wcjeep wrote:
With my G rated tires I run 60psi front/ 55psi rear when empty. 75psi front/110 psi rear when heavy.
That "55 psi" caught my cautionary eye.
That might be too low for the tire to be safe to reinflate to "110 psi when heavy" without removing the tire and wheel and putting it in a safety cage first.
For your own safety, please check the load inflation table for your specific tire, and pay particular attention to the MINIMUM inflation specs for that tire.
This can be critically important in 19.5 tires, because unlike 18" tires of the load range E variety, the 19.5 tires in load ranges F, G, and H have a steel cord in the sidewalls. That steel cord is part of the structure of the tire that enables it to attain both the load and pressure ratings on the maximum end of that load inflation table.
When a 19.5 tire is under inflated below the minimum pressure rating specified, the sidewall flexes too much, both in amplitude and frequency. The frequency at highway speeds is an average of 640 flexes per minute, Take any thin metal wire, and bend it back and forth 640 times. Like flexing a coke can back and forth, the wire will separate from metal fatigue. That is exactly what happens to each one of the wires that makes up the steel cord in the sidewall to a 19.6 tire.
After running around for miles unloaded at only 55 psi, it is possible that the steel cord in the sidewall may have become weakened. The weakness may not be observable at 55 psi. The problem occurs when you suddenly go and double the pressure again to 110 psi. People have DIED from doing this. This is why mankind came up with the idea of making safety inflation cages, which are found in every reputable tire shop that knows how to handle heavy truck tires.
It is ok to adjust inflation pressures on a 19.5 tire while mounted on the truck without using a cage, as long as the range of pressures has remained within load inflation table for that specific tire. But if the tire is found to be flat, or known to have been run in a severely underinflated state, it can be very dangerous to re inflate that tire, due to the higher probability that the steel cord in the sidewall was over flexed, which potentially fatigued the metal, leading to a sudden zipper failure when re inflated.
I highly recommend maintaining the minimum inflation pressure indicated by the manufacturer for the 19.5 tires you run. More information about this issue can be found by searching the internet. You might find many of my posts on this issue over the years, on different forums under different user names, so I recommend searching the tire manufacturer's websites directly, to avoid hearing more from this lone voice in the desert.
Other resources to learn from are the Tire Industry Safety Council, as well as the Rubber Manufacturers Association. Theses agencies were largely responsible for the campaign to mandate an unwilling automotive industry to include tire pressure monitoring systems on lighter vehicles. And we are all safer on the road because of it, as people are now alerted to when one of their tires are under inflated. Not everyone does something about it, but enough people (like my wife) DO pay attention to the dashboard warnings, and that has been a good thing for not just her, but for all who share the road. Safe rolling!
