Gator398 wrote:
Here's an update: front tires are at 65, rear duals are at 60, just took the TT on our first long haul 1200 mi total. I will weigh tomorrow when I fuel, the ride was awful most of the time until I passed OK state line, so this is a road problem. Only on Oklahoma highways so far have we driven in these concrete "expansion joint" highways I believe they are called, where every section is raised a bit and results in a constant "tha-thunk tha-thunk". So far the costly toll turnpike to Hugo was the worst and nothing but smooth roads (occasional rough patches as normal) since, we just crossed into Alabama tonight.
Edit: Also this is not a daily driver so I would appreciate advice on towing conditions only. 30psi in rear on stock size tires when towing, with road temps rising now, is asking for a blowout at 75mph. All valid points about lowering pressure to improve ride but don't forget while towing, this raises heat fast in summer causing tire failure if not pulling over frequently enough to let them cool.
The biggest issue with what you described is not tire pressure but concrete roadways with the control joints cut symmetrical. Concrete does “swell” eventually at exposed joints. More so on cut or cracked joints as that surface is more permeable.
If the joints are spaced evenly they can/do initiate a harmonic pattern in some vehicles.
Stiff suspension ( and tires but you’d have to run them pretty soft to overcome at highway speeds), wheelbase length and weight transfer off the front axle (like towing a trailer or loaded pickup bed) exaggerate this effect.
However, back to tire pressure, no one is suggesting 30 psi in your duals while towing, or are they? Load pressure chart for 235-80-17s gives you 6900lbs of capacity for 4 tires at 35 psi. What does your rear axle weigh? You pull a TT so not very heavy on the truck axle comparatively. If you had 4 large passengers, 1000lbs of gear in the bed and 1500lbs tongue weight, you still wouldn’t break out of the available load capacity of your rear tires at 35psi.
At a very small theoretical penalty in fuel mileage due to rolling friction, running the “proper” pressure for the load will always yield the best ride, general handling characteristics, traction and minimize tire wear. And you’re running 10klbs worth of air for presumably waaay less load than that. But icbw on you axle loads.