Truck Jumping

click for a close-up

My first truck was a 1950 Chevrolet – probably around 1958. While it was not my first vehicle, it was most certainly among the most unique. It was yellow, heavily used, and seriously rusted. The bed, including the side panels and tailgate, had been replaced, and the donor vehicle had been a red GMC pickup. If you saw mine coming toward you, you would say it was a yellow Chevrolet, but from the rear, it was red with a very large GMC embossed on the tailgate.

The other thing that made it unique was that both red and yellow halves had rusted to the point where all the metal, where the body bolted to the frame had rusted away, leaving the passenger cabin[i]“Dog House”, as it was then known to bounce around, particularly on country roads. Attempting a sharp left turn was particularly troublesome because the body would tilt to the right and jam the peddles in place. The only solution then was to switch off the engine and let it coast to a stop – get out, go around to the passenger side, and push the body back up on the chassis. That was most troublesome in heavy traffic, which fortunately was not a problem in Three Rivers but extra care would be needed in Kalamazoo.

I have owned a half dozen or more trucks since then and my current one is a 2013 RAM, four-wheel drive. The table below describes some of the features of the 1950 Chevrolet/GMC, which I jumped out of many times as a teenager, comparing it to the RAM, which I jumped out of only once.

There is only a couple of inches difference in the bed heights of the two trucks, but my launching point, on top of the RAM toolbox was 9 inches higher than the Chev/GMC bed, making the impact velocity[ii]While it is not possible for a human to reach Terminal Velocity by jumping out of a truck in a Home Depot parking lot, I can attest to the fact that it feels “terminal” when you hit the pavement. a bit higher.[iii]Ignoring wind resistance, the velocity is independent of weight. The big difference, however, is in the deceleration time – assumed to be half in the case of the asphalt parking lot, vs grass and sandy soil at Fishers Lake. That made my 185 pounds feel like 1,212 pounds at the moment of impact, vs. the 583 pounds of 65 years earlier.

TruckTire
Size
Bed
Height
Top Rail
Height
Tool
Box
Body
Mass
Impact
Velocity
Deceleration
Time
G-Force
1950 Chev/GMC15"30"51"0"155 lb11.275 mphGrass 0.2sec2.76 / 583 lb
2013 RAM 4X417"32"53"7"185 lb12.128 mphAsphalt 0.1sec5.55 / 1212 lb

15

All this adds up to my suggestion that one should not jump out of the back of his or her truck past the age of 75 or so, particularly not onto a Home Depot asphalt parking lot. In this example, the result of landing flat-footed and falling backward to land on one’s ass and both palms with arms fully extended is this , requiring one of these, followed a few years later, by this and two of these

By: Jim
Written: February 10, 2023
Published: February 11, 2023
Revised: February 12, 2023
Reader feedback always appreciated
footnotes
footnotes
i “Dog House”, as it was then known
ii While it is not possible for a human to reach Terminal Velocity by jumping out of a truck in a Home Depot parking lot, I can attest to the fact that it feels “terminal” when you hit the pavement.
iii Ignoring wind resistance, the velocity is independent of weight.