How to Read your Tyre Size?

Why tyre marking is important ?

Steering, acceleration, braking, traction, handling, comfort – the tyre is where it all happens. Tyres are a critical component of driving safety. During an emergency, your brakes stop the wheels from spinning, but it’s the tyre’s grip that truly brings your vehicle to a halt. Furthermore, tyre size, tyre load index, tyre speed ratings, and tyre pressure are crucial factors that have a significant effect on your vehicle's performance, fuel efficiency, and your vehicle's ability to cope with adverse weather and road conditions. Hence, it is necessary to understand this tyre information. It can be easily seen imprinted on the sidewall of your tyre and is called tyre markings. To help you further, here’s a quick guide to knowing the tyre markings and reading your car’s tyre size.

What are tyre markings?

Tyres on your car are like the shoes on your feet. Imagine buying shoes without knowing your right size. Likewise it’s important to know your exact tyre size when buying new tyres. The markings imprinted on your tyre represent tyre size and other important information about the tyre. Tyre markings indicate the width of the tyre, its aspect ratio, construction, speed rating, load index and more. Combined together these tyre markings or terminologies explain the overall capabilities of the tyre. Understanding the tyre markings helps you identify the important features and specifications of a tyre, which is crucial during tyre replacement. While buying new tyres if you do not get the tyre specifications right you will end up purchasing a set that is incompatible with your vehicle. This not only harms the vehicle’s performance but also the safety.

Where can you find the tyre size?

The easiest place to look for tyre size is on the sidewall of the tyres that fitted to your car. However, it’s better to double check the tyre size with information located at other places too. You can also find your tyre size at few other places like:

• Glove box
• Vehicle manual
• Inside the fuel tank cap
• Placard present on the driver’s door panel

The tyre size information that you find at the above places is the vehicle manufacturer recommended tyre size in order to provide safety, optimum performance, and fuel efficiency. Since each vehicle is different, weighs different, carries the load differently, always choose your tyre size in compliance with the vehicle, tyre manufacturer recommendations. And based on your requirement and driving needs like on-road/off-road ; sand/rocks/mud; race circuit track/normal street drive, choose the right tyres.  Whenever in doubt seek advice from a tyre specialist.

How to read your tyre size?

There are 2 types of tyre size measurement- metric and flotation. Size is usually expressed in the metric form and it is indicated on the side of the tyres with a series of digits and numbers. To understand better let us consider the metric type tyre size as an example - 205/55 R16 91 V

1. Tyre Width or Section Width

First is the section width or the width of the tyre measured from sidewall to sidewall in millimeters. The 205 means the width is 205 mm or 8.07 inches.

2. Aspect Ratio

Following the tyre width after the slash is the aspect ratio also known as the tyre profile. It represents the height of the sidewall compared to the section width and is expressed as a percentage. The 55 in our example means the sidewall is 55% of the width i.e. 4 inches.

Example: Tyre profile of 225/55 R16 is higher than tyre profile of 205/55 R16

3. Tyre Construction

Next, you see is the letter R which stands for Radial. There are two types of tyre constructions:

Radial – Denoted by R

Bias – Denoted by dash (-)

The radial tyres are largely used in all the modern vehicles that we see today. In this construction, the ply cords stretch from one bead to another in the radial direction at an angle of 90 degrees to the axis of rotation. This radial orientation of the cords offers improved safety and comfort while driving. Therefore, they are used in a majority of passenger cars and sports cars.

4. Rim Diameter or Wheel Diameter

The next figure indicates the wheel size. It is the diameter of the rim expressed in inches. In our example, it is 16 inches, which means this tyre will fit on 16 inches rims.

5. Load Index

The figure 94 in our example is what we call as load index or load capacity. That is the maximum amount of weight this tyre can carry at a maximum inflation pressure while the tyres runs at a certain speed, for a certain period of time.  You can look at the table below to decipher the figure 91. As seen in the table, 91 load index corresponds to 1356 lbs , which means the tyre can carry 1356 lbs or 615 Kgs. So, if you have four of these tyres then the whole set of four tyres can carry 5424 lbs (1356 X 4).

Now, for instance, consider:

• your car weighs 3000 lbs
• carries 5 average adults together weighing approximately 1000 lbs
• the weight of the extra items in the trunk is about 500 lbs

Hence, here the gross vehicle weight is 4500 lbs ( car weight + passengers’ weight + extra items’ weight).

In this case, the total weight that all four tyres of the vehicle can together carry has to be at least equal to or higher than 4500 lbs. Therefore, the tyre load index is always rated above your gross vehicle weight rating to give you a little bit of safety leeway. At all times it has to be equal to or higher than that specified by the vehicle manufacturer but never low. A tyre with a lower load index than the one recommended for the vehicle will not be able to carry the vehicle weight.

So when you go for a tyre replacement always make sure you perfectly match the load index of the new tyre with the recommended one.

Load Index	lbs	kg	Load Index	lbs	kg
71	761	345	91	1356	615
72	783	355	92	1389	630
73	805	365	93	1433	650
74	827	375	94	1477	670
75	853	387	95	1521	690
76	882	400	96	1565	710
77	908	412	97	1609	730
78	937	425	98	1653	750
79	936	437	99	1709	775
80	992	450	100	1764	800
81	1019	462	101	1819	825
82	1047	475	102	1874	850
83	1074	487	103	1929	975
84	1102	500	104	1984	900
85	1135	515	105	2039	925
86	1168	530	106	2094	950
87	1201	545	107	2149	975
88	1235	560	108	2205	1000
89	1279	580	109	2271	1030
90	1323	600	110	2337	1060

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6. Speed Rating

Speed rating is expressed as an alphabet. Each letter represents a maximum sustained speed. It basically describes how much centrifugal force a tyre can endure. In our example, V corresponds to 149 mph. The speed rating index can go as high as a Y rating. It is seen that the tyres with high speed rating are not only preferred by motorists who enjoy speed but also by the ones who do not drive that fast. The reason is it’s not just the speed rating but it’s also the performance rating and has to do with the cornering, handling, stopping and the maneuverability of your vehicle.

So, if your manufacturer calls for a V in the manual, make sure you go for a V speed rating. Just as in the case of the load index, for the speed rating you can go higher but never lower.

Vide	Maximum Speed
L	75 mph	120 km/h
M	81 mph	130 km/h
N	87 mph	140 km/h
Q	99 mph	160 km/h
R	106 mph	170 km/h
S	112 mph	180 km/h
T	118 mph	190 km/h
U	124 mph	200 km/h
H	130 mph	210 km/h
V	149 mph	240 km/h
Z	149+ mph	240+ km/h
W	168 mph	270 km/h
Y	186 mph	300 km/h
(Y)	186+ mph	300+ km/h

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Besides the tyre size series, there are a couple of other markings you might find on the tyre. Few of these include

• tyre brand name
• model name
• tread wear indicator
• traction grades
• temperature
• tyre pressure
• manufacturing date
• country of manufacture
• Some technologies like zero pressure, selfseal, acoustic etc.

These are the common tyre markings that will help you know your tyres. And, if you are still unsure which tyre suits your vehicle stop into one of the nearest TYREPLUS centers for a consultation from the tyre experts.