A guide to help you know the essentials about tyres
When it comes to vehicle safety, too many drivers neglect their tyres and fail to understand the significant impact cheap tyres (retreads) or worn tyres can have. Balding or worn tyres affect acceleration, braking, directional force and even fuel consumption, not to mention safety since they are the only parts connecting your vehicle to the road. In this guide, we look at tyre markings and how to choose the best tyres for your vehicle and driving needs.
Tyre Markings
When the time comes to replace your tyres, it’s important to understand what type of tyre your car needs. This means getting to grips with the different tyre markings or tyre labels on the sidewall. First, let’s look at the different markings indicating tyre sizing, which has four components followed by the load and speed rating.
- The Nominal section width is indicated by a number such as “195”. This is the widest part of the tyre when fully inflated and is measured in mm.
- The Aspect ratio will also be a number such as “55” which represents the width of the sidewall as a percentage of the nominal section width.
- Radial Construction is indicated by the letter “R”, which refers to the cables radiating around the axis of the tyre.
- The Nominal rim diameter will be measured in inches and indicated by a number, i.e. “16”
Speed Rating Of Vehicle Tyres
The speed rating of a tyre shows what speed that tyre can maintain for 10 minutes without failure. During this test, the speed of the tyre is increased in 10 kph increments every 10 minutes. Since the speed rating should not be lower than the original equipment on the production line of that car, no reputable garage will fit a lower speed rating when you buy a new tyre.
While increasing the speed rating is acceptable on vehicles, speed ratings should be matched on both axles while paying close attention to tyre size. This will help keep your vehicle’s performance characteristics consistent while minimising any associated risks. You should be able to find the speed rating on the tyre sidewall, your vehicle owner’s manual or the sticker inside the driver’s door. Below is a simple table with some of the tyre markings for speed and the typical application for each:
| Load Index | Load in Kg | Load Index | Load in Kg | Load Index | Load in Kg |
|---|---|---|---|---|---|
| 60 | 250 | 74 | 375 | 88 | 560 |
| 61 | 257 | 75 | 387 | 89 | 580 |
| 62 | 265 | 76 | 400 | 90 | 600 |
| 63 | 272 | 77 | 412 | 91 | 615 |
| 64 | 280 | 78 | 425 | 92 | 630 |
| 65 | 290 | 79 | 437 | 93 | 650 |
| 66 | 300 | 80 | 450 | 94 | 670 |
| 67 | 307 | 81 | 462 | 95 | 690 |
| 68 | 315 | 82 | 475 | 96 | 710 |
| 69 | 325 | 83 | 487 | 97 | 730 |
| 70 | 335 | 84 | 500 | 98 | 750 |
| 71 | 345 | 85 | 515 | 99 | 775 |
| 72 | 355 | 86 | 530 | 100 | 800 |
| 73 | 365 | 87 | 545 | 101 | 825 |
Load Index
The load index is a measure of how much weight each tyre can support. A standard car tyre will need a load index that can handle more than 25% of the car’s total weight. This ensures that when the four tyres’ load indexes are combined, they exceed 100% of the mass of the total car, allowing them to safely carry passengers and luggage.
In simple terms, the load index is the maximum weight that a given tyre can carry. For example, a load rating of 80, for example, means that each wheel can support 450kg and when multiplied by four wheels, it adds up to a total vehicle weight limit of 1800kg. Take a look at the load index table below for a better understanding of some tyre sizes and their load indexes.
