Tyre markings come in a mind-boggling mix of letters and numbers, along with measurements in millimetres or inches. You’ll find the markings we’re talking about on both sides of the tyre – usually referred to as the tyre’s ‘sidewall’.

Yep, I’m already confused…what now?

It helps to have a code-breaker on hand to make sense of the madness. Here we explain what it all means, using the code for one of the tyre types as an example:

225/60R17 99 T

The digits 225 refer to the section width (in mm) when the tyre is fitted to the recommended rim, inflated to the recommended pressure before it’s under load when attached to a car. You’ll either need to stick to the exact size the car comes with, or upgrade to a specific combination. On most cars you can upgrade to rims one or two inches bigger, requiring different widths and aspect ratios.

The number 60 is a percentage describing the tyre’s profile or aspect ratio. It’s the ratio between the tyre’s section height (distance from the wheel bead seat to the top of the tyre) and its section width. So in this case that’s 60%.

R stands for radial, which is the most common construction method for passenger car tyres. Radial tyres are more durable than older-style bias-ply tyres, and have lower road resistance which improves fuel economy.

The number 17 refers to the diameter (in inches) of the rim the tyre should be fitted to.

The number 99 is the load rating index, which tells you the maximum weight one tyre can carry (in this case, 775kg). Other examples include 89 (580kg), 92 (630kg), 94 (670kg) and 95 (690kg). Legally you need to make sure the tyres you buy have at least the load rating specified by your car’s manufacture.

T is the speed rating index and tells you the maximum speed you can drive the tyres at (in this case, 190km/h). Other examples are S (180km/h), H (210km/h), V (240km/h) and W (270km/h).

Extra ratings from the USA

Tyres sold in America must have a tread wear rating as part of the US Federal Government’s national (UTQG). If the same tyre is available here, you can use the information too – it’s printed on the tyre’s sidewall.

Under the system, a tyre’s tread wear is measured under controlled conditions involving an 11,500km drive on a specified test course, and compared with a “standard” tyre with a rating of 100. So a rating of 200 means the tyre should last twice as long as the standard model. So the higher the number, the longer a tyre should last.

The rating is purely based on controlled test conditions. Real-life wear depends on things like road surface, tyre pressure, wheel alignment and driving style. A tread wear warranty is a better measure of the expected life of the tyre.

Also part of the UTQG (and printed next to the tread wear rating) are:

• A traction rating that grades the tyre’s wet braking performance (AA, A, B or C, with AA being the best).
• A temperature rating, which tells you how well the tyre gets rid of heat (A, B or C, with A being the best).

These ratings aren’t very refined – just about every passenger tyre scores ‘A’ in both categories.

Special tyre designs

Directional tyres are designed to be fitted to the car so their tread pattern faces a particular way. This is usually marked with an arrow on the tyre’s sidewall.

It’s claimed directional tyres have better stability, but that’s something we haven’t reliably seen confirmed in our testing. Fitting them on the wrong side may affect the car’s handling and reduce the tyre’s life.

If you use this kind of tyre and don’t have a conventional tyre as a spare, remember that a directional spare will only fit one side of the car. If you have to use one on the wrong side, drive carefully and replace the damaged tyre as quickly as you can.

Asymmetric models (Outside/Inside) are designed to be fitted to the wheel rim so that a particular side (also marked on the tyre’s sidewall) faces outwards. This type of tyre can replace any of your car’s tyres if you need to use the spare.

M+S stands for Mud+Snow and this marking can be found on some SUV tyres. It’s not based on any performance tests, and just means the tyre meets certain design criteria.

Space-saver (narrower) spare tyres are found in some car models, instead of a full-size spare. If you have to use one, follow the instructions in your user manual. There’s likely to be a speed limit, sometimes as low as 70k/hr, and you’re only supposed to drive on it for a short distance to get you home or to the nearest tyre fitter – fine for inner city, but not so much for remote areas. 

Using it over long distances or at higher speeds can damage your car. If you are living regionally or in remote Australia, it will be best to demand a full sized tyre supplied with your car purchase – you shouldn’t expect to pay any more for a full sized car tyre with the right bargaining tactic.

The post How to read a tyre’s code appeared first on ÌÇÐÄVlog.

On this page:

• How we choose what we test
• How we test
• Test criteria explained
• Our test lab

We test a wide range of products – from espresso machines, vacuum cleaners and irons to tents, lawn mowers and tyre pressure gauges.

How we choose what we test

Tyre pressure gauges are a comparatively small product category, so, instead of surveying manufacturers, our buyers head straight out to stores, including auto accessory shops and online retailers, and purchase whatever they can find for us to put to the test.

How we test

Performance

Our tester checks the accuracy of the gauges at 10, 20, 30, 40 and 50psi against a calibrated high-precision gauge.

Ease of use

For ease of use, we assess:

• how well the gauge fits into the hand
• how easy they are to apply to the valve
• how easy the pressure is to read in daylight
• the instructions.

Test criteria explained

The overall score is made up of:

• Performance (70%)
• Ease of use (30%)

Our test lab

We maintain a lab that is up to date with the latest reference machines and calibrated measurement tools for our testers to bring you the right results.

The post How we test tyre pressure gauges appeared first on ÌÇÐÄVlog.

What makes a tyre ‘low profile’

Low-profile tyres have less sidewall than other tyres, and therefore more wheel. Driving (ahem) the trend towards low-profile tyres is, quite simply, their superior performance. A proportionally wider contact area generally improves roadholding and braking. A shorter sidewall is stiffer and less prone to deformation when exposed to lateral G-forces during cornering, which in turn sharpens steering response.

And some people simply like the look of low-profile tyres – a larger wheel size can impart a sense of sportiness or prestige to a vehicle.

Many carmakers offer their vehicles with two or three different OEM (original equipment manufacturer) wheel sizes within a range, typically increasing the wheel size and decreasing the tyre profile as specifications improve.

The risks of low-profile tyres

Australian roads can be pretty rough. Your tyres, an integral part of your car’s suspension system, are on the frontline when it comes to dealing with humps, potholes and other irregularities. As the tyre profile reduces, so does the tyre’s ability to absorb and cushion bumps, which results in a firmer and less comfortable ride. At the same time, the chance of impact damage to the tyres, wheels and other components goes up. 

Big car companies put millions into development and tuning, yet OEM options are not totally immune to these risks. Even more serious problems can occur in the aftermarket.

Because modern cars are engineered as complete systems, changing wheels and tyre sizes using non-OEM parts may upset the balance, and choosing sizes outside those specified on a vehicle’s tyre placard or service manual can be potentially dangerous or even illegal. Altering the overall diameter of your tyres can affect the calibration of your speedometer as well as your ABS, traction and stability control systems. State legislation governs the minimum and maximum sizes allowable for your type of car. If you want low-profile tyres, it’s worthwhile consulting an expert to make sure any planned changes comply with the laws in your particular state.

Should you get low-profile tyres for your car?

The upshot? If you’re considering changing your car’s tyre to a lower profile, you need to consider whether you want performance or comfort, or somewhere in between, and make sure any changes comply with the law. 

However, if this is the size tyre that is fitted to your car then you should definitely stick to this size. They’re not ‘performance tyres’, but just the best performing tyres for your vehicle.

The ’45’ in the tyre number is the aspect ratio – any tyre with an aspect ratio below 50 is generally considered ‘low-profile’. See How to read a car tyre for more.

The post Should you buy low-profile tyres? appeared first on ÌÇÐÄVlog.