240 km/h, means that the tire is guaranteed to last for only ten minutes at that speed before you run the risk of the tire disintegrating.
The two single most important factors that determine how long your tires last, are proper inflation, and wheel alignment.
Even if your car is equipped with a tire pressure monitoring system, never rely on it to always be accurate. Purchase a good quality digital tire pressure gauge can be had for about the same price as cup of take-out coffee, so get one, keep it in the glove box, and check your tire pressures at least once a week when the tires are cold.
You may be surprised at how long your tires last compared to the previous set when once you get into the habit of maintaining correct tire pressures and proper wheel alignment!