Proper sized tires deliver powerto the ground

Undersized, overinflated tires will limit power, 
waste fuel and cause soil compaction

Now is a good time to do an inventory of farm implement tires to determine what needs to be replaced before the snow melts.

There are a number of considerations, such as making sure tires aren’t undersized, says James Crouch, manager of agricultural tires for Michelin.

“Who ever heard of such a thing? You’ve probably never even thought about a farmer having tires that are too small on his tractor, but here’s how it happens,” said Crouch, who used the example of a farmer with a 9630 John Deere that he modified, or “chipped,” over the winter to increase its power.

“So instead of 530 horsepower, now the guy has 620 or 650 h.p. His horsepower has dramatically increased. He had been running dual 620/70/42s before, but now he gets power hop, and slippage is dramatically higher. Actually, we see this often.

“His old tires might be in perfect condition, but they don’t match the new power. He’s putting too much torque to the ground. He’s undersized on his tires, so now he has to move up to something like a 710/70/42 or an IF (increased flexion) tire.”

Crouch said a tire’s job is to transmit power from the engine to the ground. If the tire isn’t doing its job, the farmer is wasting fuel and even more importantly, wasting part of his investment in the equipment.

“On the new John Deere 9620R, the standard dual tire is an 800/70R 38. Now that’s a really big tire, but that’s what they need to put that power to the ground,” he said.

“They used to run a 710/70 42, which is the same height but it was a narrower tread. And before that it was a 620/70 42. The footprint grows progressively larger as the power increases.”

No method is available to quantify the damage that stubble can do to a tire, but every farmer with experience in B.t. corn knows that a tire can be severely damaged or ruined by stubble.

To combat this problem, manufacturers of agricultural tires are continually tweaking rubber compounds to make their tires stand up better to tough standing stubble. It’s possible to formulate a compound that’s impervious to stubble damage, but those tires would probably ride like the old iron wheels on the first tractors.

Crouch said Michelin has introduced a VF row crop tire that carries a two-year free replacement guarantee against stubble damage called the Stubble Shield.

“We’ve tested that tire for the past few years in no-till B.t. corn just to make sure it stands up,” he said.

“We think we have the right combination of rubber compound and tread angle. One of the things we discovered is that a steeper pitch on the tread is better in stubble because it deflects the stubble toward the shoulder. A flatter tread is more prone to stubble damage.”

Crouch said soil compaction is a major focus at Michelin’s research and development department. There’s only so much an individual farmer can do to fight compaction unless he has help from the tire companies.

“Just like the farmer, we want to bring soil compaction down to a minimum,” he said.

“Our tire technology has helped a lot so far. Our UltraFlex technology allows our tires to get really, really low in pressure and still hold up. We have the IF designation, which is increased flexion, and VF, which is very high flexion.

“When we sell you a brand new set of tires, once they’re mounted and installed on your tractor, a Michelin rep will come out to your farm and weigh your tractor on a set of DOT scales so he can give you a pressure recommendation. But you’re limited because you have to set your tractor tire pressures for the worst case scenario.

“The worst day in the life of those tires is when you’re pulling your planter down the highway from one field to the next. So the rep hooks up your planter folded into transport. And your tire pressure recommendation will be based on that scenario, maybe something around 26.”

Crouch said the recommendation will be high for field use. It’s good for tire life and from a safety point of view, but it will cause major compaction problems in the field.

The tires shouldn’t have that much pressure when pulling a drill or a planter, he added.

“In the field, those tires might be best down around 13 (pounds per sq. inch). Now your soil compaction is way less. Your traction is way better. Ride quality is better.”

“Central inflation lets you lower the pressure while you’re in the field working and raise the pressure up to the recommended level for transport.

“Central inflation is a fantastic tool in letting you manage your tires better and basically manage your soil better,” said Crouch.

“We’re working closely with European and domestic manufacturers to make sure our ag tires are suited for central inflation systems. Farmers and industry all have the same goal. We all want to get tire inflation as low as possible so we can keep soil compaction to an absolute minimum.”

Crouch said some Michelin tires for big four-wheel-drive tractors are now rated as low as six p.s.i., but only in certain conditions.

Adhering to the recommended pressure for different conditions will also promote longer tread and casing life, he added.

KalTire recently organized educational seminars about soil compaction in Manitoba, said Greg Smelski, the company’s zone manager in Brandon.

“What we found was that some of the older generation farmers didn’t have any idea how compaction can cut into their yield,” he said.

“With the new tractors and the newest radial tires running at ex-tremely low pressures, everyone’s getting away from the calcium ballast and going to the dry weights.

“If you’re putting calcium into a radial, you’re essentially changing that expensive radial tire into a bias ply tire. The walls of the radial can’t flex the way they’re supposed to. You want the ballast on the tractor itself so you get the right balance. You’re hurting yourself by putting ballast in the tires.”

Smelski said KalTire does not offer central inflation, but it is working to develop a pressure monitoring system for agricultural tires.

The system will have a sensor and transmitter in each tire that send continuous p.s.i. readings to a display in the cab. It’s not as convenient as central inflation, but it will alert the operator to any extreme under or over inflation.

“With duals and triples, the valves are hard to get at. And if you have over-inflated tires, you’ll get slippage, and that wastes a lot of fuel,” Smelski said.

“The other concern with duals or triples is you have to run the same pressure in all the tires. There’s no point in running multiple tires if only one of the tires is carrying all the load and doing all the work. That’s where a pressure monitoring system or central inflation pays for itself.”

Equipment on bigger farms must put on a lot more road miles getting from one end of the farm to the other, which Smelski said is another argument for a pressure monitoring or central inflation system.

“Some of the European tractors are capable of 60 m.p.h. Most of our domestic tractors can run down the road at 30 m.p.h. If you’re travelling those speeds with tire pressures down at 12 p.s.i., that’s dangerous,” he said.

“The other aspect is that equipment manufacturers are becoming a lot more demanding about what tires can go on the machines they sell us. They have very strict specifications about size, highway speed and weight capacity.”

Smelski said farmers might find replacement tires that are the same size, but they may be setting themselves up for a bad crash and a major legal liability if the speed and weight specifications aren’t correct.

Bargain basement priced tires may work in less demanding situations on older implements, Smelski said, but he wouldn’t put them on a newer tractor, sprayer, grain cart or combine. Those lower priced tires are usually bias ply, and Smelski said bias ply tires will eventually disappear from the market.

Michelin has a new lineup of high quality seamless farm tire tubes made of 100 percent butyl rubber for farmers who still want to run calcium ballast.

The new inner tube is designed to reduce the risk of the corrosive liquid leaking out and corroding the wheel. The tubes are available in multiple sizes to fit Michelin and competitor brands.

For more information, contact Smelski at 204-573-7866 or visit

About the author



Stories from our other publications