What do the numbers on a tyre mean?
If you look at the sidewall of your tyre, you'll see a sequence of numbers and letters, such as 225/45 R17 91V. Here is how to decode it:
225
Tyre Width
The width of the tyre in millimetres.
45
Aspect Ratio
The height of the sidewall as a percentage of the width.
R17
Rim Diameter
R = Radial construction. 17 = Fits a 17-inch wheel rim.
91
Load Index
Maximum weight capacity per tyre (91 = 615 kg).
V
Speed Rating
Maximum safe speed for the tyre (V = 149 mph).
Frequently Asked Questions
How do I find my tyre size without looking at the tyre?
You can usually find your tyre size in your vehicle handbook, on a sticker inside the driver's door jamb, or inside the fuel filler flap. However, the most accurate way is to check the sidewall of your current tyres.
Can I fit different tyre brands or sizes?
Different sizes: It is illegal and highly dangerous to mix different tyre sizes (or construction types, like radial and cross-ply) across the same axle. While some cars are designed with wider tyres on the rear axle (staggered fitment), you should never deviate from the manufacturer's specified sizes.
Different brands (same axle): Technically, you can mix different brands or tread patterns on the same axle as long as the size, load index, and speed rating match. However, it is strongly advised against. Different tread patterns grip the road differently, which can cause unpredictable handling and braking, especially in wet conditions.
Different brands (different axles): It is acceptable to have one brand of tyres on the front axle and a different brand on the rear axle, provided both tyres on each axle are identical.
What is the load index on a tyre?
The load index is a number (e.g. 91) that indicates the maximum weight each tyre can support. Load index 91 = 615 kg per tyre. Always fit tyres with a load index equal to or higher than the manufacturer's minimum specification.
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