Tyres play an important part in the driving experience and safety of a vehicle. However, installing the correct tyres on your vehicle can be a confusing task. Your choice of tyre should reflect the conditions under which you drive and your preferences for vehicle response and handling. Reading the sidewall of your existing tyre can help in ordering the right tyres. In this article, we will look at how to read tyres looking at the sidewall of an automotive tyre.

Vehicle categories “P” AND “LT”

A Toyo passenger car tyre

You will see the letter “P” on most of the vehicles. The “P” stands for “P-metric” which is a Tyre and Rim Association designation for “passenger car” tyres. These tyres are made for passenger vehicles. Suitable vehicles include- hatchbacks, sedans, SUVs, and light-duty pickup trucks. If you find LT at the starting of the sequence, it means “LT-Metric” which stands for “light truck”.  heavy-duty vehicles and trailers use light-truck tyres.

Tyre sidewall: Width

The first number that appears in the tyre information sequence is the tyre width. This is shown in millimeters, this will help you select the right tyre for your car: 225/70/R16 91S.

The width of the tyre represents the measurement from sidewall to sidewall. Therefore, a tyre with the dimensional detail “P225” is designed for a passenger car and has a width of 225 millimeters.

Tyre sidewall: Aspect ratio

The aspect ratio of your tyre comes after the width of the tyre. The aspect ratio refers to how tall your tyre’s profile is: 225/70/R16 91S. 

Aspect ratios come in percentages. Tyre manufacturers calculate the proportions by dividing the height of a tyre on the edge of its width. If a tyre has an aspect ratio of 70, it means that the height of the tyre is 70% of its width.

Construction

The radial and diagonal (bias) tyre construction

After the aspect ratio, next comes the internal construction maintaining your tyre’s stability: 225/70/R16 91S.

Two kinds of constructions can be seen on your tyre: R(radial) and D(Diagonal or Bias Ply)

The radial tyres have the cables in the interior constructed and oriented in a radial direction, from one dot to another, generally perpendicular to the axis of the revolution.

Tyre sidewall: Rim diameter

The next number in the sequence is the diameter code. This number comes in inches. This number shows the size of the rim on which suits the tyre. For example, a tyre with the 225/70/R16 91S would fit a rim with a diameter of 16 inches.

Load index & Speed rating

The load index and speed rating on tyres

After the rim diameter come the tyres load index, which tells the maximum weight the tyre can support when completely inflated, this value is calculated in kilograms: 225/70/R16 91S

The load “index” number does not tell the precise number of kilograms the tyre can bear. However, the number corresponds to a particular load capacity in an index. Beginning with 60 and ending with 179, the load index digits indicate load capacities from 250 to 7,750 kilograms.

The last figure in the tyre size sequence is the speed rating. This is shown by a letter: 225/70/R16 91S. The speed rating letter compares to an appropriate speed capability based on a standardized lab test.

A tyre rated with “S” can go up to 180 km/h, while a tyre rated “R” can speed up to 170 km/h. 

In fact, tyres with higher speed ratings, often offer increased handling and performance. 

Always make sure the Replacement tyres have similar or higher speed ratings to maintain vehicle speed capability. Moreover, if different tyres of the vehicles come with a different speed rating, the vehicle will perform at the rate of the lowest tyre.

Also, read:

Wheel alignment and balancing: all you need to know

Sustainable tyres: a step towards a sustainable future?