Tractor Tyre Guide

This guide aims to help you understand your tractor tyre's size, tread pattern, load carrying capacity and maximum speed.

Metric Tractor Tyre Sizes - 420/85R28, 460/70R26, 540/65R38

Most modern radial tractor tyres are marked up with metric sizes such as 420/85R28, 460/70R26, 540/65R38. The first number in the marking is the tyres width in millimetres. The last number is the rim diameter in inches (the hole in the centre of the tyre). The letter 'R' informs us its of Radial construction (not the older crossply construction). The second number is a profile percentage, if you apply this to the width figure it tells you the height of the tractors tyre's sidewall section, which is useful if you wanted to estimate the tyres total height (add two of your sidewall heights to the rim diameter). Getting the profile correct is important as it ensures that you maintain your tyres heights so that you don't disrupt the gearing ratios or transmission on four-wheel drive (4WD) tractors.

Imperial Tractor Tyre Sizes - 12.4-28, 16.9-30, 18.4-38

Most classic tractors use the older crossply type tractor tyres. Their size markings are written in imperial numbers such as 12.4-28, 16.9-30, 18.4-38. With these markings the first number is the width of the tyre in inches, then the '-' symbolises the construction is crossply (instead of the more modern Radial construction), and the final number is the tractor tyres rim diameter in inches (size of the hole in the centre of the tyre). With these older markings it is generally assumed that the profile percentage is 85%. That means if you want to find the modern Radial equivalent you would convert the width given in inches into millimetres, assume the 85% profile, and keep the rim diameter the same. So a 16.9-30 would become 420/85R30 for modern radial tractor tyres. Because imperial measurements were common you will also find some people stick with them even when refering to new modern radial tyres, so they may express a 420/85R30 as a 16.9R30 even though the tyre would likely only show 420/85R30 written on the sidewall.

Other Tractor Tyre Sizes - i.e. 26x12.00-12, 31X10.00-20

Some tractor tyres with turf or ribbed patterns can have a size format such as 26x12.00-12, 31X10.00-20. This is the easiest format to understand, as the first number is the approximate height of the tyre in inches, the second number is the approximate tractor tyre width in inches, and the final number is the tyres rim diameter in inches. The '-' symbol again tells us the tyre is of crossply construction.

Construction - Radial (R) vs Crossply (-)

Most new tractor tyres are now made using Radial tyre construction technology. Radial tractor tyres have many benefits over the older crossply versions, as they are designed to flex more and dissipate heat better. This means you get a wider and longer tread footprint, that slips less and provides more traction, so increases power transfer efficiency, reduces fuel consumption, gives a more comfortable ride, and which can be run at lower operating pressures. Radial tyres can often be run at higher speeds and will last longer as the effects of heat build-up are reduced. Older crossply tractor tyres are still used in slower moving machinery such as lawnmowers, forklifts and older classic tractors and buses. They are still used as they are often cheaper to produce and can also provide a firmer ride which is a benefit for some applications like on scissor lift platforms. In general, to ensure correct operation you are advised to keep with the same construction as you currently have, and to ensure you have the same construction on both sides of any axle.

Ply Rating / Load Rating / Speed Index

Modern radial tractor tyres will all have a series of 3 or 6 numbers on them which indicate how much weight the tyre is designed to carry at set speeds. You may see something like 153A8 or 163D. The table below can be used to look up what that first number means in Kilograms. The letters and numbers after that tell us the maximum speed that the tractor tyre is designed to run at, and again the table below show you what the varying letters mean. Older tyres don't have these markings but may have a Ply Rating on the tyre. The ply rating is a reference to tyres carrying capacity, and you should look for the same ply rating when replacing your tractor tyres. It is sometimes abreviated to just P.R. on the tyre side wall. 

Converting Imperial to Metric - i.e. 16.9-38 = 420/85R38, 480/70R38, 540/65R38

Use the table below to quickly convert your older imperial crossply markings into their newer metric radial marking. With the older imperial markings it is generally assumed that the profile percentage is 85%, so use that if you want to keep the tractor tyres width and height the same as the current crossply size (ie.16.9-38 = 420/85R38).. If however you want to go to a wider (or narrower) tread for more traction or flotation then you can also use the table below to convert your 16.9-38 into the wider but lower profile options of 480/70R38, 540/65R38, 600/60R38. These alternate width/profile options work to ensure your tyres overall height remains constant (within tolerances) to ensure your tractors gearing ratios or transmission won't be affected by the change if you have a 4WD machine. Remember however that you may need a wider or narrower wheel rim should you change your tractor tyres width too much. 

Tractor Tread Patterns

Most manufacturers of tractor tyres ensure their tread designs fall into one of the below main categories;

R1

R2

R3

R4

F2

F3

I-1

Traction Implement

Flotation Implement

Flotation Transport

R1 - Most tractor tyre treads have the R1 traditional chevron cleated open centre design. It is also referred to as a tractive tractor pattern. It is ideal for traction in field work.

R2 - The R2 pattern has a very deep tread and is designed for extremely wet or sticky soil. It is also known as "Rice & Cane", "Paddle" or "Spade" tyre pattern.

R3 - This is the non-marking grassland turf pattern often made of diamond shaped block lugs that are shallow and non-aggressive so as not to leave a mark on the ground. Perfect for tractors operating on golf courses and other grounds maintenance machinery.

R4 - The R4 pattern is also known as an industrial wide lug or ATU (all Traction Utility) tread. The lug design is an 'L' or 'hockey stick' shape that overlaps slightly in the middle of tread. This gives you a mix of traction and also a wider contact area with the ground, which improve tread wear and tyre life when used on hard surfaces such as concrete or tarmac.

F2 - Tractor front tyres commonly with a 3-rib pattern, but also available in 4 or 5 rib version, that are used on the front axle of two-wheel-drive tractors and on some agricultural implements. These tyres are often available with notches or lugs in the outer ribs to improve grip and self-cleaning.

F3 - an Industrial tractor front pattern that is flatter than traditional F2 rib tractor tyres and so are optimised for road and hard-surface performance. They may sometimes have shoulder lugs or zig-zag ribs and can often be similar to I-1 Implement tyres.

I-1 - The I-1 pattern is also referred to as a "Multi-Rib" tyre. They are used on a huge range of farm implements and trailers. They offer high flotation and load capacity at lower pressures and make for a good all-round tyre.

Traction Implement - Like an R1 or R4 tractor tyre pattern but designed for use on the drive wheels of agricultural and industrial implements.

Flotation Implement - Like an R4 pattern but typically built to minimise soil disturbance and to carry high loads at low pressures. They are used on a range of farm trailers and implements.

Flotation Transport - Designed for stability and road performance without sacrificing flotation and grip in the field. They are often suitable for higher speeds than other farm trailer tractor tyres.