What Do The Numbers On Tyres Mean?

A Closer Look At Car Tyres

If you've ever inspected your car tyres, then you have definitely seen some letters and numbers on their sides. You may have wondered what purpose the bunch of random letters and numbers serve. Read on to understand what the letters and numbers on car tyres mean.

Each car has tyres made to carry a certain amount of load when moving at a specific maximum speed. On each car tyre's side, you will find the brand name and the model written in the biggest letters. In addition, there are other smaller numbers and letters whose meanings are essential to understand as a car owner.

This is the case because they help you know your car tyres more. They are also crucial in selecting the proper tyres for your car when you need to replace them. Let's dive deeper to better understand what these numbers mean.

Tyre Numbers And Their Meaning

Section width

Let's start with the number 245 on your car tyre, which represents the section width. The section width is usually measured on the most probable width of a wheel designed to function for your car model. The measurement distance is measured in millimetres and is generally taken from the maximum width of a given tyre's mid-point of the sidewall to the exact point of the opposite sidewall. Simply put, the number 245 is the measurement from each tyre's inner sidewall to the outer sidewall.

The aspect ratio or tyre profile

The number 40 on your car tyres represents the aspect ratio or profile. Each tyre's sidewall height is expressed as a percentage of your section width. For the example provided above, the tyre's sidewall height is 40 per cent of the tyre section width of 245. The bigger the tyre profile or aspect ratio, the bigger the sidewall.

The construction code R shows that your car tyre is manufactured using a radial ply construction. Most cars feature a radial construction, a design in which the cord plies are placed radially or at a 90-degree angle to the direction of travel. However, if you have an old trailer tyre, you may find the tyre size indicated as B78-13.

The dash shows that the tyre is of bias construction instead of radial. A bias ply tyre's sidewall is a symmetrical design with an even number of crossing plies. The B78 shows that it uses some traditional sizing form.

Tyre rim

The diameter of your tyre rim is usually measured in inches. The measurement usually shows the size of your rim. For instance, the 20 in the above examples indicates that your rim diameter is 20 inches. This is the measurement you get if you pass a straight line through your tyre centre, showing that your car tyre fits in a 20 inches (50 cm) rim.

Load index or tyre load

The load carrying capacity, load indexes, or load rating shows the maximum load your car tyre can carry in kilograms when moving at its maximum speed, but less than 210 kph. The above example represents your tyre load index by the number 99. This means that it can handle a load of up to 775 kilograms, according to the tyre load chart.

If you have another car tyre with a different number, you should check the tyre load chart for more clarification on the maximum load it can carry. The tyre load rating is usually based on several tests done by your car manufacturer under controlled conditions.

Speed index or tyre speed rating

The speed rating or index is represented by a letter. It is closely associated with the maximum speed of your car tyre when operating at its top load carrying capacity. In this case, your car speed index is indicated by the letter Y. This means that it can operate at a speed of 300 kph.

In simpler terms, the speed index refers to the maximum speed that your car tyres can handle. But, this is not to say that you must drive up to this high speed. Instead, you should adhere to the speed limit of each road you drive in Australia.

Manufacture date

Some car tyres also have numbers that indicate the month and year of manufacture. For instance, you may find that your car tyre has the number 09/17. This means that the tyre was manufactured in September in the year 2017. Manufacturers of car tyres usually indicate their manufacture date to help you correctly determine the right time to change the tyres.

Like other parts of your car, tyres also have an expiry date, meaning you need to replace them with new ones before that date. After around six years, the tyre rubber begins to deteriorate, and it's time for you to consider having new tyres to prevent accidents.

Other letters on car tyres

You may find other letters on car tyres, including:

• P - The letter P on car tyres means passenger and that the particular tyre is only meant to be used for passenger car types.

• LT - The letters LT are a shortened form of the words light truck, meaning that the tyre is specifically made for use on heavy duty and light pickup trucks.

• ST - In full, these letters indicate that it is a unique tyre. Tyres with these letters are made explicitly for towing trails with non-powered axels.

Tyre Tread Width Vs. Tyre Section Width

One of the most prevalent mistakes individuals make is thinking that the tread width and section width are the same, which is not the case. The tyre section is usually measured in millimetres and is the most expansive area from one sidewall to the other. Thus, a high number shows that a tyre is wide. For instance, a tyre with code P225/50R16 92V has a section width of 225 mm.

