Tyre Size, Load Index & Speed Rating Explained
A tyre sidewall tells you far more than whether a tyre will fit your wheel. Understanding tyre size, load index and speed rating helps you choose tyres that suit your vehicle’s weight, performance requirements and manufacturer specifications. This tyre size explained breaks down those markings in plain English.
What Does Tyre Size Mean?
Tyre size refers to a combination of measurements and construction details that determine how a tyre fits and performs on a vehicle. You’ll usually find the size moulded into the tyre sidewall as a sequence such as 205/55 R16 91V.
Each part means something different:
- 205 – tyre width in millimetres
- 55 – aspect ratio, or sidewall height as a percentage of the tyre width
- R – radial construction
- 16 – wheel or rim diameter in inches
- 91 – tyre load index
- V – tyre speed rating
These figures work together. Two tyres may have the same rim diameter but very different widths, profiles or load capacities, so matching only the ‘16’ or ‘17’ on the sidewall is not enough.
What Does 205/55 R16 Mean on a Tyre?
For a common tyre marked 205/55 R16, the first number tells you the tyre is approximately 205 mm wide from sidewall to sidewall under specified measuring conditions.
The 55 is the aspect ratio. It means the sidewall height is 55% of the tyre’s nominal width. It does not mean the sidewall itself measures 55 mm.
The R identifies radial construction, which is standard on most modern passenger vehicles. Finally, 16 means the tyre is designed for a 16-inch diameter wheel.
For example, a driver replacing a worn 205/55 R16 tyre should not assume another 16-inch tyre will automatically be suitable. A different width or profile can alter clearance, rolling diameter, handling and other vehicle characteristics.
How Does a Tyre Size Chart Help?
A tyre size chart can help explain sidewall markings and compare tyre dimensions, but it should not replace your vehicle manufacturer’s specifications or professional advice.
Your vehicle’s approved tyre information may be listed on a tyre placard, commonly found around the driver’s door opening, or in the owner’s manual. Depending on the vehicle, more than one wheel and tyre combination may be approved.
If you are changing wheel diameter, tyre width or profile, the complete combination needs to remain suitable for the vehicle. Tyre Master Albury can check the relevant specifications rather than relying on guesswork based on the tyres currently fitted.
Once you know your correct size, you can also browse our full range of wheels and tyres to explore suitable options.
What Is a Tyre Load Index?
The tyre load index is the number immediately before the speed-rating letter. It represents the maximum load that an individual tyre can carry under specified conditions.
For example, in 205/55 R16 91V, the load index is 91. A load-index table converts that number into a maximum load capacity in kilograms.
The important point is that the number itself is an index, not a weight. A load index of 91 does not mean the tyre can carry 91 kg.
Your required tyre load rating depends on the vehicle and its approved specifications. Fitting a tyre with an unsuitable load capacity can affect safety and may mean the tyre does not meet the vehicle’s requirements.
This becomes particularly important with heavier vehicles, utes, SUVs, vans and vehicles regularly carrying passengers, equipment or other loads. Always check the required specification rather than choosing a tyre based on size or price alone.
What Is a Tyre Speed Rating?
A tyre speed rating is normally shown as a letter following the load index. In 205/55 R16 91V, for example, V is the speed-rating symbol.
The letter corresponds to a tested speed capability under specified conditions. Common ratings include H, V and W, although the appropriate rating depends on the vehicle and tyre application.
A higher letter is not simply an upgrade that every vehicle needs. Tyre construction and performance characteristics vary, and the replacement tyre needs to meet the specifications appropriate to the vehicle and comply with applicable requirements.
That is why it makes sense to have the complete tyre specification checked when buying replacements, rather than looking at tyre size alone.
Why Does Matching the Correct Tyre Size & Rating Matter?
Correct tyres support the way the vehicle was designed to steer, brake, carry loads and respond on the road. Changing tyre specifications without properly checking compatibility can affect more than fitment.
The correct specification matters for several reasons:
- Safety: Tyres need an appropriate load capacity and specification for the vehicle.
- Handling: Changes to tyre width, profile and construction can alter steering response and road behaviour.
- Clearance: Incorrect dimensions may create clearance issues around suspension components or bodywork.
- Rolling diameter: A significant change can affect vehicle systems and the accuracy of the speedometer.
- Compliance & warranty: Replacement tyres should meet relevant vehicle, tyre and legal requirements. Using unsuitable specifications may also create warranty issues depending on the circumstances.
For example, an Albury driver might find an inexpensive tyre online with the correct rim diameter but a different load index. Even if the tyre physically mounts to the wheel, that alone does not establish that it is appropriate for the vehicle.
How Do You Find the Correct Tyre Specification for Your Vehicle?
Start with the tyre placard and owner’s manual rather than simply copying numbers from a tyre already fitted to the car. Previous owners may have changed wheels or tyre sizes, so the existing setup is not always proof of the original or approved specification.
A tyre professional can check the vehicle details, current wheel setup and intended use before recommending replacements. This is particularly useful if you have aftermarket wheels, carry substantial loads or are considering a different tyre size.
For tyres in Albury drivers can have matched to the correct vehicle requirements, Tyre Master Albury can check the size, load index and speed rating before fitting.
If you are across the border, the team can also help with tyres in Wodonga and confirm your current tyre size and ratings before you buy.
What Else Should You Check on Your Tyres?
Knowing how to read the sidewall is useful, but the correct specification does not guarantee a tyre is still safe to use. Drivers should also keep an eye on tyre pressure, tread condition, uneven wear and visible damage.
Cracking, bulges, cuts or unusual wear patterns deserve attention because they can indicate tyre damage or an underlying wheel-alignment, suspension or inflation issue.
Once you understand what your tyre markings mean, our guide on how to check your tyres at home explains what Albury drivers can look for between professional inspections.
The key takeaway is simple: read the entire tyre specification, not just the rim size. Width, profile, wheel diameter, load index and speed rating all help determine whether a tyre is suitable for your vehicle.
Need new tyres but unsure which numbers you need? Contact the Tyre Master Albury team for tyre sizes explained. We can confirm the correct specification for your vehicle, check your requirements on the spot and help you choose and fit suitable replacement tyres for driving around Albury, Wodonga, Corowa and beyond.
Frequently Asked Questions
What does 205/55 R16 91V mean?
It describes the tyre’s main specifications. 205 is the nominal width in millimetres, 55 is the aspect ratio, R means radial construction, 16 is the rim diameter in inches, 91 is the load index and V is the speed rating.
Where can I find my car's correct tyre size?
Check the vehicle’s tyre placard and owner’s manual. The placard is commonly located around the driver’s door opening, although its location varies between vehicles.
Can I fit a different tyre size to my car?
Alternative sizes may be possible in some circumstances, but compatibility needs to be checked carefully. Wheel dimensions, tyre diameter, load and speed ratings, clearance, vehicle specifications and applicable regulations can all affect whether an alternative is suitable.
Is tyre load index important?
Yes. The load index identifies a tyre’s maximum load-carrying capacity under specified conditions, so replacement tyres need an appropriate rating for the vehicle.
What happens if the tyre speed rating is different?
A different speed rating means the tyre has a different tested speed capability and may have other construction or performance differences. Before fitting it, confirm that the rating is appropriate for your vehicle and complies with the relevant requirements.
Do all four tyres need to be the same size?
Many vehicles use the same tyre size on all four wheels, but some manufacturers specify different front and rear sizes. Always follow the approved specifications for your particular vehicle rather than assuming all four positions are identical.
