Calculate Tyre Size
Tyre size chart
Have you ever wondered what the markings on the sidewall of your tyre mean? Your tyre’s sidewall markings are a tyre specification guide containing important information about size, load, and much more. This indicates the nominated tyre size for your vehicle from the manufacturer. Be careful if changing away from the nominated tyre size, as this could make your vehicle un-roadworthy.
Learn how to read tyre codes and your tyre size with the tyre size calculator.
Vehicle placard tyre size
Tyre size explained
Tyre dimensions
Width:
The section width of your tyre in millimetres, from the inner sidewall to the outer sidewall. Example: 195mm
Aspect Ratio:
The height of your tyre from the base of the tread to the rim, as a percentage of the tread width. Low profile tyres have smaller aspect ratios. Example: The height of this tyre is 65% of its width.
Tyre Construction:
The method used to construct your tyre. Example: R, for radial ply construction. This is the most common method of construction for passenger tyres.
Rim:
The diameter of the wheel rim in inches. If you are buying wheels for existing tyres, this is the size you will need. Example: 15 inches.
Load Index and Speed Symbol
The maximum load capacity under which your tyre can safely operate, and at what speed. This is subject to the tyre being in sound condition, correctly fitted, and with the recommended inflation pressure. Example: 91 V
How to find your tyre size?
Knowing how to check tyre size is straightforward. You can find your tyre size by examining the sidewall of the tyre, referencing your vehicle's owner's manual, or locating the placard inside the driver’s door jamb. Accurate tyre size ensures optimal performance, safety, and fuel efficiency.
If still uncertain about your tyre size, contact your local Bridgestone store who will be able to assist with all your tyre needs.
Read your tyre size
OD:
The overall diameter of your unloaded tyre in mm.
Type Definitions:
An abbreviation providing information about the type of your tyre.
Examples:
RFT – Run Flat Technology
MOE – Mercedes Original Equipment
LRR – Low Rolling Resistance
RBT – Raised Black Letters Tubeless
OWT – Outline White Letters Tubeless
RWT – Raised White Letters Tubeless
LWT – Line White Tubeless
TT – Tube Type
TL – Tubeless
XL – Extra Load
LT – Light Truck construction
N* - Porsche specification
☆ – BMW spec
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Frequently asked questions
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Can I change my tyre size from the manufacturer recommendation?Changing tyre size is possible, but it must be done within legal and safety limits in Australia. Incorrect sizing can affect braking, handling, speedometer accuracy, and vehicle safety systems, and may impact insurance or roadworthiness.
Bridgestone Select Tyre & Auto can help ensure any alternative tyre size is safe, compliant, and suitable for your vehicle before installation.
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Why is using the correct tyre size important?
Using the correct tyre size ensures optimal vehicle safety, braking performance, fuel efficiency, and stability control operation. It also prevents uneven wear and ensures your vehicle performs as intended by the manufacturer.
Bridgestone Select Tyre & Auto ensures your tyres are correctly matched to manufacturer specifications for safe and reliable driving.
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Where do I find my correct tyre size?
Your correct tyre size is listed on the tyre sidewall, the vehicle tyre placard (usually inside the driver’s door jamb, glovebox, fuel cap, or under the bonnet), and in your owner’s manual.
These sources provide the manufacturer-approved tyre specifications, and Bridgestone Select Tyre & Auto can assist in verifying the correct size for your vehicle before fitting.
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How do I calculate my tyre size using a tyre size calculator?
A tyre size calculator helps you identify the correct tyre dimensions by converting the markings on your tyre sidewall or vehicle details into standard tyre sizing. It ensures you select tyres that match your manufacturer’s specifications for width, profile, rim diameter, load, and speed rating.
This ensures your replacement tyres remain safe, road-compliant, and correctly matched to your vehicle, with Bridgestone Select Tyre & Auto able to help confirm the correct fit.
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What do the tyre numbers mean?
The tyre sidewall, located between the wheel rim and tread, displays tyre numbers and letters that indicate the tyre’s size, construction, load capacity, and speed rating. These markings help you select tyres that fit your car safely and perform reliably.
For example, a tyre marked 205/55 R16 91V means:
- 205 = tyre width in millimetres
- 55 = aspect ratio (sidewall height as a percentage of width)
- R16 = radial construction and wheel diameter in inches
- 91V = load index and speed rating
Always check your vehicle’s tyre placard or owner’s manual, and use the Bridgestone tyre size calculator to confirm compatibility and ensure optimal performance.
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Width
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Aspect
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Rim Size
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Load
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Speed
The section width of your tyre in millimetres.
The sidewall height measured from the base of the tread to the rim. This number represents a percentage of the tread width. Low profile tyres have smaller aspect ratio percentages.
The diameter of the wheel rim in inches. This is the size you will need to choose if you are buying wheels for an existing tyre.
The maximum load capacity at which your tyre can be safely operated. This is subject to your tyre being in sound condition, correctly fitted and inflated at the recommended pressure.
A code indicating the speed at which your tyre can be safely operated. Again, this is subject to your tyre being in sound condition, correctly fitted and inflated at the recommended pressure.
