By Samuel Okello
Tyres play a crucial role in the overall performance, safety, and efficiency of a vehicle. Understanding tyre information, codes, and sizes is essential for selecting the right tyres that meet your vehicle's requirements.
In this week’s write-up, we will delve into the details of tyre information, decoding the codes, and understanding tyre sizes.
TYRE INFORMATION
Tyre information provides valuable insights into a tyre's specifications, manufacturing selling points and performance characteristics. Here are the key elements of tyre information:
Tyre Manufacturer and Brand
The manufacturer's name and brand are usually imprinted on the sidewall of the tyre. Prominent tyre manufacturers include Michelin, Bridgestone, Goodyear, and Pirelli, among others. Each brand may have its own unique features and performance characteristics.
Tyre Type:
Tyres are categorized into various types, such as summer tyres, winter tyres (also known as snow tyres), all-season tyres, and performance tyres. Each type is designed to provide optimal performance under specific weather and road conditions.
- Tyre Construction:
Tyres can have different construction types, including radial, bias, and bias-belted. The most common type is radial, which uses layers of cords arranged radially from the center of the tyre. Radial tyres offer better grip, fuel efficiency, and handling compared to bias-ply tyres.
Load Index:
The load index indicates the maximum weight capacity that a tyre can support. It is represented by a numerical value, and a load index chart is available to determine the corresponding weight capacity. The higher the number, the greater the weight the tyre can handle.
Speed Rating:
The speed rating denotes the maximum speed at which a tyre can maintain its performance characteristics. It is represented by a letter code, such as "T" for 190 km/h or "V" for 240 km/h. Choosing a tyre with an appropriate speed rating is crucial for ensuring safety and performance. What tyre speed rating do I need?
Normal road-going cars usually require a tyre speed rating S or T - meaning the tyres are not safe to be used at a speed of more than 112mph or 118mph (180 - 190km/h).
UTQG Rating:
The Uniform Tire Quality Grade (UTQG) rating provides information about treadwear, traction, and temperature resistance. It consists of three digits for treadwear (higher number indicates longer wear), followed by two letters for traction and temperature resistance ratings.
- DOT Code:
The Department of Transportation (DOT) code is a unique identification number issued by the government. It includes manufacturing details such as the tyre plant code, size code, and production date.
DECODING TYRE CODES:
Tyre codes consist of a combination of letters and numbers that provide specific information about the tyre. Here's a diagrammatic breakdown of the most common codes:
The image above also outlines and identifies the different codes on the sidewall of the tyre as in the legend below;
- Manufacturer’s name or Brand name
- Model or Pattern Code
- Tyre Size, Nominal Section width(mm), Height to width aspect ratio, Rim diameter code
- Service description (Load Index + Speed Symbol)
- ECE R30 Conformity Approval Number
- EEC Noise Approval Number
- USA Dept of Transport Manufacturer’s code
- Date of Manufacture
- USA UTQG Quality Grades **
- USA Maximum Tyre Loading **
- USA Maximum Tyre Inflation Pressure **
- Denotes Tubeless Construction
- Safety Warning
- Direction of Rotation [Directional Tyres only]
- Outer (Inner) sidewall [Asymmetric Tyres Only]
- Extra Load: Denotes higher load capacity than standard tyre.
16a. “Reinforced” is an alternative marking to “Extra Load”
- TWI-Tread Wear Indicators- raised areas at the base of the tread grooves to serve as a visual warning of when the tyre is approaching or at the minimum legal limit.
TYRE SIZE:
The tyre size is indicated by a series of numbers, such as 205/55R16. Here's what each number represents:
205: Tyre width in millimeters
The first three figures included in the tyre size information is the width of the tyre from sidewall to sidewall - measured in millimetres.
55: Aspect ratio.
This is the height of the sidewall as a percentage of the tyre width). It's referred to as an aspect ratio because a percentage of the tyre width - so in this case, the sidewall height is 50% of the width.
R: Radial construction
Today, most tyres have a 'radial' construction - a term used to describe how the fibre cords inside the tyre are arranged when it's manufactured. In rare instances, you may also see 'B' (describing a 'bias belt' construction) - or 'D' (a diagonal construction).
16: Rim diameter in inches
The final 2 numbers on a tyres size marking indicate the rim diameter that the tyre is designed for. This measurement is in inches.
TYRE SIZES
Understanding tyre sizes is crucial when replacing or upgrading your tyres. Here are a few important points to consider:
Plus-Sizing:
Plus-sizing refers to installing larger diameter rims with lower profile tyres. This can enhance the appearance and performance of the vehicle, but it's important to maintain proper overall tire diameter to avoid speedometer errors and potential suspension issues.
Load Range:
For specific applications, such as light trucks, the load range identifies the maximum weight capacity and inflation pressure of the tyre. Load range codes vary from A (lowest capacity) to F (highest capacity).
A LITTLE MORE ON EU TYRE RATINGS
As well as seeing EU safety approvals on a tyre sidewall, important information about your tyre's performance should be included on a sticker when your tyre is new - and many retailers/manufacturers show this information on their website too.
An EU tyre sticker looks like this:
Figure 1. EU Tyre Sticker showing fuel efficiency, wet grip and noise ratings per EU standards
Fuel economy rating.
The section in the upper left part of the tyre sticker rates fuel economy - useful information when you consider that your tyres can account for up to 20% of your fuel consumption. Fuel economy is rated from A (green) to G (red) - although the D-rating is not used for passenger cars.
Wet grip rating
The upper right part of the sticker shows a wet grip rating. Wet grip is rated from A to F (although D and G are not used for passenger cars) - and it makes a massive difference to your ability to stop. On a passenger car applying full brakes at 80km/hr. - A-rated wet grip tyres will stop you up to 18 metres shorter than a set of F-rated tyres.
Noise rating
Finally, at the bottom of the sticker there's a noise rating - showing the noise impact your tyres will have on your surroundings. A single black wave coming from the speaker icon indicates the tyre is 'quiet' (3dB or more below the EU limit) - 2 black waves is considered 'moderate' (between the EU limit and 3dB below) - and 3 black waves is 'noisy' (anything above the EU limit).
GETTING YOUR TYRE PRESSURE RIGHT
Even the correct tyres can be dangerous or negatively impact your fuel economy if they're not inflated properly - so it's worth taking a moment to consider tyre pressures. To find out your car's intended tyre pressures, you should check your handbook - or look just inside one of your car's front doors for a sticker like this:
CONCLUSION
Tyre information is there to let you know if your tyres are fit for purpose. You might not consider it, but there's a perfect tyre for you out there - based on your vehicle, the type of driving you do, the load you carry - and a host of different factors.
For virtually all of us, the tyres your retailer picks will be perfect - but if you've got any specialist needs (a modified car, a car you use for offroad days) then you might need to do a little research to make sure your choice is right.
Make sure you're running the correct tyre size, with the correct maximum speed rating - and always ensure the load index is correct for the kind of driving you’re doing. Tyres are serious business - always seek professional guidance when you're buying - and don't be tempted to cut corners.
OKELLO SAMUEL
B.Eng. Automotive and Power Engineering
Technical Director
S-Line Motors LTD
Plot 6, Ojara Close, Mbuya
https://goo.gl/maps/bEGeVEN7tUVTqHnu8
0779745722 / 0708000888