Looking at the MAFCA "A" of the Day for 2/15, I've always wondered at how much the big A trucks could pull or haul.
With a raging 40 HP on tap, could those big Gas Tankers, Stakebeds and Dump Trucks in anyway keep up with ever moderate traffic when loaded?
Does the foot actuated ****** switch help anywhere except when you need tree climbing gearing and torque?
Trucks were engineered and built differently then - for moving heavy loads from point A to point B, and not necessarily very fast, even by 1930 standards.
Take a look at the Mack AC "Bulldog" (1916-1938), which were chain-drive to the very end , and had solid rubber tires on cast-steel wheels through the late 1920's. They rarely moved faster than 20 MPH, if that.
And getting that load stopped was another concern !
Long-distance transfer was done by rail, with the trucks carting loads between the shipper and the local rail-head.
The big trucks, like the Mack Bulldog, GMC "Big Brute", Packard, White and such were "heavy-duty" trucks, with capacities ranging from 3 to 15 tons.
Trucks in the 1 to 2 ton range were considered "medium duty" ( with a single rear-axle).
As for the "Raging 40 HP on tap", remember, it's TORQUE that moves things (especially from a dead stop!)... with the proper gearing ( and traction), you can pull huge loads with relatively low HP... the only HP spec I could find for the AC Mack Bulldog was from about 1928: 4 cyl= 60 HP @ 2200 RPM. Couldn't find any specs on Bore/Stroke or displacement, but I have seen a few of these in person, and the engines are huge, probaly 300-400 cid.
Another factor was the condition of the roads you were hauling over... try to go fast with an overloaded truck on winding / bumpy / washboard roads, and you'd probably break springs / blow tires ( remember 1930 "Rag-tires"), or possibly roll the truck on its side...
With the advent of improved , paved roads in the mid-to late 1930's, Over-The-Road trucking became a practical alternative to rail shipping, and the power / speed of big trucks increased.
All that said, I wouldn't be surprised if a stock Model AA could repeatedly pull two to three times its rated capacity... but top speed would probably be a bit lower than it's un-loaded top-speed....