Every tyre carries a code on its sidewall that tells you exactly what it is and what it can do. Once you know how to read it, buying the right tyre for your truck becomes much easier, and you avoid costly mistakes such as fitting a tyre that cannot carry your load. Let us take a common truck size, 315/80R22.5, and break it down.

The size code, step by step

• 315 is the width of the tyre in millimetres, measured from sidewall to sidewall.
• 80 is the aspect ratio. The sidewall height is 80% of the width. A higher number means a taller sidewall.
• R means radial construction, the standard for modern truck tyres.
• 22.5 is the diameter of the rim, in inches, that the tyre is made to fit.

So a 315/80R22.5 is a wide, tall radial tyre designed for a 22.5 inch rim, a very common combination on heavy trucks and trailers.

Load index and speed rating

After the size you will usually see something like 156/150L. This is just as important as the size itself.

• 156/150 is the load index. The first number applies when the tyre is fitted on its own (single), and the second applies when it is fitted in pairs (dual). Each number corresponds to a maximum load in a standard load index chart.
• L is the speed rating, the maximum speed the tyre is designed for when carrying its rated load.

Always match or exceed the load index and speed rating your vehicle maker recommends. For trucks that run fully loaded on long hauls, this is not optional. An under-rated tyre can overheat and fail.

Other markings worth knowing

• Tubeless or tube type. Most modern 22.5 inch truck tyres are tubeless. Check what your rims are designed for.
• Manufacturing date. A four digit code, often inside an oval, shows the week and year the tyre was made. For example, 2324 means the 23rd week of 2024. Rubber ages even when a tyre is not used, so fresher is better.
• Maximum pressure. The sidewall shows the highest pressure the tyre can safely hold. This is not your everyday pressure. Follow your vehicle or fleet guidelines for the right inflation for your load.
• Axle position. Some truck tyres are designed for steer, drive or trailer axles. A steer tyre is built for precise handling, while a drive tyre has a deeper, more aggressive tread for grip. Using the right tyre in the right position helps with safety and wear.

Why the right size matters

Fitting the wrong size can affect braking, handling, speedometer readings and how the load is shared between tyres. On dual wheels, the two tyres in a pair should be the same size and similar in wear, otherwise one tyre carries more than its share and wears out early.

If you are unsure, the size recommended by your vehicle maker is usually printed in the owner's manual or on a plate in the cab, and your current tyres will show their size on the sidewall.

Common truck tyre sizes

Alongside 315/80R22.5, you will often see sizes such as 385/65R22.5 for trailers and 13R22.5 for heavy-duty work. Each has its own job, so match the tyre to how and where your truck operates: long highway runs, mixed roads or tough site work.

A quick buying checklist

• Confirm the size from your current tyre or vehicle documents.
• Check the load index and speed rating match or exceed the recommendation.
• Choose the right tyre for the axle position.
• Look at the manufacturing date.
• Ask about fitting, balancing and alignment when you buy.

Not sure which size you need?

Send Oseas a clear photo of your current tyre sidewall and we will help you find the right match. Browse our truck and commercial Tyres online and tap Enquire Now, or call +233 24 354 3747 or +1 (347) 575-7454.