AKRON-``Underinflation'' a good thing? Tire manufacturers and dealers have long since harped on the dangers and rubber-eating effects of underinflated tires.
But a growing trend in the farm industry is demonstrating that inflation pressures as low as 6 psi-well below those marked on the sidewalls-are not always bad.
In fact, industry experts and engineers say properly ``underinflated'' tractor tires can increase crop yield rates and eliminate dangerous tractor ``power hops.''
The key is to match the tire's carrying capacity to the load it must carry. In many cases, farmers operating their tires at 20 to 24 psi are using two to four times as much air as is needed.
For years, farm tire makers have been computing and releasing tire load/inflation pressure charts to help dealers and farmers optimize their tires' footprints. Traditionally the lowest pressures on those charts sat around 12 psi.
Recently, however, manufacturers have been advising farmers that-under the correct load-their tires can and should operate with pressure as low as 6 psi.
In general, less air pressure allows tires to sag into a larger contact patch. Larger footprints increase traction and pulling power as well as disperse the vehicle's weight over a larger portion of ground reducing soil compaction.
The key, said Goodyear's L.B. ``Larry'' Hurst, farm and terra tire manager, is to keep a sufficient amount of air in the tire to support the load it is carrying.
``You can't just go out and deflate your tires,'' he warned.
More efficient tires also wear at a better rate, improve fuel efficiency, ride comfort and can even increase the number of acres worked in a given period of time, according to Len Walker, sales engineering manager with Bridgestone/Firestone Inc.'s Firestone Agricultural Tire Co. subsidiary.
Less compacted soil, in turn, provides a better growing environment for crops.
Larger contact patches also allow for greater traction, which can
help stop front tires from the gripping-and-slipping phenomenon that creates power hops-violent jolts experienced after torque builds up in radial tires.
The idea of using ultra-low pressures in farm tires is not new. Trelleborg Industri A.B. has been developing, manufacturing and marketing its low-pressure tires for more than 30 years in Europe.
Trelleborg's Twin tire utilizes both cross-ply and radial belts to increase the sidewall strength of a tire at extremely low pressures-down to six or seven psi in some cases, said Christer Rosberg, market manager-pneumatic tires.
Trelleborg said its tires can increase yields by 5 to 20 percent.
About three years ago, Trelleborg began exporting its low-pressure tires to the U.S. market. Since then, demand for the tires has been so great the company's U.S. subsidiary, Trelleborg Monarch Inc., could sell twice as many tires as it has, Mr. Rosberg said.
The firm, he added, is looking at the possibility of manufacturing in the U.S. to increase supply.
Still, engineers at other tire manufacturers say their tires can be run on the same low pressures with the same results.
According to BFS' Ken Brodbeck, product engineer, tire testing, in order to properly maximize the contact patch for a farm tire, operators must first:
Determine the total axle load-including cast or liquid weights, tanks and implement hitch weight-using a grain elevator or calling the tractor dealer;
Divide the axle load by the number of tires on that axle; and
Use a load/inflation chart to determine correct pressure and inflate the tires to that pressure.
It is important, he noted, to check the tires on a weekly basis since even a small deviation from the intended pressure can cause underinflation when working with pressures as low as 6 psi.
Operators must also make sure their tire gauges are accurate. ``Checking with a gauge that is off by 2 psi can lead to serious tire durability problems when setting tires at these lower pressures,'' BFS' Mr. Walker said.