Tire size is the most important information given on the tire. The size designation is specified as a series of numbers and letters, for example, 205/55 R 16 94 V XL, where:
- 205 is the width of the tire in mm
- 55 is the aspect ratio (height to width ratio)
- R denotes radial construction
- 16 is the rim diameter in inches
- 94 is the load index
- V is the speed rating
- XL Extra load capacity
The speed rating shows the maximum continuous driving speed capability of the tire. The speed rating to be selected depends on the make and model of car. The use of tires with speed ratings that are too low can affect the driving qualities whereas tires with speed ratings that are too high may reduce driving comfort.
The most important speed ratings are:
- Q = 160 km/h
- S = 180 km/h
- T = 190 km/h
- H = 210 km/h
- V = 240 km/h
- W = 270 km/h
- Y = 300 km/h
What do the first two figures in the marking 205/55 R 16 94 V XL stand for?
They indicate the width of the tire and its profile. In this case, the car accepts a tire that is 205 millimeters wide. The tire profile refers to the ratio between the height and width of the tire. In this case, the height of the tire is 55 per cent of its sectional width.
The registration document also offers a tire with a width and profile of 225/45. Which one should you choose?
In this option, the tire is 20 millimeters wider than in the first example, and it has a substantially lower profile. A wider, lower-profile tire has a better steering feel than a narrower, higher-profile tire. This means that the tire will be more sensitive to the driver's steering movements. A tire like this is suited for a driver who values quick steering response and a sporty feel. On the other hand, a wide tire will be more sensitive to the grooves in the road, and so a driver looking for more comfort may be tempted to select a narrower, higher-profile tire. A narrower tire is also safer on wet roads, as it will displace water better than a wider tire.
What does the letter R that follows the width and tire profile stand for?
It indicates the tire structure. R refers to a radial tire, which is much more stable and precise than its predecessor, the bias-ply tire. What does the letter 16 that follows the letter R stand for?
The number 16 that follows tells us the rim diameter in inches. What should I take into account when choosing rims?
It is important to follow the car manufacturer's instructions. For example, sportier cars will often require rim sizes of 17–19 inches, as smaller sizes will not be able to accommodate the brake systems. Especially when fitting aftermarket rims and tires, you should pay attention to choosing the correct tire width for your rims. Large rims require low-profile tires, whereas smaller rims are suited for higher-profile tires. In other words, if a car requires rims of a size above 16 inches, the driver can no longer choose a higher-profile tire, even if they value driving comfort over a precise driving feel.
What does the last figure in the tire marking stand for?
The last figure is the load index. In our example, the load index is 94, which means that one tire can carry a load of 670 kg. For load index 91, the load per tire is 615 kg. You should choose the correct load index for your car since, otherwise, the tires will wear out quicker than usual and they may become damaged while driving.
What does the letter in the tire marking stand for?
The penultimate letter V gives us the speed rating, or the highest allowed speed for the tire. V means that the tire cannot be driven above 240 kilometers per hour. While it is true that these speeds are illegal in most countries, and certain Countries have directives which state that the tire's speed rating must match the vehicle's top speed. You should also follow the car manufacturer's recommendation when choosing the speed rating because a lower rating may have an adverse effect on the car's handling characteristics, such as steering. A higher speed rating, on the other hand, will reduce driving comfort.
The last letter combination “XL” is not found in all tire markings, why is that?
XL means that the car is suitable for an Extra Load index tire. In our example, the load index is 94. If the index were 91, the XL marking would not be required. Most tire models offer an Extra Load model and a normal load model. An Extra Load model can carry a heavier load, which means that even if you pack more for your summer holiday, you do not need to worry about breaking your tire due to excess load or wearing it out quicker than normal. The sturdier structure of an Extra Load tire means lower heat generation, which makes it more tolerant of wear.
Finally, what does the DOT marking on the tire's sidewall indicate?
This marking makes it easy to check the tire's place of manufacture and age. The two first markings indicate the factory where the tire was made. The four last digits indicate the week and year of manufacture. If the code is 1314, for example, then the tire was manufactured in week 13 of 2014. The recommendation is to use the same tires for a maximum of six years. Even if you do not use your car frequently in the summer, and your tires appear to be in good shape, you should nevertheless replace them at the latest when ten years have passed since their date of manufacture. Over the years, the rubber compound will harden and the tires will lose grip, even if the tires do not wear out otherwise.