Assuming something other than an entire axel’s worth of tires going, how many wheels could an 18 wheeler lose and still operate reasonably safely?
Thre’s no simple answer to your question and laws vary by jusisdiction. Generally you’re allowed a max. of 18k lbs. per dual axle and 34k lbs. per tandem axle group. Most states allow for “singling out” (running w/ one wheel removed from a set of duals) if you’re under a certain gross weight. I’ve done this, but only in situations where it’s necessary to get to a place where proper repairs can be made. It’s important to keep tires inflated to close tolerances to prevent heat buildup, which can cause a blowout and of course, uneven tire wear. As little as 4-5% difference, between dual mounts, can have dramatic effects.
The laws are specific and a truck may be placed out of service (unable to move) until weight requirement are met.
Oh, I’m not talking about legally, although that’s interesting.
It’s going to depend on the load - you could probably drive with only the two outer back corner tires on a trailer if the trailer was empty.
On the tractor, you might be able to get by without the inside wheels of either or both rear axles, again, if the trailer’s lightly loaded.
But I sure wouldn’t want to be anywhere near this truck. There’s a reason truckers have to follow a whole bunch of laws regarding safe operation.
It’s possible to ‘chain up’ one end or both ends of an axle on a trailer with tandom axles as an emergency repair. I have had to do that a few times. What I mean is, you can use a chain to pull an axle up to the top of its spring travel and secure it to the frame so that the tire (or bare hub) is not in contact with the road. The other axle in the tandom can carry the load, if it’s not too heavy.
There are some trailers with air bag suspensions that are designed to do this in normal operations. When the trailer is empty, the suspension can be deflated, raising the axle and saving wear on four of the tires.
I’ve seen the same sort of thing on tour buses. Is there really enough savings in tires to justify the complexity of a mechanism to lift an axle off the road? On a bus I saw this in action, it looked more like a motorized (hydraulic?) operation to raise and stow the wheels, rather than just picking them up a few inches and letting them dangle.
The mechanism is really not complex; it’s already part of the suspension. The suspension has an air bag anyway, acting as a ‘shock absorber’ or damper. The normal operating position is with the bag pressurized, pushing down on the spring. To raise the axle, you just stop pressurizing the bag.
You see this quite a bit on dirt and rock hauling dump trailers around here.