| Load Index | Load in Kg | Load Index | Load in Kg | Load Index | Load in Kg |
|---|---|---|---|---|---|
| 60 | 250 | 74 | 375 | 88 | 560 |
| 61 | 257 | 75 | 387 | 89 | 580 |
| 62 | 265 | 76 | 400 | 90 | 600 |
| 63 | 272 | 77 | 412 | 91 | 615 |
| 64 | 280 | 78 | 425 | 92 | 630 |
| 65 | 290 | 79 | 437 | 93 | 650 |
| 66 | 300 | 80 | 450 | 94 | 670 |
| 67 | 307 | 81 | 462 | 95 | 690 |
| 68 | 315 | 82 | 475 | 96 | 710 |
| 69 | 325 | 83 | 487 | 97 | 730 |
| 70 | 335 | 84 | 500 | 98 | 750 |
| 71 | 345 | 85 | 515 | 99 | 775 |
| 72 | 355 | 86 | 530 | 100 | 800 |
| 73 | 365 | 87 | 545 | 101 | 825 |
Tyres for commercial vehicles usually have two load index ratings such as “112,110”. The 112 load index correlates to commercial vehicles with a single wheel on each side of an axle holding 1,120kg per tyre. The 110 would be for twinned tyres on each side of an axle, holding 1,060kg per tyre.
What Is The DOT Code On Tyres?
Every tyre has an imprinted DOT code on the sidewall which is short for the Department of Transportation. The DOT code consists of numbers and letters indicating the place and date of the tyre’s manufacture. This is part of the full Tyre Identification Number that helps to better facilitate product recalls. From left to right, the number includes the following:
- The three-character plant code represents the identity of the new tyre manufacturer or retreaded.
- The six-character manufacturer’s code is only used on new tyres and not retreads.
- The date code consisting of four digits indicates the week and the year of manufacture. The first and second digits represent the week while the third and fourth indicate the decade and year respectively.
Fuel Efficiency And Noise Levels
Now that we’ve looked at the tyre size, load index and DOT code, a few other tyre labels or markings are also important, including the following:
- Fuel efficiency is on a sliding scale displayed from A (best) to G (worst). The difference in fuel consumption between a car fitted with A and G class tyres is approximately 0.5 litres per 60 miles (100 km).
- The wet grip performance is measured under controlled conditions and also rated from A (best) to G (worst). The labels include passenger car tyres (C1), light commercial vehicles (C2) and heavy vehicles, trucks, and buses (C3).
- Exterior noise level is measured in decibels (dB) and indicated by using a pictogram showing up to three ‘sound waves’. A single ‘sound wave’ shows a relatively quiet tyre while three ‘sound waves’ indicate a noisier tyre.
What Are Airless Tyres?
Airless tyres are an innovation in automotive engineering that does away with the need for traditional inflated tyres. They use a unique combination of materials and components to create a tyre that provides superior performance, safety and durability, without the need for maintaining air pressure.
In addition to these benefits, airless tyres are also more environmentally friendly by eliminating the need for additional rubber or petroleum-based materials in their construction. They are also much lighter than traditional inflated tyres, which reduces fuel consumption and carbon dioxide emissions from vehicles.
While it may seem like a new concept, Michelin has been working on this technology for over a decade. They showcased their innovation at last year’s Munich auto show by fitting airless tyres to an electric Mini Cooper which had everyone looking on in admiration. If all goes to plan, Michelin believes the technology could be on more cars in the next few years.
Signs You May Need New Tyres
Many customers want to know how long tyres last under normal circumstances but it is often a difficult question to answer. As mentioned in the previous section, tyre longevity depends on various factors including incorrect tyre pressure, improper wheel alignment and driving style.
While tyre age can be determined using the DOT code, it’s important to know the signs that you may need new tyres. Uneven tyre wear is often the first sign that you may need new tyres but you also need to pay attention to the following:
- The vehicle dragging or pulling to one side
- Vibration on the steering wheel
- A sawtooth appearance on the edges of the tyre
- Faster tyre wear on the outer edges than in the middle
- Faster wear of front or rear tyres on front-wheel-drive cars
- Excessive tyre wear on one side
- Cups or dips in the tread
Tyres are not cheap but you can help extend their lifespan by driving properly, performing regular wheel alignment checks and keeping your tyre pressure at the optimum level. Don’t forget to do a physical inspection of your tyres so you can identify any bulges, cracks or worn tread before they become a problem.
For more informative articles on all things motoring, car comparisons, vehicle maintenance, engines, tyres and more, please read our blog.
