I've been watching this thread for a while and frankly, most of the info in it regarding overinflation and tire safety, is malarky.
I've raced cars and been around people at the highest levels of motorsport since the 1980s, talked frequently with tire engineers, and after reading this last night, wrote a friend who's a tire engineer and discussed this thread, as well as compared notes on our experiences with trailer tires over the years.
First of all, tire durability is overwhelmingly related to running temperature. Running temperature goes up because of flexing in the tire carcass. The higher the pressure the less flexing and lower overall tire temperatures (especially in radials).
Tires have about a 3x safety factor in inflation - you can put more than 90 psi in a 32 psi rated tire when new and it won't catastrophically fail. Therefore a reasonable amount of cold overinflation combined with an expected amount of hot pressure increase is not going to cause failure. This is especially true when running at high speed in hot (desert sunny) conditions. I have an old college roommate who used to work the oil fields in Saudi. They used to run standard passenger car tires (32 to 36 psi) at 45-50 or else a blowout was a serious risk (they frequently ran over 100 mph out in the boonies).
I don't know what police departments do, but when I autocrossed cars we used to put 45 psi or more in higher profile tires (this was before 50 series were widespread) to keep the tire on the rim at high cornering loads - you have to stiffen the sidewall on a radial with more pressure when running at extremes or bad things will happen. Bias tires are not as much of a problem.
That's not to say there aren't tradeoffs. Inflation pressures for a given tire manufacturer and size are designed to produce a footprint that maximizes traction and durability under normal use. Raise the load and you need more pressure to maintain that footprint and lower running temperature. If you overinflate the tire it "beachballs" and reduces the load on the outer ribs, increasing the wear on the center of the tire. Because the footprint reduces in both length and width, traction capacity goes down.
If you really want to know how happy your tires are you have to get a contact pyrometer and push the needle into the tread blocks and look at temperature across the surface of the tire IMMEDIATELY after a half hour or so of intended use. For something like trailer tires and rear tires of a MH or tow vehicle, the temps should be within 10 degrees or so across the tread and consistent across all four tires - or else you have a loading issue or alignment issue. On front axles, they should be 20 deg or so hotter on the inside edge than the outside - this is due to camber. IR non-contact pyrometers are useless
in this application. I'd guess they ought to be under 175 deg, but I haven't found a reference. Race tires run over 200 deg. I've commonly seen 235!
What is not BS is the warning on rated speed. I frequently pull my trailers at 75-80 with the truck, but no more than 65 with the MH. OUT here in the Mojave, it's HOT. On my old toyhauler I went through a set of Goodyear Marathons and a set of Denman STs with 7 belt failures. On my current trailer, I had almost two years of use with no noticeable tire wear using the standard cheap chinese junk OEM tires - all towed behind my MH. Then I took a a fast trip to Tucson to pick up another race car, towed it with the truck. Got home and the front two tires on the trailer are now neither round nor flat across the tread, with heavy wear on the inside. NONE of these tires were run underinflated or overloaded - in fact, they were about 20% under max load.
When I compared notes with my tire engineer friend, he indicated after 20 years of no problems with Firestone 440s, he switched to carlisles and had a blowout. Failure analysis showed no signs of rubber adhesion in the cords - a sign of poor manufacturing quality. He's now using made in USA LT tires on his trailer, rated at 44 psi but inflated to 50 to add lateral stiffness and make them run cooler - because while the LTs don't offer the sidewall protection of an ST, they are safer at highway speeds. I'm now considering going that route or the one below.
A previous post included links to the GY RV guide - but that's not the only GY reference out there - see:
An interesting tidbit in there:
"Special Trailer (ST) Tires
Goodyear Marathon trailer tires are widely used in a variety of towable trailer applications and are designed and branded as ST (Special Trailer) tires.
Industry standards dictate that tires with the ST designation are speed rated at 65 MPH (104 km/h) under normal inflation and load conditions.
Based on these industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph (106 km/h and 121 km/h), it is necessary to increase the cold inflation pressure by 10 psi (69 kPa) above the recommended pressure for the rated maximum load.
Increasing the inflation pressure by 10 psi (69 kPa) does not provide any additional load carrying capacity.
Do not exceed the maximum pressure for the wheel.
If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 mph (104 km/h).
The cold inflation pressure must not exceed 10 psi (69 kPa) beyond the inflation specified for the maximum load of the tire."
To the original poster, your mileage may vary, but it appears a ~10-20% overinflation will increase speed margin but not load margin, and have no other adverse effects on safety.