Originally Posted by CrawfordGene
The question that never has been answered and I ask it every couple of months on one tire thread or another: why do auto and truck manufacturers always recommend less pressure in the OEM tires than is stated as maximum on the sidewall? Or, another way, why wouldn't they recommend maximum sidewall pressure if it is safer?
I am assuming (because I didn't read the linked thread) that recommending maximum psi stiffens the sidewalls and that is why we should run a maximum. Is that correct?
My understanding about tires has always been the load/pressure relationship. For a tire to have the longest life, greatest reliability and best performance in braking & handling, then a tire properly rated for the GVWR (and a bit more; why axle WR combined is higher than GVWR) must have an adequate reserve capacity, first. Second is that to find the best pressure was to weigh the vehicle and use axle averages to set pressure against the manufacturer Load & Pressure Table (not ever going over or under the Vehicle
manufacturer recommendations) and adjusting for changes in climate & terrain as necessary; hot weather to cold weather.
The vehicle manufacturer doesn't want you to have an unnecessarily hard ride, nor to transmit extra shock to the vehicle. Shock absorbers have their [important] role, and chassis bushings theirs. It is all supposed to work together. We change the pressure mainly when we change the load, and that's the only "good" reason (is a way of seeing it).
Trailers, mainly at low speeds, experience sidewall deflection differently than cars or trucks. They can wind up with one or more tires really pushed hard into a position. Certain kinds of turns, and a heckuva lot of parking. Sometimes it is not obvious. On tandem and tridem axle trailers this is more of a concern.
Going down the road the TT is never master of its' fate
, so to speak, as is a car or truck. It is always being pulled (it could be pushed, also) and the forces that allow a car, say, to "relax" don't work out for something at the end of a 20' pole pushing or pulling it (as it is almost not ever perfectly aligned with the force pushing on it). And then it sits having been levered into that position. Days, weeks, months.
And the transient thing I tried to do above. Sideslip angle
is when we get into the forces acting against the trailer to lose it's grip on the road. Markdoane
made reference to one of Bundorf's SAE papers  in a post/thread a few years back (that is good reading). Stiff sidewalls make for longer life and predictable road manners is, again, my understanding (even if it is only information posing as knowledge).
Philosophically, I'm interested in the worst-case scenario: tired, ill, injured driver on dark night, in rain, inadvertantly at too high a speed. Broken or potholed pavement coming up (unawares) with a-hole drivers around the rig and the need for hard maneuvering coming up. Braking. Downshifting. All the dice rolled. So, hitch, tires, vehicles are not what I want to worry about having made compromises upon, and am now reliant on driver skill to get me out of it. Confidence
cannot be overstated, and it is
my experience (personally and professionally) that this confidence in the rig itself that gives the margins one needs (for lack of a better term) when the moment is upon us.
I may say that I will not ever drive under any one of those circumstances, but it is my preference that rig and driver perform admirably if called upon to do so.
So if the tire engineers are adamant, I'm fine with it. Tire quality via brand is more my interest now (as a method of determing size and load has better tools available). Henceforth I want to ask my questions from established baselines, hitch rigging or tires. Numbers. No different than in engine performance parameters.
That's the best of my understanding. Jammer would do a better job.
I don't know if I ever looked at your older Silverstreak so I clicked on the link. It was beautiful! It must have been very hard to part with it. Did you get all the work done around the house when you removed the SS temptation?
I got as much work done around that house as budget allowed. And a bit more. Things changed quite a bit for us over just a few years. I did repaint the exterior in a job I was quite proud of (revealed details formerly hidden). Letting that trailer go hurt to some extent, but a rear bedroom model was greatly desired, so a combination of circumstance, opportunity and different responsibilities made selling it a fairly easy decision.
Glad you liked it. A nice one for condition when we bought it, and the renovation showed it off nicely. Thanks. They're an excellent choice when an otherwise original one can be found.