General comments.
Unless we want this thread closed let’s keep our comments to tires, axles, inflation, and equipment and not about posters.
Now as to speed limit ratings.
Speed Ratings are a maximum the tire can be expected to operate without suffering damage. It is much like the red line speed for the vehicle engine. It can be exceeded but at a significant cost to the durability of the engine or tire. So if you choose to drive at speeds faster than 65 with your ST type tires you should not be surprised if you suffer premature failures.
ST type tires are somewhat of a special case in that T&RA specifies a max speed of 65 mph for these tires. Passenger and Light Truck have a number of possible speed ratings listed in T&RA and the tire manufacturer sales & marketing departments specify the various performance criteria they want a tire line or size to have. The tire engineer’s job is to balance all the variations and contradictions and develop a tire that meets all the specifications requested.
DOT has published test criteria for speed, strength and endurance that are based on the loads & inflations as published in T&RA. DOT does not have or specify the various speed ratings we see in Passenger & LT tires. Those come from SAE.
If a tire is marked as an ST type it has a single speed rating and that is 65 mph.
Unlike car and truck manufacturers there are essentially no tire development program or performance specification criteria for tires within the RV industry. This costs money which the RV manufacturers are not willing to spend. Tires are a commodity just like nuts and bolts. The RV manufacturer decides what size and strength (load) they need and then shops for the lowest cost option. For trailers this is most often an ST type tire.
There are a couple exceptions to this with one being a very heavy trailer that needs a commercial low platform trailer tire that has a 62 mph speed restriction.
Federal law states in 49CFR571.120 S5.1.2 .....the sum of the maximum load ratings of the tires fitted to an axle shall be not less than the gross axle weight rating (GAWR) of the axle system as specified on the vehicle’s certification label required by 49 CFR part 567."
So most of the time the RV mfg does the minimum required by law (lowest cost) and selects a tire that just barely exceeds the GAWR their marketing dept thinks they need so they can sell the trailer.
That is why we get tires with no reserve load capacity.
Now as to the max inflation. That gives the max load for the tire cost so again that is why the RV mfg specifies the infl. to equal the max on the sidewall.
I doubt that there is a single RV manufacturer that realizes there is a good technical reason to specify the max inflation for multi axle trailer use.
