What is Tyre Sidewall?

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The tyre tread, radial construction and tire sidewall all contribute towards the quality and durability of a tyre.

The tyre sidewall is the part of your tyre that touches your wheel rim. It's also where you'll find all sorts of useful information, such as the size and speed rating (eg: 195/65R15 91H or 205/55ZR16).

Most tyres have the brand name at the top and a little logo in a circle down near the valve stem. If it's not there, you can usually find it stamped into the side of the tyre, or sometimes on its centre cap. You'll also find the tyre width (from sidewall to sidewall) and aspect ratio (height vs width) down there.

For example, 195/62R15 has a width of 195mm and an aspect ratio of 62%. Higher numbers indicate more of an upright profile, taller in height than they are wide. The opposite is true for low numbers. These all come together to give your tyre's handling characteristic, known as the 'profile'.

You must be careful before fitting tyres to your vehicle to check the correct category. The role of tyre sidewall is important regardless of the tire size and wheel diameter.

You must keep a tab on the tread wear indicators to keep your tyres in good shape and condition. It is also recommended to read the service description for tyre pressure information, maximum inflation pressure, and maximum carrying capacity.

You can avoid tyre failure by properly inspecting your tyres for disappearing tread grooves and recommended tyre pressure.

Nowadays, radial ply construction tyres are manufactured to provide greater stability, performance and efficiency.

It is also recommended to check critical vehicle components to improve the performance of your vehicle

What is meant by tyre profile?

Now that you know what sidewall measurements mean, it's not hard to work out how different sidewalls react in different situations. A large sidewall will be soft and absorb bumps well, but with bad side-to-side stability. Smaller sidewalls will be stiffer, but less comfortable and more likely to twitch in quick directional changes - like when you're drifting. The sidewall design also influences the way that the tyre will react when it's moving. For example, a diagonal-lug pattern acts like little 'fins' that grip into the road surface to give better cornering stability at speed. On the other hand, straight-lug tyres are designed for good straight-line braking performance with high levels of comfort - but will lack grip at speed because there's no central locking mechanism to hold them together under load. The passenger car tyre is different from other types of vehicle tyres. You must also consider reading vehicle's manufacturer documentation and vehicle owner's manual to further increase the performance of your vehicle. Apparently, the types and quality of tyres seems a simple process but there are many things to consider before buying a one for your vehicle. You must check maximum speed rating, higher speed rating, maximum speed limit, load limits, load and speed capacity before making a purchase. Try to follow manufacturer recommendations if you are not familiar with the purchasing of tyres. Always try to find relevancy between your vehicle specifications and manufacture recommendations. You may bought tyres of that speed rating which matches speed capabilities of your vehicle. Tyre load index chart, speed index, load rating, lower speed rating, higher load index are some extra things to consider as well. If your tyre conforms all these ratings and indexes . Overloading your vehicle places stress on all the components of your car, especially the tyres. It may also result in increased fuel consumption over the time. Tyre's tread wear indicators can be followed to gauge the condition of tyres.

How to read your tyre sidewall markings

The tyre label on your sidewall is a lot more than just a bunch of codes that the manufacturer wants you to ignore - it's an important part of the technical specification for your tyre. It's also not as scary as it looks, even though there are quite a few numbers and initials there. In fact, most of them are important only to the specific brand or type of tyre. They'll look different from one brand to another, but tell you pretty much the same thing regardless. The markings include the below.

The tyre width and aspect ratio, so you know which wheel it'll fit.
The recommended inflation pressure for the tyre, including both minimum and maximum.
The load capacity of the tyre or the maximum weight it can hold when correctly inflated.
The speed rating that tells how fast a tyre can legally go before it becomes unsafe.

There are a few other codes such as a three digit code followed by a letter, for example: 195/65R15 91H is a size code (195mm wide) with an aspect ratio of 65% and a load index/speed rating of 91H. It refers to any set of tyres with those three specific markings.

The first number tells the width of the tyre, in millimetres

Aspect ratio is an indication of how "upright" or "aggressive" a tyre's profile is. The lower the number, the more upright it is, so 70% would be very 'squat' and have good straight-line stability but poor cornering grip at speed.

Higher numbers are more performance-orientated, with stiff sidewalls for better response to steering input. A 55% rating is quite common among standard road tyres and 45% at the lowest end will give you really sharp handling if your car can handle them.

When you get above 80% aspect ratio, you're looking at either snow or off-road tyres. Very high profile tyres (100% or more) are only found on 4x4s, where ground clearance is important. If you see anything like this, then there's a good chance the tyre will be marked with the letter 'L' - indicating it has an asymmetric tread pattern designed for left-hand drive vehicles

The next two digits tell you the load index (a measure of how much weight each tyre can hold at its recommended pressure) and speed rating (the maximum safe speed when correctly inflated).

The former tells you what sort of car it fits - which should mean that your speedometer reading will match the rated speed. However, different manufacturers may rate tyres to different standards, so always check if in doubt. Poor handling and driving puts a lot of pressure on the tyre's sidewall.

Tyre speed and load ratings in Australia

The higher the speed rating, the more stress it takes to make it work at high speeds.

Speed ratings are like tax brackets - they don't make much difference until you hit them. Standard passenger tyres start with a code of 82T, while the next bracket is 86H - which means you can safely exceed 90km/h. At 95km/h you hit 97S, at 100km/h it's 109R and at 110km/h you're looking at 112V to 114V.

To make this even more confusing, some brands will have different speed ratings for tyres in different sizes or widths. You could have a set of G78-14 tyres that are rated up to 150 km/h but another manufacturer may rate them differently depending on their overall size.

Also note that speed rating isn't just about speed - it's also an indication of how much load your tyre can carry when inflated to its maximum pressure. So if your car's manual says that your tyres should be inflated to up to 1.4 bar (which you'll find written on the sidewall as something like: "Max Pressure 1.4BAR"), and they're a 110SR-rated tyre, then they can carry a maximum load of 1320kg at that pressure

If you inflate them to their maimum and put more than that weight in the boot, there's a good chance they'll fail at some point. Take a look at WorkSafe Queensland for more information on tyre inflation.

Max Load Index is an indication of how much weight each tyre can hold when inflated to its maximum pressure, which also dictates how safe it is for each tyre to go beyond its recommended speed.