Tyre Basics 101 for the daily driver

Tyre Basics 101 for the daily driver

Tyres are essential to every car. Here’s a cheat sheet on the tyre basics that you need to know.

Tyres are like shoes for a car. They cushion the car from impacts from the road, keep the body off the ground, and most importantly, provide the traction needed to go, stop and steer.

Much like shoes however, there can be a bewildering array of brands and models to choose from. Take a shoe brand like Asics, for example; they produce many different models of shoes; Metaride, Gel Kayano and Gel Nimbus, to name a few, all with differing use-cases.

Similarly, tyre companies make a variety of products for different car types and driving styles, and this information can be found on the tyre’s sidewall – for example, Bridgestone Potenza Sport, Davanti DX390, Pirelli Cinturato P7, etc.

Now that we know the brand and model of tyres our car came with, the next item is tyre size.

Size matters

We wouldn’t walk into an Asics shop, say, “I wanna buy Gel Nimbus,” and simply stand there blinking at the sales assistant, expecting to be given the right pair of shoes for our feet; we need to know the specific shoe size that works best for us. Similarly, it would be better to know the correct tyre size for your car before going shopping, but luckily unlike shoes, you don’t need to take off a tyre to check its size; all the information you need is written right there on its sidewall:

There are various shoe sizes as well as shoe widths. So for a perfect fit, we need to choose the right size (length) and width of shoe to match our feet, for example, US 11D.

Things are pretty similar in the world of tyres. Look for a set of numbers on our tyre-sidewall that read something like this: 

Analogous to a shoe’s length is the first number – 245 – which represents how wide the tyre is (245mm in this example).

Analogous to a shoe’s width is the second number – 50 – which represents how tall or thick the sidewall is in relation to the tyre’s width (50% of 245mm).

R stands for ‘radial’ – most tyres today use a radial construction method, as opposed to bias-ply construction, which is now used generally for classic cars.

19 tells us the rim diameter that the tyre is mounted on, in inches.

The last number and alphabet, 105W, represents the load and speed rating of the tyre respectively, but can be ignored for now for simplicity’s sake.

To recap, in the same way we’d walk into an Asics store and say, “I’d like a pair of Gel Nimbus in US 11D please,” we’d pull up to a tyre shop and say, “I’d like to buy a pair/set of Pirelli Cinturato P7s (or wthatever brand/model of your choosing) in two-four-fivefiftyR nineteen please.”

Or “one-nine-fivefifty-fiveR fifteen“, or “two-two-fiveforty-fiveR seventeen“, or whatever is appropriate to your car.

Now that we know more about tyres, tyre sizes, and the appropriate tyre shop lingo, let’s look at how to choose a suitable set of replacements.

If it ain’t broke …

If you’re happy with the way the existing tyres felt and performed, and how long they have served you, simply purchase another set of the same model and size from the same manufacturer. Keepin’ it simple, as they say.

But what if it isn’t available any more?

Sometimes, a tyre manufacturer may discontinue a particular tyre model to make way for a successor, or due to low market demand.

So in our example from earlier, let’s assume that our car currently wears Bridgestone Turanza T005A 185/65R15 tyres. Let’s also assume that, for whatever reason, they are not currently available for purchase. What is one to do?

The hassle-free answer of course, is to use AutoApp, whose friendly Service Ambassadors would only be too happy to recommend the perfect replacement tyres for your car.

However, if you’d like to do the homework to know more about what you’re buying, we’d suggest Googling for tyres that promote the tyre characteristics that are priorities for you, such as:

  • Ride comfort and noise
  • Grip and handling
  • Safety (dry & wet stopping distances, and aquaplaning resistance)
  • Recommended pricing
  • Size availability

It also wouldn’t hurt to check out test results and reviews both from tyre review and car magazine sites, as well as users’ testimonials. That said, you should take the latter with a pinch of salt, as these are entirely subjective, and depending on geography, those drivers’ usage patterns and weather conditions likely differ from ours here in Singapore.

How about a +1 upgrade?

Despite everything discussed so far, it’s not an absolute necessity to use the exact same tyre size. Sometimes a tyre brand and/or model you want to switch to might not be produced in your existing size; sometimes the tyre shop you visit might not have your size in stock; and sometimes you might want to try a slightly different width.

A wider tyre offers more rubber on the road, which usually translates to better grip in both dry and wet, with minimal-to-no increase in aquaplaning, as well as slightly shorter braking distances due to better grip.

Using a slightly different size from stock is perfectly fine, as long as the overall diameter of the wheel+tyre remains the same. If it differs too much, your speedometer and odometer readings will be affected.

Of course, the diameter can be calculated using geometry, but just in case you’ve given back all mathematical concepts to your secondary school teacher and now only know π of the apple or chicken variety, there are handy tyre calculators online that can help you quickly get those numbers.

Using the one on 1010tires.com, we can quickly check the next appropriate size for our car, based on our 185/65R15 example. Here’s how to use it:

Firstly, enter current tyre size under “Tyre Size” tab” and click ‘Convert.’

Next, look at the “green rows” in the ‘Results’ section of the same page. These green rows represent various tyre sizes that are closest to the one you originally selected.

In our example, the next nearest (and slightly wider) tyre size is 205/60R15. This size represents a 20mm increase over the stock 185-width tyre, and could very likely be a suitable candidate for a +1 upgrade.

Finally, check with the staff at your preferred tyre shop to confirm that your car’s stock factory rims can accommodate the slightly wider tyre (usually they can).

Of course, if you’re changing to a different set of rims for whatever reason (aesthetics, performance, or damage), you may well have to change tyre sizes too. Just bear in mind that if you’re using larger rims, you’ll consequently need tyres with a thinner sidewall in order to maintain that crucial consistent overall diameter.

So, that’s pretty much all you need to know for Tyre Basics 101, and we hope you find this guide useful.

When colleague and fellow performance-enthusiast Jon swapped to larger rims on his family car, he also had to switch tyre sizes from 215/60R16 to 225/50R17 – because he fancied his family’s Mitsubishi Grandis to be an Evo. Roll on over to our Tyres 102 article if you’re like Jon.

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