The Proof is in the Tire Tracks

NTS Tire Supply recently teamed up with Yokohama Off-Highway Tires and independent research company AgRevival to give you an up-close look at the impact tire pressure has on your farm. Our plan was simple: 

1. Outfit AgRevival’s sprayer with Alliance Agriflex VF tires.
2. Drive across our test plot at high (35 psi) and low (17 psi) tire pressures
3. Conduct rut depth, water infiltration, and soil compaction tests.  
4. Show farmers the difference in soil damage between the two tire pressures. (That was our plan, at least. As it turns out, our plan panned out.) 

For this study, NTS outfitted the sprayer, a 1,000-gallon Hagie 2101, with VF380/85R30 Agriflex+ 354 radial tires. (Yokohama Off-Highway Tires generously provided financial assistance for the tire upgrade.)

The One time When Shallow Thinking is Positive 

You already know that a self-propelled sprayer can be a beast to handle and a bear for your bottom line. You fight to stay between the rows. You endure a bad ride hour after hour. You burn fuel bulldozing through the dirt acre after acre. And you cause harmful levels of soil compaction with every pass that can squash your yields year after year.

‍Read More: Tire Footprint is the Key to Fixing Sprayer Performance Problems

When it comes to driving machines across your dirt, you want to make shallow tire tracks—not deep ruts. Rut depth is one physical sign of tire performance. 

Testing Real World Tire Pressures  

Why choose 35 psi and 17 psi? The VF Alliance Agriflex tires mounted on this sprayer are rated to perform at low tire pressures in the field—40% lower than a standard radial tire. With a load of 5,500 pounds on each tire, 17 psi is a realistic low pressure for these tires (on this sprayer) in the field. 

So what’s with the 35 psi? Nate Firle, chief agronomist at AgRevival, once told us a story about farmers and tire pressure. Back in 2021, when Nate was calling on farmers to talk about their agronomy plans, he decided to conduct an informal experiment. He brought a tire pressure gauge along. And, the first question he asked each farmer was, “Do you know how much air is in your tractor’s tires?” 

Firle found that 70% of the farmers he asked didn’t know the pressure in their tires. Outside of the 70%, a full 20% of the remaining growers knew exactly how much air was in their tires: whatever was printed on the tires’ sidewalls (the maximum inflation pressure). This is a great roading pressure, but not so great in the field. 

From our experience working with thousands of farmers, it’s pretty common for tires to be overinflated for fieldwork. So we chose 35 psi for the high-end pressure in this test. 

Study Results: Footprint Comparison

Before the Hagie hit the field with her new VF tires, we measured the tire footprints at both 35 psi and 17 psi. At 35 psi, each tire had a footprint of approximately 261 in². When we dropped the tire pressures to 17 psi, each tire’s footprint grew to approximately 348 in². That’s an extra 87 in² of footprint per tire—a 33% increase.

Study Results: A Field Day with High Tire Pressure

“Way cool” is what AgRevival’s owner and head agronomist Nate Firle said at the conclusion of our test. As in, the results were fairly enlightening. Our study was divided into 3 parts: 

1. A visual rut depth and surface soil condition test. 
2. A water infiltration test. 
3. A soil compaction test for severity and depth (using a cone penetrometer). 

Rut Depth

On the surface (literally), the sprayer’s tracks provide a clear visual of the importance of running low tire pressures across sensitive soil. With one side of the sprayer’s tires set to 35 psi and the other side set to 17 psi, Nate drove across some freshly tilled ground.   

The sprayer’s ruts measured 3.5 inches deep on in the high-pressure tracks. In the low pressure tracks, ruts were 2.5 inches deep. Is an inch a big deal? According to PTG, the supplier of the central tire inflation systems we sell, fuel economy gets 10% worse for every half inch your tires sink into the soil.

In the low pressure tracks, Nate could easily poke his finger into the soil and crumble the soil on the surface with his hand. In the high pressure tracks, he couldn’t crumble the soil; it was packed tight. And there was no way he was sticking his finger into the dirt easily. 

Soil Compaction

Using a cone penetrometer, Nate tested the amount of resistance it takes to push through the compacted topsoil inside the sprayer’s tracks. On the high pressure tracks, he needed over 300 psi to push through the compaction layer, which was 5.25 inches deep.

Inside the low-pressure tire tracks, he needed about 250 psi to push through the compaction layer, which was only 4 inches deep. As Nate remarked, “what you see on top [with the rut depth] is what is potentially happening within the soil.” In other words, the tires set to 35 psi, with their small footprints, had put enough pressure on the soil to turn it into a dense brick.

Water Infiltration Test

What happens when soil is compacted, much of the pore space is squeezed shut, and it comes to resemble a dense brick? It’s a lot harder for water and nutrients to move from the surface to the root zone, where your plants need them. The visual clue to this problem is water ponding on the surface.

