Farm Ireland

Tuesday 12 December 2017

time for tyre testing

Bruce Lett

New technology can carry huge loads at low pressure

Regardless of how advanced a modern agricultural tractor may be or the technology used in its design and construction, almost all need tyres to transfer this power into work.

Many owners put no more thought into tyres than the fact they are black and, unless punctured, round.

Tyres, though, are a crucial element of any agricultural tractor, particularly those involved in tillage operations. Even though they are still black and round, tyre technology has come a long way.

A decade or two ago, there would rarely be a tillage tractor in sight without a set of dual wheels to carry the corn drill or harrow. The horsepower and size of the average tillage tractor have been steadily creeping up over the years, but it is far rarer to see a set of dual wheels on anything. Tyre technology has advanced to the point where tyres that are not overly large can carry huge loads at quite low pressures.

Many modern tyres have the ability to carry heavy loads without causing the level of compaction that will damage the structure of the soil beneath it and reduce crop yields. All strive to create a large footprint, so as to spread the tractor and implements' weight over a greater area.

A big footprint, combined with as low a tyre pressure as possible permitted by the tyre manufacture, reduces the negative effect on soil structure.

Tillage farmers and contractors tend to be more conscious of the various tyre options out there, primarily because of the impact of the use of heavy kit.

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There is more pressure on contractors to run on the correct tyres because their clients all tend to be farmers and want as little damage done as possible, whether it is a one-pass cereal establishment or slurry spreading. There is a wide range of tyre options open to tillage farmers and contractors these days. Lower-profile tyres, such as 65 and 60 series, are popular because they have a greater carrying capacity at lower tyre pressures.

The numbers 60 and 65 represent the tyre's aspect ratio; this is essentially the ratio of the tyre's height to its width expressed as a percentage.

There are many other profile options, with 85s being the older, normal standard. In many cases, 70s or 65s can be fitted on 85 series rims if changing worn tyres on an existing tractor.


This can get complicated, particularly on a four-wheel-drive tractor where it is important to match the front and rear tyres so as not to mess up the inter-axle ratio and cause some expensive damage to the axle or drive-train.

The inter-axle ratio tends to be somewhere around the 3pc mark, in that the front wheels are driven around 3pc faster than the rears when the tractor is in four-wheel-drive. This makes the tractor easier to steer in difficult conditions, pulling the tractor into line or the direction the wheels are being aimed.

Tyre retailers and tractor dealers can offer an awful lot of advice to anyone replacing tyres, in particular if you are hoping to change for lower-profile tyres on existing rims.

They will work out the correct tyre sizes to match inter-axle ratios as well, so don't get too bogged down in this detail. More important is the tyre's load-carrying capacity at various pressure levels.

Again, the lower the pressure and the higher the load the better. Don't forget this will be for one wheel only, so double the load-carrying capacity to get the tractor's total load carrying capacity. And, of course, do not lose sight of the price. Shop around for the best brands at the best quotes and make sure they are fitted prices.

Indo Farming