How to maintain optimal air pressure on tractor tires

Soil compaction can rob soil of its ability to hold water and air, leading to yield losses. Combat this by working with the proper tires on your tractor, knowing the weight carrying capacity and speed requirements, and how to adjust that for a variety of working conditions.

Tire load speed index

Both the weight carrying capacity and speed requirements must be assessed to choose the proper load speed index.

"When determining speed requirements, I recommend determining both in-field and transport maximums," says David Graden, global account manager for Michelin Agriculture. "Knowing physics enables a standard tire to carry load with significantly less air pressure at slower speeds — this is very important if you are concerned with reducing soil compaction."

On the sidewall of a tire, you can find the load speed index expressed like this, for example: 173D.

Most manufacturers will issue reference materials for inflation tables, with standardized tables available as well. Broken down, the first three numbers are the load indices, or weight, a tire can carry. The letter, noted by "A8," "B," or "D," indicates the speed rating of the tire.

The speed rating for each value is:

• A8 = 25 mph
• B = 30 mph
• D = 40 mph

"It is always important to make sure to match the maximum speed of the tire to the maximum speed rating of the tractor," says Bradley J. Harris, manager of global agricultural field engineering for Firestone Ag.

In North America, the B speed rated tires will be acceptable for most tractors. Currently, there are only a few tractors in the market that exceed 30 mph, but for those tractors, the D speed rated tires or higher are needed.

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For example, take a look at the Michelin 800/70R38 MachXBib tire with a load speed index of 173D. The tire can carry a max load of 14,330 pounds at 23 psi at 40 mph transport speed, and can carry the same weight at 6 mph in-field speed with 15 psi. Reducing pressure 8 psi over 5,000 acres can equate to a significant improvement in a grower's bottom line, says Graden.

To achieve this change in tire pressure on the fly, Graden recommends investing in a Central Tire Inflation System (CTIS).

CTIS to maximize yield

Load and speed indexes are vital information. If you buy a tire with too low of a load/speed index to cover your needs, you can overload the tire.

"That can lead to premature wear, accidents and spills, or even injury or death" says Blaine Cox, national product manager at Yokohama Off-Highway Tires America. "I can't say this too many times: you need to match the load and speed index of your tires to the machinery they will be running on."

Linking a compressor to each tire on the machine for on-the-go pressure adjustments, CTIS technology allows you to increase inflation pressure to run safely on the road, and decrease it for better performance and lower soil compaction in the field.

VF tire technology

The "Increased Flexion" technology, or IF and VF technology, has revolutionized how the traditional tire is employed through new rubbers and carcass (rubber and nylon casing construction) materials, according to Greg W. Gilland, business development ag segment manager for Maxam Tire International. IF and VF tires are able to carry additional weight at higher speeds, or reduce soil compaction through decreased air pressure, increasing the tire footprint for a given load.

• IF Technology Tires allows either 20% more tire load at normal pressure, or 20% less air pressure for the same tire load.
• VF Technology Tires allows either 40% more tire load at normal pressure, or 40% less air pressure for the same tire load.

The advantage of IF and VF Technology is the capability to reduce soil compaction with lower air pressure by extending the tire footprint, or conversely the ability to carry more weight at the same ground pressure or standard air pressure.

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Editor's Note: This content originally appeared in AG Tire Talk to provide answers that farm equipment dealers have about farm tire technology. This series features a trending question followed by an abridged version of the answers. For the complete answers, check out agtiretalk.com.