In Australia, all tyres must be marked with certain information on the sidewall to comply with Australian Design Rules (ADRs).
Interpret the Number Codes and Markings
Reading a trailer tyre sidewall can provide important information about the tyre’s capabilities and limitations. Here is a guide to help you understand the various codes and numbers found on the sidewall:
1. Width
The width of the tyre is indicated by the first three digits in the tyre size marking. This measurement is given in millimeters and represents the width of the tyre from sidewall to sidewall when mounted on a rim of the specified width. For example, a tyre with the size marking of 205/55R16 has a width of 205mm.
2. Aspect Ratio
The aspect ratio is the ratio of the tyre’s sidewall height to its width. This number is represented by the two digits following the slash in the tyre size marking. For example, a tyre with the size marking of 205/55R16 has an aspect ratio of 55, which means that the sidewall height is 55% of the tyre’s width.
3. Radial Construction
The “R” in the tyre size marking indicates that the tyre has radial construction, which means that the tyre’s plies are arranged radially around the circumference of the tyre. This is the most common type of tyre construction used in modern vehicles.
4. Rim Diameter
The rim diameter is indicated by the last two digits in the tyre size marking. This measurement is given in inches and represents the diameter of the rim that the tyre is designed to fit. For example, a tyre with the size marking of 205/55R16 has a rim diameter of 16 inches.
5. Load Index
The load index is a numerical code that indicates the maximum load capacity of the tyre. This code is usually found immediately following the tyre size marking and is represented by a two- or three-digit number. For example, a tyre with the size marking of 205/55R16 91V has a load index of 91, which corresponds to a maximum load capacity of 615kg. The load rating of tyres is critical for trailers because the tyres are supporting the entire weight of the trailer and its contents. Overloading a tyre can cause it to overheat and potentially fail, leading to loss of control or even a catastrophic accident. It is essential to ensure that the load rating of the tyres matches or exceeds the weight of the trailer and its cargo. This will ensure that the tyres can handle the load and operate safely, reducing the risk of tyre failure and improving overall trailer performance.
Find the right tyre for your vehicle with our comprehensive load index chart:
| Load Index | Maximum Load Capacity (kg) | Load Index | Maximum Load Capacity (kg) | Load Index | Maximum Load Capacity (kg) | Load Index | Maximum Load Capacity (kg) | Load Index | Maximum Load Capacity (kg) |
| 62 | 265 | 75 | 387 | 88 | 560 | 101 | 825 | 114 | 1180 |
| 63 | 272 | 76 | 400 | 89 | 580 | 102 | 850 | 115 | 1215 |
| 64 | 280 | 77 | 412 | 90 | 600 | 103 | 875 | 116 | 1250 |
| 65 | 290 | 78 | 425 | 91 | 615 | 104 | 900 | 117 | 1285 |
| 66 | 300 | 79 | 437 | 92 | 630 | 105 | 925 | 118 | 1320 |
| 67 | 307 | 80 | 450 | 93 | 650 | 106 | 950 | 119 | 1360 |
| 68 | 315 | 81 | 462 | 94 | 670 | 107 | 975 | 120 | 1400 |
| 69 | 325 | 82 | 475 | 95 | 690 | 108 | 1000 | 121 | 1450 |
| 70 | 335 | 83 | 487 | 96 | 710 | 109 | 1030 | 122 | 1500 |
| 71 | 345 | 84 | 500 | 97 | 730 | 110 | 1060 | 123 | 1550 |
| 72 | 355 | 85 | 515 | 98 | 750 | 111 | 1090 | 124 | 1600 |
| 73 | 365 | 86 | 530 | 99 | 775 | 112 | 1120 | 125 | 1650 |
| 74 | 375 | 87 | 545 | 100 | 800 | 113 | 1150 | 126 | 1700 |
6. Speed Rating
The speed rating is a letter code that indicates the maximum speed at which the tyre can safely operate. This code is usually found immediately following the load index and is represented by a single letter. For example, a tyre with the size marking of 205/55R16 91V has a speed rating of V, which corresponds to a maximum speed of 240km/h.
Other Markings
1. 4-Digit Tyre Age
The four-digit code found on a tyre sidewall indicates the week and year of the tyre’s manufacture. The first two digits represent the week, while the second two digits represent the year. For example, a code of 3517 would indicate that the tyre was manufactured in the 35th week of 2017.
2. P, C, LT
P stands for Passenger vehicle tyre.
C stands for Commercial vehicle tyre.
LT stands for Light Truck vehicle tyre (normally used on trailers)
3. M&S
M&S stands for “mud and snow,” and is a designation given to tyres that meet certain performance criteria in snowy or muddy conditions. This marking is typically found on all-season or winter tyres.
4. DOT Codes
The DOT (Department of Transportation) code found on a tyre sidewall is a series of alphanumeric characters that indicates compliance with various safety standards. The code also includes information about the tyre’s manufacturer, the plant where it was produced, and the tyre size and type.
5. E-Marks
E-Marks are a series of alphanumeric characters that indicate compliance with various European safety standards. These markings typically include a capital “E” followed by a number or letter code that corresponds to a specific country or standard.
6. UTQGS
UTQGS (Uniform Tire Quality Grading System) is a standard developed by the U.S. National Highway Traffic Safety Administration that rates tyres based on three criteria: treadwear, traction, and temperature resistance. This information is typically displayed on the tyre sidewall in the form of a code that includes a number for treadwear, a letter for traction, and another letter for temperature resistance.
It’s important to note that there may be additional markings on a tyre sidewall that indicate specific features or properties, such as run-flat capabilities or all-season performance. Always consult the manufacturer’s specifications and seek the advice of a qualified tyre professional to ensure that you select the correct tyre for your vehicle and driving needs.
