Sidewall of a new tire contains a lot of symbols that are called marking. The majority of symbols are technical but there are some that can be useful for a purchaser.
When choosing new tires one is guided by their size. Size includes three basic parameters: width, height, tire design and wheel diameter as well as speed symbols and load indices.
For example: 185/65 R15 92 T
• 185 – width of tire profile (also known as “section width”) in millimeters;
• 65 – tire profile height that is indicated as percentage ratio to the width (also known as “aspect ratio”). Very often it is called a series. In some sizes series number is absent, for example, 185 R14 C 102 Q. Such tires are called full-profile and the ratio of height to width in this case amounts to 80% or 82%.
• R – a symbol that describes tire design (R – radial);
• 15 – wheel diameter (diameter of a wheel on which the tire is to be mounted);
• 92 – load index that shows acceptable load in kilograms. In most cases You can find Max Load sign that is followed by two figures – the first in kilos, the second in pounds.
• T – speed symbol. It points at the maximal acceptable speed at which the manufacturer guarantees maintenance of the designed driving properties of the tire.
Some sizes have additional letter symbols: 185 R14C 102 Q, C symbol is used for so-called “Commercial” tires with big load index that are intended for light trucks.
American tire marking (P-metric)
American tire manufacturers use their own marking. There are two marking types:
The first looks like European. The only difference is “P” letter (Passenger – for passenger cars) or “LT” letter (Light Truck) that is put before the marking. For example: P195/55R14 or LT235/65R15.
The other marking differs from the first one greatly.
For example: 31x10.5R15
• 31 – outer tire diameter in inches;
• 10.5 – tire width in inches;
• R – radial tire;
• 15 – inner tire diameter in inches.
1. Tread wear indicators
2. Model name
3. Additional data on carcass and breaker construction peculiarities
4. Maximal load and pressure requirements
5. Mark that shows external tire side (needed for correct alignment)
6. Tire construction mark (R – radial)
7. Tire width in mm
8. Aspect ratio (ratio of tire height to tire width)
9. Tire construction mark (R – radial)
10. Wheel diameter in inches
11. Load index
12. Speed symbol
13. Mark that allows to define whether the tire has a tube (Tubeless – if the tire doesn’t have a tube, if the mark is absent – tire has a tube)
14. Symbol and number of ECE-type conformity
15. DOT mark means that the tire is approved by the US ministry of transport
16. UTQG mark (Uniform Tire Quality Grade) is used for tires sold in the United States and is placed on the sidewall as a seal. UTQG shows three parameters obtained in the course of the tire testing: Treadwear – relative expected mileage; Traction – tire’s braking performance on wet road surface; Temperature – tire’s thermal resistance at high speeds on the test desk
17. Manufacturing country
18. Brand’s name
When buying a tire it is extremely important to check its manufacturing date as tires are exposed to aging and in the course of time lose their performance even if they are not operated. In most countries warranty period covers 5 years.
Modern tires have manufacturing date stamped as a four-digit number after the DOT standard code. The index comprises four digits. The digits mark the week and the year of manufacture. If the index has only three digits the tire was manufactured in the 80ies, if there is a triangle after the digits the tire was manufactured in the 90ies. In our case (see the photo) there is a 3103 four-digit mark which means that tire was manufactured in 2003, week 31.
It is worth noting that the majority of manufacturers produce winter tires in the first half-year. It allows to store up products to provide the wholesalers with tires promptly in the fall of the year.
If You want to change wheels on Your car You need to know a few important things for the right choice. All wheels have standard marking regardless of their type (steel or alloy).
For example: 8.5Jx18 H2 5x120 ET20 d74.1
• 8.5 – wheel width in inches (W)
• 18 – wheels diameter in inches (D)
• 5x120 – shows the number of wheel bolts and diameter at which they are placed. The diameter can also be marked as PCD and measured in millimeters. In our case there are 5 wheel bolts and PCD is 20mm.
• d74.1 – diameter of the central bolt hole that is measured from the mating face side. The diameter (DIA) is measured in millimeters. In our case it is 74.1mm. Many manufacturers of alloy wheels make bigger diameter of DIA and use centering rings for hub alignment. The rings fix the wheel securely thus eliminating vibrations.
The marking also contains additional J and H2 parameters but they are interesting only to specialists.
• J – marks information on the construction of rim edges. There are following types: J, JJ, K, JK, B, P and D.
• H2 – marks hump construction. The types are H, H2, FH, FH2, CH, EH2, EH2+.
Let’s consider each of parameters in detail.
We think that the wheel width and diameter do not need additional explanation.
As it has been mentioned above, PCD is a diameter of circle on which bolt holes are placed (marked with a red line on the picture below).
If necessary one can calculate PCD by measuring the distance between the centers of near holes (it can be done by a regular ruler without removing the wheel from the car). On four-wheel bolts PCD equals the distance between the centers of the opposite bolts.
Following formulae are applied for PCD calculating:
• 3 holes: PCD=X*1.154
• 4 holes: PCD=X*1.414
• 5 holes: PCD=X*1.701
• 6 holes: PCD=X*2
• 10 holes:PCD=X*3.326
ATTENTION!
As bolt holes are made with considerable size tolerance one can easily mistaken when choosing PCD even if it differs from the right one by a few millimeters.
For example, PCD 98x4 wheels are often mounted on PCD 100x4 hub (one cannot distinguish between 98mm and 100m). IT IS UNACCEPTABLE! In this case only one of the bolts will be tightened properly. The fixing of the other bolts will be loose what can lead to their untwisting when riding.
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