There are multiple sizes and varieties of car tires based on the vehicle’s type, usage, reign’s temperature, and weather conditions, either wet or dry. Tires of different dimensions are made for different land types, e.g., wider-based tires for sandy roads and narrow-based for concrete established roads.

Wider tires are used for vehicles with heavy loads or high-speed racing cars because wider tires have short braking distances and better handling. More than one size tire may be compatible with your vehicle, but it would be better to choose the factory’s size for your vehicle.

Different tire types have different lifetimes; therefore, you should change them to avoid any accident after a given time. Life span also depends on the meterage of the car. Some cars travel more average distance than others have travelled. For maximum lifespan, we should choose the right size that would be compatible with your vehicle.

I will discuss some important features and facts about the car’s size in a simple but effective way to help you choose the right thing.

Cross Section Width

The measurement of a tire from inner sidewall to outer sidewall is called its cross-section width or tire width. For example, P215/65R 15 95H is the total size of a tire, but the number 215 after the letter P is the tire’s width measured in millimeters.  Protective ribs, decorations, and raised letters are excluded when we measured the tire section width. In Europe, to measure a tire’s width metric system is used, and this measure takes in millimeters. Cross-section width is measured before putting any load on the tire, which gives the correct measurement.

Before measurement of a tire is mounted to its rim, which the factory gives.

The tire’s cross-section width is different according to the tire’s rim; therefore, use the rim given by the factory always. The different rim size can damage the tire severely and deformed the tire shape.

Aspect Ratio:w

The percentage between the height of the sidewalls and width is called the aspect ratio.

For example, P215/65R 15 95H is the size of a tire; the number after the slash is 65, called the tire’s aspect ratio. We take the aspect ratio in percentage; it means the tire’s sidewall height is 65%. If the aspect ratio is lower, the height of the sidewall will also be lower. If the tire’s aspect ratio is 55% or lower, it is called a low profiled tire. There are some pros and cons of the low profiled tire as given below.

Pros

Cons

Warning​:

Never use the mix of regular-profile tires and low-profile tires on the same car because this can cause a dangerous road accident.

Construction Of A Tire

There are two types of tires based on construction. For instance, 205/55 R 16 94H XL and 205/55 B 16 94H XL shows

1)  Radial Tires

2) Bias-ply Tires 

Firstly, radial tires are internal construction of tires based on plies of cord, and the network of threads is referred to as a carcass. These threads are made up of polyester, steel or other types of textile materials. These cords are perpendicular to each other from the travelling direction.

More than 95% of passenger cars have radial ply tires because they have less rolling friction, better steering control, more grip on brakes, better fuel economy and longer tread life.

Secondly, belted or bias-ply tyres are mostly used in trailer tires and for rough roads. The belted ply construction is crisscross, and threads are overlapped with each other to provide a smooth ride on bumpy roads.

These tires have rigid and stiff sidewalls to carry heavy loads.

Wheel Diameter

Before knowing the wheel diameter, you should think about the components of a wheel. A wheel has two main parts: A tire and a rim, which are required to measure the tire’s diameter. You will measure the wheel’s diameter collectively. For instance, P 255/55 R 18 97T, the number after construction shows the wheel’s diameter in inches as “18.” which is shown in the example. In the wheel’s diameter, the tire’s sidewall length and rim’s diameter are included.

Load Index

The load index tells you how much maximum load you can carry. For instance, P 255/55 R 18 97T is the total size of a tire after wheel diameter; 97 is referred to as a load index, equivalent to 730kg, a maximum load you can carry.

Load Index

95

96

97

98

99

Load in KG

690

710

730

750

775

Speed Rating

The speed rating chart shows the maximum safe speed at which you can drive. The letter after the load index shows the speed rating; it varies from A to Y.  in the example,” P225/70 R 16 91S,” the last letter “S.” shows the speed rating equivalent to 180 km/hour. Speed ratings such as A1, A2 ….. A8 have low-speed tires; on the other hand, V, W, and Y show high-speed rating tires. You can easily choose tires for your car by following the speed rating chart.

Speed Symbol

A1

A2

A3

A4

A5

P

Q

R

S

T

Speed in (km/h)

5

10

15

20

25

150

160

170

180

190

Speed in (mile/h)

3

6

9

12

19

94

100

106

112

118

FAQs

Can I use different size tires on my car?

It is possible to change the size of your tire without changing the diameter of the wheel.

Can I use tire having the cross section width 235 instead of 225?

Yes, you can use tire of width 235 instead of 225, because width do not affect the diameter.

From where can I find tire size?

Following are the places from where you can find your tire size.

1) On your tire’s sidewall, you can find it easily.

2) You can find it on the driver’s side door jamb.

3) In the car inside the glove box door, you also can find.

4) You can find it within your gas tank hatch.

5) You can find it in your owner’s manual.