It had no sleeper, so I assume it was for local/regional deliveries. Instead of the typical dual rear wheels, it had a single, extra-wide rear wheel and tire. Moreover, the front axle of the tandem rear axles was up off the ground. I'm guessing that axle is dropped down when pulling the trailer. I couldn't tell for certain if that axle was also powered.

Ive seen those, some pulling a fuel trailer,

also seen some trailers that the front set of tires were off the ground as well,


all to reduce rolling friction I guess

As I understand it, that lifted axle can be lowered when necessary (heavy weight aboard) and lifted when the truck is unloaded — as lyman says — to reduce rolling friction (resistance).

The extra-wide wheel/tire is referred to as a “super single,” — I remember asking about that arrangement here a while back.

Here is an article on some pros and cons, as compared with the usual dual-wheel arrangement.

Instead of duals, they put on super singles!!
Pain in the ass. One flat and your screwed. With duals you can limp for a bit, singles your fucked! My company in it's infinite wisdom even stopped putting dollies on the tankers, one flat tire required two big wreckers. Maybe five grand for a flat. That ended pretty quick.

Also helps with load restrictions. Some roads are limited by the number of axles/tires the vehicle uses.

If they are hauling empty and have the wheels/axles lifted, it allows for a better route to be available based on these restrictions.

The Super Single can also make it more exciting while driving in the rain.

quote:

Originally posted by .38supersig:


The Super Single can also make it more exciting while driving in the rain.

I'm glad I never found out. A coworker buddy jacknifed on Singles, lost the load, shut down I-75 for three hours

Yeah, our ranch truck had six super singles on it when we bought it. We set it up as a rolloff and built multiple bodies for it: a 4,000 gallon water tank with motor, pump, and spray system, a trash body (20’ seatrain container with the top cut out, a 10 gauge floot welded in, and the doors chained back, a rock body with pneumatic locks and lift for the tailgate, all with a rolloff hitch on the front and rolloff rails. Only dumped a couple of loads out of the rock body with super singles on the rear two axles before I bought four rims and recapoed tires from a trucker buddy. The truvk is orders of magnitude more stable when dumping with duals on both driving axles. It’s nice having super singles on the front axle (a Fabco 20k lb, selectable driver), but I wouldn’t ever out them on the back.

quote:

Originally posted by .38supersig:
The Super Single can also make it more exciting while driving in the rain.

I’ve wondered about that!
That big ol’ contact patch has to be great for traction in the dry, but also must suck for hydroplaning in the wet.

I had drivin many different rigs and construction trucks years back. Of the construction trucks, mainly tri axle dumpers for aggragates, that raised axle is called a tag axle. It is lowered to the road by air bags. If you know a typical 18 wheeler is 70 feet long and can gross 80,000 pounds, a short little tri axle, fully loaded weighs 72,000. That's why the tag is needed to balance the weight. They are generally raised for cornering but, more modern dumpers have steering third axles.

I especially wouldn't have singles on a tractor,
no flippen way! I value my life more than my company does.