How Are Tyres Classified?

What is the most important of an automobile? From Scooters to Trucks.

Let me know your opinion in the comments section of this blog.

For me, an automobile is only as good as the engine and the tyres it comes with. Without these 2, a vehicle is barren. Sure there are other components that are essential to ensure an automobile does its job, but none of these components are complete without the engine and the tyres.

In this blog I am going to talk about one of the most important component of an automobile - TYRES.

Modern pneumatic tyres are essentially made of synthetic rubber, natural rubber, fabric, wire, carbon black and additional chemical compounds.

Tyres consists of a body and a tread.

Body is the section which contains specific quantity of compressed air and tread is the outer section that is responsible for providing traction with a surface.

But how do you understand which tyre is suitable for your vehicle?

To make it easier, all tyre manufacturers mentioned certain alphanumeric information on the tyre wall.

In this blog, I am going to write and show a very comprehensive detailed information and how to understand tyres and which one will be suitable for your vehicle.

First let's understand the measurements stated below,

A - Rim Diameter. It is the diameter of the wheel rim measured in inches(in).

B - Tyre Width. The overall width of the tyre measured in millimeters(mm).

C - Profile/Aspect Ratio. The profile is essentially the depth of the tyre sidewall. It is measured from the wheel rim to the outer circumference of the tyre. It is certain percentage of the tyre width.

That was easy right? Who knew?

Now let's take a look at how these tyres are classified for different vehicles and different usage conditions.

If you seethe image above, the tyre has certain numbers and alphabets. These are the keys to a huge amount of information which will help us understand the purpose of a tyre.

A - This is the most obvious information. It is the name of the tyre manufacturer, which in this case is Continental

B - This is the section width of the tyres. It is measured in millimeters. In this image the section width of the tyre is 225 mm.

C - Aspect Ratio/Profile. This is the height from the base of the tread to the rim. The number represents a percentage of the tread width. In the image shown above, the profile or aspect ratio of this Continental tyre is 50%

D - This is means tyre construction. R stands for Radial Ply Construction and these days almost all major tyres are manufactured in this manner.

E - The number '17' here indicates the diameter of the wheel rim. It is measured in inches.

F - Load Index. This indicates the maximum load capacity of the tyre. This is a numeric code and for each numeric code there is a specific weight which a tyre can carry.

G - Speed Symbol. This alphabet indicates the maximum speed a tyre can endure. Each alphabet code is assigned to certain speed limits.

I will talk more about Load Index and Speed Symbol below.

Load Index

A tyre’s load index classifies the maximum carrying capacity (in kg). Load ratings and speed ratings should be looked at together when you buy. Below is the chart that describes the load index and the corresponding load a tyre can carry.

(Chart 1)

(Chart 2)

The load index of a tyre is measured as the sum of kerb weight of the vehicle and the maximum movable weight of luggage and passengers that can be added in the vehicle. 

The kerb weight of a vehicle is the original mass of the vehicle along with the weight of weight all necessary liquids (fuel, engine oil, coolant, other cleaning liquids), repair kit, spare wheel and other necessary tools. Movable weight comprises of luggage that can be stored in the car and the sum of weight of each passenger that can travel in the car.

Example:

A. Kerb weight of a car = 1500 Kg

B. Weight of all movable luggage = 500 Kg

C. Max Capacity of passengers = 5

D. Weight of each passenger = 75 Kg (average)

E. Total weight of passengers = 375 Kg

The load index for tyres to carry a maximum weight of 2375 Kg (A+B+E) should be 102.

There are a lot of websites that you can use to calculate the load index of a tyre.

Speed Rating

Speed rating is the alphabet code that denominates that the highest speed a tyre can endure. I must say how important this aspect is. The speed rating defines the maximum speed at which a tyre can carry the specified load which is defined by the load index under specific conditions of usage which are defined by the manufacturer.

If your vehicle has tyres with 'F' speed rating, it essentially means you can go up to maximum speed of 80 kmph or 50 mph.

Occasionally you can drive at high speeds. But, do not make it a norm. The reason behind it is if you drive your vehicle at higher speeds with tyres that has comparatively lower speed rating, it may result in tyre bursts. Let me tell you this, an accident caused due to a tyre burst can be "fatal".

Below is the speed rating that you usually find your vehicle tyres:

(Chart - 1)

(Chart - 2)

Now, we have officially reached at the end of the blog.

This is all the information you will ever need to know before purchasing a tyre for your scooter, motorcycle or car.

Do stay tuned to this blog to know more information on tyres.