Tyre Size Guide

Tyre Size Guide

Most car owners pay more attention to the engine because they believe it has the biggest influence on how their driving experience will be like. However, it is also just as useful to look at the car Tyres and its influence on how smooth and safe your ride will be. After all, the Tyres are the ones that actually touch the road you are driving on. Thus, understanding how to choose the best ones for your car can greatly improve your driving. Beyond identifying the type of Tyre and Tyre tread you need, you also need to know the right size. There are a few measurements necessary to know whether the Tyre fits your car model, and here is a short guide to converting what these numbers mean. The most important of these are the width and diameter, but other factors like speed rating will also be explained.  The key is to look at the combination of letters and numbers on the Tyre itself. They stand for various measurements and other identifying markers that help you decide if you have the right Tyre.

  • Tyre Type

The first identifier is one/two letters. Cars in the United States state P, meaning it is a P-Metric Tyre manufactured for passenger vehicles. This also means they uphold certain standards in the US. On the other hand, if there is no letter, then it means it is a Euro-Metric Tyre, which has different load capacities. There are also Tyres marked LT, which means the Tyre was manufactured for light trucks. These Tyres need higher pressure than passenger Tyres because of the load.

  • Tyre Width

This refers to the measurement of the Tyre’s width in millimetres, from one sidewall to another. These stand for the first 3 digits, which means in a Tyre marked P215/65 R15 91S, it has a width of 215 millimetres.

  • Aspect Ratio

The next two numbers after the slash mark refer to the aspect ratio or the ratio of the Tyre cross-section’s height to the width. In the example above, this means the Tyre’s height is about 65% of the width. When the aspect ratio is bigger, then the sidewall is also bigger.

  • Construction

The next letter stands for the construction of the Tyre, where the R in the example stands for Radial.

  • Wheel Diameter

This number stands for the wheel size measured from one side to another. It also determines which kind of wheel the Tyre is meant to fit. In the example, this means the Tyre is manufactured for a wheel that has a 15-inch diameter.

  • Load Index

The next two numbers refer to the load index, of the maximum load that the Tyre is able to support when it is inflated properly. The same information is also found on the sidewall, both in pounds and kilos.

  • Speed Rating

The last letter stands for the maximum speed capability of the Tyre. Each letter stands for a certain driving speed, which manufacturers recommend that owners do not exceed. This alphanumeric combination can be found on the Tyre itself, as well as the door jamb on the driver’s side, inside the door of the glove box, and within the hatch of the gas tank. You may also read about it in the manual of your vehicle.

There is a large variety of car Tyres out there in the market. It is not, however, as simple as just mounting any Tyre on your car, because there are several factors you need to consider, like how you generally use your car and the condition of the road you will be normally driving on. Relaxed drivers would not require the same kind of Tyre as someone who loves to speed down the road like an F1 racer. For example, one with treads will only slow you down because of the small contact patch on the tarmac. The purpose of your car (and Tyres) will dictate what Tyre you should buy. A second factor is the driving condition when you are on the road. Snowy conditions bring a lot of danger of slipping around the street, so you need Tyres that have big tread blocks, deep grooves with minute metal studs embedded in the tread that grip the ice and snow.  Third, driving comfort can be greatly influenced by your choice of Tyres. The tread patterns generate noise, which is why you should choose the right Tyre to minimize these vibrations.

  • Summer or Performance Tyres

This type is perfect for speeding down the highway, as it is manufactured from soft rubber compounds and very little tread pattern to even none. This means you can go fast but at the same time, have the necessary grip to prevent you from sliding off the pavement. When you have performance Tyres, though, you cannot expect a lot of mileage. Its top qualities are grip and performance.

  • All-Season or All-Around Tyres

Cars that come out of the assembly line and most likely what you end up buying comes with all-around or all-season Tyres. They have the right combination of grip, performance, safety in wet weather conditions, durability, and acceptable noise. These Tyres are made of rubber compounds that are harder than the summer Tyres, which means it has worse performance and grip. However, this is not necessary for the day-to-day driver, which is why 9 out of 10 motorists use this type of Tyres all the time. Moreover, it has the right balance between a silent drive and still performing very well when there are heavy downpour and wet road conditions. If you do not have particularly special requirements, this kind of Tyre is perfect for you.

  • Wet Weather Tyres

Wet weather Tyres are not that different from summer Tyres, in the sense that they are also made of softer rubber compounds as opposed to all-season ones. The major difference between wet weather Tyres and summer ones is that they have more siping that work on channelling the water away from the contact patch of the Tyre. During the rainy season, Tyres should quickly heat up in order to ensure the contact with the road’s surface. This is the reason why it comes with a contact patch wider than an all-season Tyre.

  • Winter Tyres

Difficult is an understatement when describing driving in snowy conditions. In fact, having the wrong Tyres can definitely cause an accident. This is the reason why there are winter Tyres, exactly for the purpose of allowing you to drive safely in slippery, icy roads. There are two kinds of winter Tyre compounds, suitable for different conditions. If you are driving in snowy and muddy conditions, then M&S Tyres are the ones you should install in your car. However, snowy and icy roads require bigger block patterns that offer the best contact with the road’s surface. These are the ones with the snowflake symbol, and many of them have embedded metal studs to give the Tyres a better grip when the roads are covered in snow. Unfortunately, this kind of Tyres has a noisy downside.

  • All-Terrain Tyres

Light trucks and SUVs would find this kind of Tyres most suitable. They have sidewalls that are quite stiff, which allow these vehicles to carry heavy loads and go over rocks and whatever obstacles lie in rough roads. They also come equipped with bigger tread block patterns, which means they have enough grip while driving on gravel, dirt, and loose sand. The disadvantage is that these large tread blocks make the rollers noisier than other Tyres. They also have less contact surface on roads that are paved. This means you will not be able to speed up on highways without taking the risk of slipping or even turning over. These Tyres are neither hard nor soft, they are just right in the middle.