On the other hand, the tread width refers to the measurement between the inboard and outboard edges of a tyre tread design. Simply put, tread width refers to the width that connects the road. It is essential to understand that the tread width of a tyre differs among models and manufacturers, even if the tyres have similar widths.

Why Is The Tyre Aspect Ratio Important?

Aspect ratio is critical in tyre fitting and wheel alignment. The aspect ratio affects how your car's tyres respond to the road, take a corner, and its traction abilities. With a higher aspect ratio, your tyre flexes and absorbs shock, thus offering a more cushioned ride. However, the same flex can reduce your steering capacity and the car's handling ability when it takes a corner.

On the other hand, tyres with a low aspect ratio result in a less comfortable ride. This happens because the tyres hold less air causing a lot of vibrations through your car. However, a low aspect ratio with reduced flex gives you better handling and improved steering capacity. A low-profile tyre contacts the road more, leading to a firmer footprint and offering improved traction and cornering.

Different aspect ratios affect your car tyres response to the road and the power required to turn. Using tyres with varying ratios of aspect leads to alignment issues, more fuel usage, and unnecessary stress. You will find varying types and sizes of tyres for the modern car.‍

Note: You should only change the tyre width or aspect ratio, but not its diameter. This ensures that the tyre drives the way the manufacturer designed it.

Why Is The Load Index Important?

As mentioned above, load index refers to the maximum load capacity in kilograms that a particular car tyre can carry. Load index is considered together with the tyre's speed index. A tyre with a high load index number can carry heavier loads than one with a lower number. The load index of your tyre is critical to your safety. If you subject your car to more weight, it gets stressed and produces excess heat that compromises your car's integrity. Therefore, checking your car tyres load index is critical to ensure that you adhere to its limits.

How To Care For And Maintain Your Car Tyres

Now that you understand the meaning of the numbers on your car tyres and other related aspects, it is also essential to know how to take care of and maintain the car tyres. Let's look at some tips to help keep your tyres in good condition for a long time.

Maintain the correct inflation pressure

You should always ensure that you maintain the correct pressure in your car tyres. This ensures you have the proper tyre performance, enhances safety, improves durability, and saves on fuel. Therefore, ensure that you check your tyres at least twice a month using the correct tyre pressure gauge. The proper inflation pressure for your vehicle is indicated in your car's user manual, so look it up.

Under-inflation is the primary cause of a flat tyre and even significant cracking. It also increases rolling resistance, reduces load capacity, and causes excessive sidewall flexing. On the other hand, overinflating leads to stiffness that can lead to unwanted car vibrations. The contrast between the two shows why maintaining correct inflation pressure is essential.

Avoid excess tyre spinning

If your car gets stuck in mud, sand, or snow, you should avoid excessive tyre spinning as it could lead to overheating and irreparable damage. Instead, the best thing to do is to apply gentle forward and backward rocking motions to free your car.

Check the car tyres for wear and damages

You should replace your tyres once they reach 1.6 mm in tread depth. New tyres feature tread wear indicators appearing in the tread grooves when they reach 1.6 mm. Ensure you check your tyres for deterioration to avoid punctures and other damage to your car. You can also check the tyres for signs of wear to allow for timely repairs or replacement.

Perform the proper car tyre repair

If you see an issue with your car tyres, you should immediately perform the proper tyre repairs. This helps prevent further damages and losses. When mounting the tyres, ensure you follow the manufacturer's recommended mounting procedures. It's also advisable to leave any car tyre or any other repair work to a professional instead of doing it yourself.

Buying The Right Car Tyres

So now you know the meaning of your car tyre numbers. Thus, ensure that you check them whenever you are buying new tyres for your car. This will assist you in making the right decision concerning the right tyres that will ensure that your vehicle operates at its optimal level.

In addition, you should only buy your vehicle from a reputable car company in Australia. The right car sellers will also provide you with a car with the right tyres that will serve you for years without issues. Take time to research the different car sellers to find the one with the most positive reviews from their past clients. You do not want to make mistakes that might cost you.