The Firestone Farm near Akron, Ohio, tests agricultural tires – not only its own Bridgestone and Firestone ag tires but also tires from the competition.
In one of the company’s test labs resides a giant wheel-tire assembly spinner. While it appears similar to a tire shop’s digital balancer, it doesn’t perform that job. It measures a sometimes dangerous and damaging form of ride disturbance called run-out. This out-of-round wheel-tire problem mainly affects farm equipment at transport speeds.
Firestone tire engineer Ken Broadbeck said the machine is for designing new tire technology and for training demonstrations.
Read Also
VIDEO: Green Lightning and Nytro Ag win sustainability innovation award
Nytro Ag Corp and Green Lightning recieved an innovation award at Ag in Motion 2025 for the Green Lightning Nitrogen Machine, which converts atmospheric nitrogen into a plant-usable form.
“Just today (May 21) we had dealers from New Zealand using the machine,” he said.
“With tractors going faster and faster, the wheel-tire assembly must be round so you don’t get a ride disturbance at road speed. You can mount and re-mount tires all day long and still get road lope if the wheel hardware isn’t round.”
Broadbeck said the unit’s computer system can pinpoint where a wheel and tire assembly is out-of-round by looking at the tire and hardware to which it is mounted. The lab device is precise enough to pick up a bent axle if that’s the problem.
Tire experts say centring a wheel and tire doesn’t require complicated science, and producers can achieve similar results through careful wheel and tire mounting.
Balance can usually be obtained by allowing the big rim to centre itself as it freely rotates while the lug nuts are tightened in a crisscross pattern and by not letting the weight of the machine come to rest on the tire until all lugnuts are tightened.
Significant problems such as road lope can be created if farmers follow the common practice of tightening just two or three lug nuts and then lowering the machine to the ground to tighten the rest.
Broadbeck said during his 15 years in the agricultural tire business he has noticed that the problem often isn’t apparent until equipment is moving above 28 km-h.
Michelin agricultural tire specialist Bob Rees said producers can inadvertently create an out-of-centre situation any time they change tires. It can happen when installing duals or triples, replacing tires or switching from one set to the other on a high-clearance sprayer. It can also happen on an on-farm grain truck or highway semi.
Reed Turner, an engineer with the Alberta AgTech Centre in Lethbridge, said road lope can be temporary.
“You get temporary road lope with radial ply tractor tires on a cold morning. The tractor porpoises down the road for a while, but once the tires warm up, the road lope goes away.”
Turner said if road lope doesn’t disappear as the tires warm, then the obvious problem is an out-of-round wheel-tire assembly.
If the assembly is off centre on the hub, it’s easily fixed by loosening the lug nuts and centring it properly. However, on some occasions the tire has been manufactured out-of-round and needs to be replaced. In other instances, the wheel might be bent.
“Either way, the only way to fix it is to make things round again,” Turner said.
Rees said that every wheel-tire combination has a natural, underlying vibration frequency. Sometimes, a component in the drive train of the machine will be sensitive to that specific frequency, causing it to resonate through the entire vehicle. Checking to see that all wheels are centred can often fix the problem.
Rees said duals on tractors sometimes create an easier challenge.
“We’ve found that if you get road lope or if you get excessive vibrations with duals, you can re-set just the four outer tires 180 degrees from their current position. That by itself often solves the problem.”
Rees agreed with Turner that sometimes the tire is out of round. He said bias ply agricultural tires, by their nature, are not manufactured with the inherent quality of radials.
“The design of the bias tire does not lend itself to good uniformity. Plus it has a stiffer sidewall and that can amplify problems. The design of any radial ply tire gives it a more uniform circumference. That means it performs better and is less likely to cause you problems.”
Vibration can also pose problems on tandem trucks and highway tractors, said Michael Burroughes of Michelin. He said there will always be some degree of play with the hub pilot centring system.
“I personally think the stud pilot was the perfect mounting system because the guidance of the stud would draw the wheel in uniformly as you tightened the wheel in a crisscross pattern.”
He said the taper on the nut automatically centred the wheel.
“Unfortunately, the hub pilot mount has become the prevalent mounting system, especially for duals on trucks, so they no longer need left hand and right hand threaded nuts. But we’re seeing more centring and uniformity issues with hub mount systems.
“That’s why a lot of truckers change the steering tires while leaving the rim bolted to the hub. Once they get the truck set up with that sweet spot on the front end, they don’t want to upset the apple cart by unbolting and removing the rim. They want to keep that exact perfect marriage of wheel and hub.”
Burroughes said the simplest way to check for out-of-round tires is to jack up one corner of the machine so the tire rotates freely. Set up a heavy object near the outer circumference of the tire or clamp a straight iron to the axle and set it a half-inch from the tire. Turn the tire by hand while visually checking the gap between the tire and the stationary object.
