Apparently farmers are being told conflicting things about tractor tire pressure. After reading our recent story about tractor tire pressure, readers called in to say their tire salesmen had warned not to decrease pressure or the tire warranty would be void. Of particular concern was advice in our story that recommended tires could be deflated to as low as 6 psi.

We checked with Firestone. Here's what Jay Wheeler, an ag tire engineer at the company, had to tell us.

"We do show inflation pressures as low as 6 psi for radials in our application books but nothing lower than that. The main thing to remember is that the load carrying capacity of the tire is greatly reduced with the lower pressures. If the weight is reduced to the proper level then there should not be a problem. But, if the weight can't be reduced enough it may take duals (or triples) to get the loading right.

Obviously the loads do change with mounted implements or spray tanks attached. When low pressures are used on an overloaded tire it causes excessive flexing in the sidewall that could lead to premature failure. Then there is the possibly of doing damage to the tire (or rim) if a sharp object (rock or other) were hit with an under inflated and overloaded tire. We preach that the optimum footprint is achieved when air pressure is matched to load and that inflation pressure can be changed to match load accordingly. The trick is to know the load first and adjust pressure to match.

As with any product, most warranties are not set up to cover factors beyond the manufacturer's control."