The equivalence between
old and new agricultural tyre markings

You will have noticed by now that there are a number of different markings on your tractor tyres: a dimensions marking that is common to all recent tyres, along with other markings that can be trickier to understand. In this article, we provide you with a helpful table to navigate these different codes so you can make sure you're choosing the right size tyre.

Markings are governed by a european standard to simplify and standardise tractor tyre dimensions

The ETRTO (European Tyre and Rim Technical Organisation) introduced the ISO 5775 standard to help clarify tyre dimensions, which used to be somewhat vague: sometimes in inches, sometimes in millimetres, and very often varying from one manufacturer to another.

The new ETRTO standard has brought a certain degree of standardisation to tractor tyre markings. However, it's entirely possible that your tyres are a little older, from an unknown brand, or are trailer tyres that do not yet meet this standard.

You therefore need to understand all of these other markings to be sure that you're buying the equivalent in the right size under the new standard.

Older tractor tyre markings are often given in inches, using the following format:

Here's what you need to know to understand the dimensions markings for older tyre models.

You will see a code that more or less matches what is shown in the photo opposite:

13.6 R 28
or 16.9 R 30
or 12.4 R 28
or 8.3 R 24
etc...

The first number is the width of the tyre in inches, so the tyre in the photo is 13.6 inches wide (flange width = the distance between the outside of the sidewalls in an inflated tyre).

The letter R stands for radial, a type of internal tyre structure (a dash instead of an R refers to a bias tyre).

The final number, 28 in the photo, is the rim diameter in inches (1 inch = 25.4 mm).

The european ETRTO tyre marking system provides greater clarity

If you're looking to replace your tyres, here's everything you need to know about the new European tyre marking.

It is made up of a series of letters and numbers in the following format:

600/65 R 28
or 460/85 R 38
or 750/55 R 26
etc...

The first number is the tyre width in millimetres, so the tyre in the photo is 600 mm wide (flange width = the distance between the outside of the sidewalls in an inflated tyre).

The second number is the sidewall height expressed as a percentage of the width, so the '65' in the photo means 65% of 600 mm = 390 mm sidewall height (this figure corresponds to series, such as 50 series, 60 series, 65 series, 80 series etc. The higher this number, the higher the sidewall).

The letter R stands for radial, an internal tyre structure.

The final number, 28 in the photo, is the rim diameter in inches (1 inch = 25.4 mm).

Here is the dimension equivalence table for old markings in inches (or trailer tyre markings) and the new marking standards for agricultural tyres

This table shows the equivalents for new and old markings, as well as the different tyre width options for the same rim (narrow wheels or wide tyres, depending on the type of work they're needed for).

95 - 90 - 85 - 80 series

75 - 70 - 65 series

60 - 55 - 50 - 45 - 40 series

To find out more about tyres or how to boost your farm's profits, download the free Bridgestone Agriculture eBook below:

The information contained in this publication is for guidance purpose only. Whilst every effort has been taken in its production, no responsibility can be accepted for any loss or damage arising from any kind of undetected technical or commercial error contained in this content. Any data supplied in this publication is subject to possible revision following the date of publication. Due to the constant advance of tyre technology, the contents of this publication are subject to change without notice.