Running Above the Governor

Which circumstances are you referring to with this statement?

 

I will differ with you on this point. If you do not have a governor and you still have throttle at 75 mph, there is nothing wrong with cruising down the hill at 75.

However, even with jakes engaged, if you have no throttle left, you also have nothing left to pull a wayward trailer back in line with. If (as said earlier) some external force causes your trailer to sway, what are you going to use to give it a little tug and pull it back in line?

Some here will say they'll use the johnson bar. All well and good unless you don't know how much trolley brake to use and, again, circumstances. Too much johnson bar and you will have a rollover. (For those who do not know...and there are a few...the johnson bar controls your trolley brake.)

 

Simple physics will prove you wrong on the first point, but I'll start with the second since it comes first in the scenario.

A driver for Knothead Trucking has a truck governed at 65 mph. Thinking he will make up some extra time he spent in Rawlins, he chooses to let the Sisters help him out a little. (We'll use a nice, long, straight hill) He's running a reefer trailer, so he's a little heavy. We'll say 42K in the trailer.

As he's going down the first of the Sisters, he's lettin' her roll, has an eyeball on the road ahead and checking his mirrors, everything looks pretty good. Since he's in Wyoming, we'll say he gets hit by a pretty good gust of wind unexpectedly and has to steer into it a little bit to stay in his lane. As a result of his corrective steering, which we do thousands of times every day without even thinking about it, his trailer responds in like manner. It sways a little. Seeing this, he tries to hold it steady, but it's going out a little more than he's comfortable with.

He tries to steer back the other way just a little teeny bit to get that trailer back in line. At the instant he's trying to pull it back in with the steering, he feathers the brake pedal. This engages his tractor brake, but there's a half-second delay to the trailer brake because the air pressure needs that little delay to build. Since the trailer is three times heavier than the tractor and it is already in a sway as the brake engages on the tractor, it continues its arc and becomes a real problem.

Newton's Law of Inertia tells us that an object in motion will remain in motion unless acted upon by an unbalanced force. Due to the gust of wind, the rear of the trailer is no longer in line with the unbalanced force (tractor brake) required to stop its motion. Since Knothead Trucking decided to govern its trucks and this driver was in a bit of a hurry, there was no force available to realign the heavier object behind the lighter object which actually contains the necessary unbalanced force to stop the two. As a result of that lack, the heavier object (rear of the trailer) spins around the slowing lighter object (tractor) and causes either a complete rollover or a jack knife. Either way, at 75 mph, this driver and anyone around him is likely dead.

Had he been a couple miles an hour under his governor, he could have goosed the throttle a little, pulled the trailer back in line and then feathered the brake. However, when he hit the brake, the trailer was already moving to the side and he had fewer choices available to him to correct the motion.

Regarding ice, I won't go into the number of supertruckers I've personally seen hauling tail on ice. Ice isn't even part of this discussion.