How to Read Tyre Sizes, Labels and Speed Ratings

Trying to decode a tyre’s sidewall without any prior knowledge is enough to leave your head in a spin. The reality, however, is that it’s pretty simple.

From load indexes to speed ratings, constructions to aspect ratios, there’s a whole host of tyre terminology that combines to create a picture of the capabilities and compatibility of a tyre.

To help you get to grips with tyre markings, we’ve created this nifty guide. Want to quickly find out the physical measurements of your tyre? Check out our ‘Find Your Tyres’ tool.

 

Are tyre markings important?

When it comes to staying safe on the road, tyres are among the most important components of your vehicle. Whether you’re steering, braking or drifting along, they are at the epicentre of the action. After all, this is the only part of your vehicle which actually touches the ground. Thus, when it comes to tyre replacements, it’s crucial you get it right.

Enter, tyre markings. These are used to identify the specifications and physical features of a tyre, so you can find a replacement which works in tandem with your vehicle. While a few of these tyre markings are of little importance, most of them have a significant effect on performance and safety – so it’s important to get right.

“While tyres might look like they are just rings of rubber, each one is unique. Therefore, it’s crucial that you double-check your tyre markings before confirming any booking. Not doing so could result in you purchasing tyres that are incompatible with your vehicle and, thus, can’t be fitted. When in doubt, always get in touch with our friendly advisers for help and advice.”

Daniel Bezer, Tyre Expert

Where to find tyre markings

It will probably come as no surprise that tyre labels are etched into a tyre’s sidewall (i.e. the external side facing you). But what you might not know is that you can find information relating to your manufacturer-recommended tyres in a few other places too, including:

  • The vehicle owner’s manual
  • Fuel cap hatch
  • Inside your glove box door
  • The driver’s doorjamb

 

It’s worth bearing in mind that your tyre’s sidewall only represents the specifications for that particular tyre. To be sure that a tyre is compatible with your vehicle, you should consult your owner’s manual or one of the above places.

When in doubt, you can also get in touch with the Tyres on the Drive team.

 

How to read your tyre’s sidewall markings

A tyre sidewall contains a lot of information. So, let’s start by focussing on the short sequence of letters and numbers which represent the size code.

We’ll use the example: 225/55 R 18 95 H

Sidewall markings


  1. Tyre width
  2. Aspect ratio or profile
  3. Tyre construction
  4. Rim diameter in inches
  5. Load index
  6. Speed rating index

1. Tyre width


The next number in the sequence is “225.” This represents the tyre’s width in millimetres – measured from sidewall to sidewall.

2. Aspect ratio or profile


The following two numbers (“55”) represent the aspect ratio – or measurement of the sidewall height (in mm). Essentially, this is the ratio of the tyre’s cross-section to its width. So, in the above example, a tyre that has an aspect ratio of 55 would have a height equal to 55 per cent of its width.

3. Tyre construction


Next up is a letter. This tells you how a tyre is constructed. In this example, the “R” means that the tyre has radial construction. This is where the internal ply cords extend across the casing from bead to bead, in a radial direction. 

Less common tyre constructions include diagonal or bias ply, represented by the letter “D”.

4. Rim diameter in inches


The next number represents the diameter code. Unlike the width, this is shown in inches. This is particularly important because it represents the diameter of the wheel rim. In the above example, the number “18” means that the tyre should be matched to a rim wheel of 18 inches.

5. Load index


After the rim diameter, we find the load rating. This tells you the maximum capacity of a passenger car tyre when it is inflated to its maximum safe pressure. The figure (in this example, “95”) refers to the index rather than the weight. As such, you will need to consult a load index table (below) which determines the load in kg for each rating. For a load index of “95”, the maximum load weight is 690kg/tyre.

Load index Load in kg Load index Load in kg Load index Load in kg
 62  265  84  500  106  950
 63  272   85  515  107  975
 64  280  86  530  108  1000
 65  290  87  545  109  1030
 66  300  88  560  110  1060
 67  307  89  580  111  1090
 68  315   90  600  112  1120
 69  325  91  615  113  1150
 70  335  92  630  114  1180 
 71  345  93  650  115  1215
 72  355  94  670  116  1250
 73  365  95  690  117  1285
 74  375  96  710  118   1320
 75  387   97  730  119  1360
 76  400  98  750  120  1400
 77  412  99   775  121  1450
 78  425  100  800  122  1500
 79  437  101  825  123  1550
 80  450  102   850  124  1600
 81  462  103  875  125  1650
 82  475   104  900   126  1700
 83  487  105  925    

6. Speed rating index


The final tyre marking in this string represents the speed rating. As you might have guessed, this denotes the maximum speed a tyre can sustain when it is correctly inflated and under load. As with the load index, this letter references a look-up table which indicates the maximum permissible speed of a tyre. In this example, “H” means the vehicle has a maximum speed of 130mph under the maximum load.

Speed rating Mile /hour Kilometers /hour Speed rating Mile /hour Kilometers /hour
 N  87  140  U  124  200
 P  93  150  H  130  210
 Q  99  160  V  149   240
 R  106  170  Z  150+  240+ 
 S  112  180   W  168  270
 T  118  190  Y  186  300

“Although a speed rating table references the maximum speed a tyre can move under load, you should not use this as a threshold. Always drive at the speed limit and do not put your tyres under any undue stress.”

Daniel Bezer, Tyre Expert

Additional tyre markings

Aside from the above tyre size sequence, you may see a handful of other tyre markings. These could include:

 

  • Tyre manufacturer
  • Model name of tyre
  • Country of manufacture
  • TWI (Tread Wear Indicators)
  • DOT (Department of Transportation)
    • This string of letters and numbers indicate the production and factory date. The last four numbers make up the date section of the code e.g. 4419 would represent the 44th week of 2019.
  • ECE approval mark and number
    • This indicates that the tyre has been tested and passed European safety standards.
  • Maximum tyre pressure (in both bar and psi)
  • Letters ‘P’ and ‘LT’
    • In some instances, a tyre number sequence will start with the letter “P”. This stands for “P-metric” or “passenger.” This is the most common type of tyre and is designed to be used on passenger vehicles. LT stands for light truck and is designed for SUVs, vans, and the like.
  • Maximum load (in kg and lbs)
  • M+S.
    • This indicates that the tyre is suitable for mud and snow.
  • 3PMSF (Three Peak Mountain Snow Flake)
    • This marking shows that a tyre can perform at temperatures below zero. Winter tyres and all-season tyres are more effective at handling in the cold, and are suitable for difficult weather conditions.
  • Tyre direction
    • The word “rotation” or “direction” will precede an arrow which indicates the tyre’s forward direction.
 

What happens if I fit tyres with a different speed or load index?

Fitting tyres with different speed or load ratings can cause big problems if you don’t understand what these are and what your vehicle is equipped with. Let’s start with what each of these values represents:

Speed Rating

The speed rating on a tyre converts to a maximum speed that the tyre is manufactured to travel at, in conjunction with a specified weight. This rating determines how well the tyre copes with cornering, acceleration and braking.

Load Rating

The load rating on a tyre converts to a maximum weight that each tyre is manufactured to support at a specified speed. The UK law requires the load rating to be equal to or higher than the tyre that is recommended by the vehicle manufacturer for the tyre size that is fitted.

“The only exception to fitting a lower speed rating to a vehicle is when you come to fit winter tyres to your vehicle – as long as you don’t exceed the tyres maximum speed limit.”

Daniel Bezer, Tyre Expert

Still unsure which tyres are suitable for your vehicle? Find the right tyres by typing in your registration details, or get in touch with our customer support team by calling 0333 016 6550.

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