We’ve all heard the phrase “if the shoe fits”. Of course, it’s not supposed to be taken literally, but when it comes to cars, it’s vitally important to make sure your vehicle is equipped with the correct rubber fitted to its wheels. If this shoe doesn’t fit exactly, you could be wasting your money buying tyres you don’t need or worse, dangerously fitting your vehicle with the incorrect tyres.
Whether you’ve picked up a puncture or you’ve measured your tread and it’s not up to scratch, you’ll need to understand the alphanumeric code on the side of your tyres.
How Do Tyre Sizes Work?
The size of a tyre refers to the height and width of this rubber case that’s going to (once you understand sizings) snuggly fit around the wheel of your car. If you’ve ever browsed for a new car, you’ll have most likely seen – especially if it comes with alloys – a ‘wheel size’ listed in inches. Naturally, this size directly correlates to the size of tyre that the car will need.
You may or may not even know the size of the tyres on your own car, but should you ever need an emergency change (like at the roadside, perhaps) you will want to know exactly what your car is packing.
Luckily, this information is hidden in plain sight, right on the sidewall of the tyres themselves. Take a closer look at any tyre and you will see a series of numbers. Unless you know how to decipher them, these numbers might as well be written in hieroglyphics. That’s why Scrap Car Comparison is on hand to explain tyre sizes and show you what they all mean.
How to Check, Measure & Read Your Car’s Tyre Size
Now that you know where to look, let’s talk numbers.
Using “205/55 16” as an example size, we can break down what each number means:
- 205: This is the width of the tyre. Simply put, it’s how wide the tyre is in millimetres.
- 55: This is the aspect ratio. You might have heard this term used in TV or film conversations, and the basic principle is essentially the same. It’s a percentage indicating the height of the tyre from bead* to tread in relation to the tyre’s width.
*The ‘bead’ is the edge of the tyre that sits on the wheel.
- 16: This is the rim diameter. Like we mentioned earlier, each wheel rim (alloy or wheel trim) is measured and listed in inches. This size does not include the tyre.
How to read your car’s tyres
The eagle-eyed amongst you will have noticed that there are actually more figures on the sidewall of your tyre. Those are less about measurements and more about your tyre’s limitations, so they’re important to understand, too.
Here’s what they mean, with a diagram from Bridgestone:
- R: This is the method of tyre construction. If you’re the average car driver who just wants to keep your car on the road safely, this probably won’t concern you too much. In this instance, the ‘R’ stands for Radial Ply Construction, the most common method for regular passenger vehicle tyres. If you don’t see an ‘R’ then your tyre is most likely a cross-ply construction instead. This type of tyre is cheaper to produce, but is more rigid, meaning it’s less comfortable to ride on and can also increase fuel consumption.
- 91V: This is the maximum load & speed. This is where things get a little more complex and you’ll have to do a bit of your own decoding based on your tyre’s numbering.
A load index rating of 91 means that this particular tyre can withstand a maximum load of 615kg.
A tyre with the speed symbol ‘V’ can reach speeds of 149mph (240kmh) before it begins to become unfit for your driving purpose.
Please note that these ratings are also subject to the tyre being in good condition and operating at the correct pressure.
What Size Tyres Do I Need For My Car?
Now that you have all the information you’ll need to figure out what size tyre you need, it’s time to take a look at your own car and make a note of the figures.
Whilst you’re down there, make sure you measure the tread on your tyres. You may find out that you need more replacement rubber than you expected.
Once you have the details, take a look online for a tyre size calculator. These are usually hosted by retail sites that will suggest (read: try to sell you) the ideal tyre for your vehicle.
How to pick the right tyres for my car
To get the right tyres for your car will depend on a number of factors, ranging from what you drive to when you’re driving. To get the right tyres for your car, you’ll need to know what code of tyre you’re looking for. This can be found in your vehicle’s owner manual and is also usually found inside the driver’s door on the body of the car. It may look like a confusing set of numbers – and there’s also often more than one suggested. Once you’ve read this guide you should be much more knowledgeable and know what your car needs, however, or if you’re still stumped there are many online resources to help.
The time of year you’re looking for tyres will change what ones you need, as well. If you’re planning to drive in the winter months then winter tyres are the obvious recommendation. While some may think this is just a ploy by garages and tyre companies to get more money out of you, they do provide superior grip during the inclement weather.
How to Check a Bike’s Tyre Size
Car drivers and motorcyclists may not always get along as they attempt to live together in harmony, but in terms of tyre sizes, they’re not that different after all.
Here’s how to read motorbike tyre sizes, breaking it down using the example measurements of ‘120/70 – 12 51 S’.
- 120: Tyre width in millimetres.
- 70: Tyre aspect ratio.
- 12: Wheel rim diameter.
- 51: Tyre load index.
- S: Tyre speed symbol.
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