So how much does water infiltration slow in severely compacted soil? For this test, Nate sunk two 6-inch-diameter PVC pipes 8 inches into the soil. This allowed us to test below the soil zone touched by AgRevival’s tillage implements to get a true picture of the soil profile. Nate sunk one pipe in the high-tire-pressure track and one in the low-tire-pressure track. He could then measure the time it takes for an equal amount of water to drain through the soil within the pipe.  

Nate’s goal was to simulate the water infiltration following a 3-inch rain event, which has not been an uncommon event in the Upper Midwest during the past several growing seasons. To do this, we poured 32 ounces of water into each pipe from scientific beer pitchers and watched the water start to bubble as it soaked into the soil and in exchange, air escaped from the ground. 

Immediately after pouring the water, there was about 1.5 inches of water in each pipe. At 5.5 minutes into the test, the pipe in the 35-psi tire track had minimal bubbling and there was still just under 1.5 inches of water in the pipe. At the same time, the pipe in the 17-psi tire track had just under 1 inch of water left in the pipe. You could also see air bubbles rising to the surface, which showed that the water was still infiltrating the soil. 

At the 20-minute mark, the high-psi pipe still had 1.25 inches of water in it, down from 1.5 inches at the start of the test. Not exactly draining fast! At the same time, the low-psi pipe had under 1/2 inch of water left. After 20 minutes, about half of the water had drained into the soil within the low-pressure track. 

The draining had continued in the low-pressure pipe at the 55-minute mark. Just under 1/2 inch of water was left. (Remember that we started with 1.5 inches of water.) In the high-pressure pipe, the water was still “all locked up.” The water level here was at 1.25 inches. 

Study Results: Low (Pressure) is the Way to GO

Yes, that’s a lot of data and observations to take in. But in the end, the conclusions were simple: 

• Your goal should be to run at the lowest tire pressures possible in the field if you want to safeguard a healthy soil structure.
• When you travel across your fields at high tire pressures, you risk turning your soil into a dense brick. Water (and nutrient) infiltration will slow. And, using common sense and data from past yield studies, we know that your yields will take a hit. 
• When you travel across your fields at low tire pressures, you’ll experience less rutting and less soil compaction. This can also translate to higher yields, better handling, and higher fuel economy.

Read More: Keep Farm Tire Pressures Low for Higher Profits

Improve Sprayer Performance with VF Tires

The question is, how do you get there? First, you pay attention to your tire pressures. And second, you work with technology on your side.

Advanced rubber compounds and highly technical sidewalls allow VF (very increased flexion) radial tires to handle more weight than standard radials. VF tires can carry 40 percent more load at a standard radial’s inflation pressure—or the same load as a standard tire at 40 percent less pressure.

VF tires are designed to operate safely and effectively with more sidewall deflection. As the sidewalls deflect, the tires will put down longer, rectangular footprints in the field. VF tires, set to the correct pressure for field operation, will help your sprayer: 

• Float over the soil, not plow through it.
• Improve fuel economy.
• Stay between the rows with less effort.
• Improve ride quality for less fatigue. 
• Have more days to spray. 

Optimize Sprayer Performance with CTIS

Sprayer tires live in two worlds: the road and the field. For the road, you need a high tire pressure to handle the heat from long distances at high speeds. However, you’ve just seen that a high tire pressure is the wrong choice for driving across the dirt.

If you try to compromise and choose a pressure somewhere between the correct road and field pressures, you’ll still cause compaction in the field. Plus, you’ll wear your tires faster, burn more fuel, and have to contend with poor handling while running down the road.

‍Learn More: A central tire inflation system is the ultimate way to optimize your sprayer's performance.

Only with a PTG central tire inflation system are you able to control your sprayer’s tire pressures at the touch of a button from the driver’s seat. This gives you complete control over your tire pressures: Set them high to safely handle miles of high-speed road travel, and then drop them to the ideal pressures for field work.

Thanks to Yokohama Off-Highway Tires, Our Study Sponsor 

Before we send you on your way, we’d like to thank Yokohama Off-Highway Tires for supporting this sprayer tire pressure study. At NTS, we serve farmers—not a particular tire brand. After all, your farm’s goals and budget and preferences may look completely different than your neighbor’s. However, if you spend any time on our PTK blog, you’ll notice that Alliance Agriflex tires are often near (or at) the top of our best-of lists. Why? Our customers have good luck with them. They’re top-tech tires that offer an enticing balance of performance and value, with a 10-year warranty to boot. 

Talk To a Tire Expert to Put Your Sprayer on the Best Track

You don’t have to put up with poor sprayer performance. Yes . . . you can fix the bad handling, the bad ride, and the pizza-cutter ruts. And you don’t need to be a tire expert either. Click the blue button below to talk with a tire expert about the best options for your farm, whether a set of VF tires will do or if your sprayer would be even better off with CTIS. We’re here to help Drive Your Farm Forward with the right tires and wheels on all your equipment.