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t seemed like their semis almost always had two axles on the truck itself, while I had invariably seen three here. Does anyone know anything about that?
This is about having two drive axles. Normally, one only uses the axle designated as "the drive". The second is disconnected under ordinary circumstances until one is on uneven ground that the rig as a whole cannot traverse. Then the driver uses a dash switch to "lock" the differentials (not a locker diff as with 4WD pickups; a manner of speaking) so that both are accepting engine power.
Trucks are easily hung up. That long wheelbase (in comparison to cars, say) can place the tractor in a position that at low speeds causes "the drive" to be suspended in air. There is only so much "give" between tractor and trailer at the point of the hitch (the fifth wheel).
Yes, some O/O's are spec'ng single axle tractors for highest FE today. But those are on-road only. Understand that many, many, many big truck parking lots, service facilities and the rest remain unpaved (as they are easier to maintain) thus necessitating two drive axles. Plenty of customers also have hard-to-traverse locations as well.
I was unloading fly ash at a site near the Houston Ship Channel a few days ago. An "environmental company" was drying out a swamp pond thus the 125T's daily of this power plant product delivery. A truck that came in after me was backing around a 110-degree corner, and tried to pull forward with the Steer Axle over the edge of the temporary road. Knew my day was screwed once he had even one Drive in the air as I was trapped. Took quite a while to get a trackhoe back to his position to pull him back up around corner so he could regain traction enough to back into position.
This second, or third, life of a former company OTR truck is part of "the truck economy" in this country (construction, big maintenance projects, etc) and owners can't afford a single drive tractor (and refits aren't cheap). Resale value is part of the original owners calculations.
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