  • Mud Tyres

These Tyres are similar to all-terrain Tyres, in the sense that their compound’s tread block patterns are huge and even chunky. These Tyres are not at all suitable for driving on other surfaces unless it is muddy and dirty. In some cases, these tread blocks do not resemble blocks at all and instead, look like chunky paddles.

The Different Tread Patterns

The tread pattern is a huge factor in choosing the right Tyre for your vehicle. The tread pattern can have a great impact on traction, as well as in durability and handling. If you also want a smooth, noise-free, and comfortable ride that may also impact your car’s fuel efficiency, then you need to understand more about the three available Tyre tread patterns to choose from.

1. Symmetrical

This type of pattern normally has a uniform design. This means if you make a lengthwise cut of the Tyre along the grain to have two complete Tyres, both the right and the left would have an identical tread design. This is the reason why it is named symmetrical tread pattern.

2. Asymmetrical

Now if you slice a Tyre with an asymmetrical pattern, then you would not come up with similar designs. Moreover, this type of Tyre pattern tends to have bigger tread blocks on the outer part of the compound. This is so that the Tyres stay stable while cornering. On the other hand, the inner Tyre section has blocks that are smaller and they also have water-channelling grooves, which function as heat dispersion from the rubber compound.

3. Unidirectional

For cars that need acceleration in a straight direction, this type of tread pattern is best. They look like symmetrical tread patterns in the way that the Tyre halves look identical. However, it has a feature that makes it stand out. These Tyres are specially designed to turn only in one direction. This means you need to look for an arrow on the side of the Tyre to see the correct direction when mounting them on your vehicle. This is very important because if you install them in the wrong direction, you will face very serious problems. In short, this tread pattern allows you to accelerate better due to less rolling resistance. Some may also require a shorter distance when stopping, making it ideal for performance cars that need quick acceleration and short stopping distance.

Can You Install A Different Tyre Size On Your Car?

Your car manufacturer states exactly what Tyre size is suited for your vehicle. These markings make it easy for consumers like you to find the right one and prevent making a wrong purchase. Some people are, however, interested in converting to a different size. This is not specifically what your car maker suggests, but if you follow very stringent criteria, it may be possible. Without following these, you will suffer the consequences like voiding the warranty and other risks. The key is to stick as close to your original Tyre’s diameter as possible. This is the most important thing, because various factors, like the gear settings, brakes, torque, speedometer, and tractor control are based on the diameter, which dictates how far the Tyre must travel to get a full rotation. If the time or the length it takes for a full revolution is affected, your speedometer might show inaccurate readings, and your gears will also be affected.

This is the reason why the overall diameter should always be as close to the Tyre that your car was designed to run with. Unfortunately, it is not as easy to compute the outside diameter because Tyre sizes only include the inside diameter measurements. There are, however, online Tyre size calculators that help you compute whether the Tyres have similar overall diameters. The rule is, if you want to change your Tyre size, they should not have a difference in diameter of more than 1%, ideally, it should be less than that. Another tip is to consult an expert when considering a Tyre with a different size. They will be better at advising you if you are increasing your risk of getting an accident or damaging your car. Otherwise, it’s always a good idea to just stick to your vehicle’s original Tyre size to avoid any unwanted consequences that might affect your car’s performance.

Taking Care Of Your Tyres

Because your Tyres can determine your car’s performance and your driving experience, it is important to always get the right Tyres and to take necessary steps to maintain it. Here are some tips you can follow:

  • Regular Inspection

Even if you are not an expert, you can still check your tyres every once in a while. You can do a visual inspection of any damage or wear and tear, especially if you regularly look at your Tyres. If you see something amiss, then you can bring your vehicle to an expert to have it looked at.  Better still, you can have a professional inspect your tyres at least once a year.

  • Keep The Right Air Pressure

Another habit you should develop is to check your Tyre’s air pressure regularly. If you drive with not enough pressure, the vehicle’s performance might be affected, especially when the weather is rainy or icy. Moreover, cold weather will also cause the Tyre pressure to quickly fluctuate. A good trick is to do a monthly check of your Tyre’s pressure, and adding just a bit more air in.

  • Keep The Load Index In Mind

The Tyres have a maximum weight they can withstand. Going over will result to overheating and eventually lead to its destruction. If you are not aware of the load index, you can check the manual and the numbers listed on the sidewall.

  • Avoid Speeding

As mentioned above, not only is the weight limit stated on the Tyre but also the speed limit you are restricted to. Driving too fast or over this limit, will ultimately shorten its lifespan not to mention compromising your safety.

  • Rotate Your Tyres

Another important step to prevent wear and tear is to rotate them. This way, they will not wear down unevenly. This is a step that can be done once or twice a year, pairing it with other regular maintenance steps like an oil change.

  • Use The Spare Tyre

If your Tyre is damaged in any way, do not take the risk in driving with it. Instead, use your spare Tyre until it was inspected by a professional.


    We are committed to offering customers our most competitive and irresistible tyre prices in Australia.

    Learn more

    Tyrepoint has over 100 approved fitment centres across Australia, all of which have state-of-the-art equipment.

    Learn more

    For your convenience, we have answered a series of FAQs about our services.

    Learn more

    Contact Number: 1300 089 733

    Our customer service opening hours are

    Monday to Friday       8:00am to 5:30pm
    Saturday      8:00am to 3:30pm