The other article in this week’s newsletter deals with tyres and road safety. The massive anti-dumping duty imposed on imported tyres (mainly from China) will result in the disappearance if budget tyres and the worry is that cash-strapped motorists will now continue driving on their old, worn tyres as they cannot afford to replace them.

This is a legitimate concern but ultimately tyres are a safety-critical item and if money has to be saved, the one place it shouldn’t be is on tyres. It is worth forgoing a couple of luxuries or niceties to invest in a new set of tyres when needed. When that times comes, to replace your tyres, here is a quick guide of what the different specifications written on the sidewall of the tyre means, and why it’s important.

The size of a tyre is pretty self-explanatory, so we will not go into much detail about that, other than what is stated in the summary below:

(To give credit where it is due, the information in the sections about Load Speed and Speed Rating come from  Tirebuyer.com, and the sections from DOT Rating onwards from United Tyres  and Continental Tyres )

Speed Index/Rating

Tyre speed ratings are set by the tyre manufacturers and are an indication of the tyre’s maximum speed capability in ideal conditions. The tyre load index rating communicates how many pounds a tyre can safely carry. Put together, they make up the service description.

Knowing this service description information is highly recommended whenever you’re replacing Original Equipment (OE or factory) tyres. Even if you don’t plan on pushing limits in speed or load categories, matching or improving the speed rating and load index of your factory tyres will help keep your vehicle’s performance characteristics consistent.

 

 

How to find tyre speed rating

 

Service description on doorjamb

In the doorjamb image above (belonging to an Audi A3), the car’s tyre information is: 225/45R17 94H. In this example, 94H is the service description, with the 94 indicating load index, and the H indicating speed rating.

You can also find this information printed on the sidewall of all tyres.

Speed rating is established under controlled testing where – once again, under optimal conditions – the tyre is verified as capable of safely running at (up to) the indicated miles per hour. Heavily worn, damaged, punctured, or repaired tyres would all be considered sub-optimal, and no longer capable of safely accomplishing their max speed rating.

 

 

Speed Rating Chart

Going back to our Audi, the H speed rating is equal to 130 miles per hour (210 Km/h), meaning that under optimal conditions, the tyre can perform at speeds up to 130 mph (210Km/h. The speed rating doesn’t imply the vehicle can drive that speed, but the tyres are capable of supporting the car at that speed.

 

 

Tyre Load Index

The tyre load index rating communicates how many pounds a tyre can safely carry.

Going back to the Audi example, the car’s service information is: 225/45R17 94H. 94 indicates the load index. Referring to the tyre load rating index chart below, the number 94 translates to a load-carrying capacity of 1477 pounds (per tyre).

While you’re probably unlikely to approach the top speed rating of your tyres, pushing load index ratings is more common, especially when it comes to hauling and towing with trucks and SUVs. Use the chart below to understand the weight limitations of your vehicle’s tyres. Additional attention should be paid to the vehicle’s hauling and towing limits, which are set by the manufacturer and involve tyre capacity, as well as drivetrain and other considerations. Check your vehicle owner’s manual for details.

 

 

Tyre Load Rating Chart

Note: You should never replace your tyres with a lesser speed and load rating than the original equipment tyres. 

You can replace a tyre/your tyres with a high-speed rating and load rating.

 

 

Simply put, the load index is the weight that particular tyre can safely carry. A load rating of 87, equates to 545kg on each wheel. If we were to multiply this by the four wheels, the weight of the vehicle should not exceed 2180Kg.

DOT Code

DOT stands for the US Department of Transportation and its code is usually a combination of 10-13 digits and letters.

Image source: discounttyre.com

 

  • Plant code.
    Every manufacturer’s plant in every country has its own 2-3-symbol code. Tyre Safety Group provides a database with all plant codes available, so you could check this information.

 

  • Tyre size.
    The two following symbols show tyre size. However, this code translation isn’t for customers. It concerns manufacturers and is mostly moulded for them. These codes make it easier for them to find tyres that have to be recalled.

 

  • Manufacturer identity number.
    This 3-4-symbol code is moulded solely for manufacturers’ purposes: they identify a tyre by this code and recall it if necessary.

 

  • Date code.
    The main thing for the driver is the tyre’s 4-digit date code. The first pair of numbers means the week of manufacture, and the second pair indicates the year. With reference to the diagram above, the tyre was made during the 10thweek of 2016.

The date code is vital for any driver, as it says precisely how old the tyre is. A tyre lasts for a maximum of 10 years, no matter whether it’s ridden or stored in your garage/a store. Be sure when fitting new tyres that they haven’t spent several years on the shelf. Most manufacturers recommend buying tyres once your old set turns 6 years old.

 

 

Uniform Tyre Quality Grading (UTQG) code

All decent tyres will have the UTQG code which shows estimates of 3 tyre characteristics based on the tests conducted by a particular manufacturer. This is a requirement on all passenger vehicle tyres (greater than 12”) in the US. If your tyre does not display these, there is a good chance it’s a poor-quality tyre on which no tests have been performed. Stay very far away from it.

 

UTQG code. Image source: kaltyre.com

 

  • Treadwear.
    This rating is a 3-digit code, where 100 is standard wear, 200 – twice as much, etc. This is an estimate that is based on the tests run by the respective manufacturers. In extreme conditions or improper maintenance, the index may become irrelevant.

 

  • Traction.
    This quality is evaluated in letters: AA, A, B, C, from the best to the worst. Traction test assesses stopping a vehicle on wet asphalt and concrete, measuring the coefficient in g (g-force).

 

  • Temperature resistance.
    This characteristic is also measured in letters: A, B, C. It shows up to what speed a tyre can safely dissipate heat, and is measured in mph. A goes for over 185 Km/h, B – 160-185 Km/h, and C – 135-160 Km/h.

 

 

Choose Tyres Carefully

Your tyre choice determines the quality of your ride, as well as the speed and load of your vehicle. It also indicates whether you have wasted your money on nothing or the tyre will serve you for years. If your tyre choice is wrong, it can also jeopardize yourself and your car. The wrong size can become troublesome for your vehicle functions, and tyre age can cause tyre failure. So, make sure you have a serious attitude towards choosing the best tyres for your vehicle when you go to a tyre shop