The 1 million pound stunt
Last month, Ford released a video showing its new electric F150 pulling a bunch of train carriages with more F150s loaded inside weighing over 1 million pounds! What does it it mean? How is this possible? We know most 4×4’s are only able to tow more of less their own weight due to the limit of traction provided by the tires.
A gas powered F150 weights between 6100 to 7050 lbs and has a towing capacity of 5000-7000 lbs. (possible to hit 13,000 lbs with a distribution hitch but we will get to that later)
The 250,000 pounds stunt
Back in March, our fearless leader Elon Musk performed a similar stunt, albeit in a more subdued way. His humble brag tweet showed a Tesla X pulling 250,000 lbs of cargo out of a boring company tunnel.
The official weight of a Model X is between 5183 to 5531 lbs, and it’s official towing capacity is 4980 lbs.
Understanding what towing capacity means
So first is dead weight, the usual number we speak of, aka weight carrying tow capacity. This means attaching a trailer to a hitch behind the truck. Part of the cargo weight is carried by the truck’s rear axle. A truck can usually pull equal amount of dead weight as itself.
However, each vehicle usually has a second, usually higher weight capacity called towing weight, aka weight distribution towing capacity. Using a weight distribution hitch, the weight is more even distributed to all axles as well as the trailer, and resulting in 2x and sometimes 3x towing capacity as seen in goose neck and 5th wheel hitch applications.
Generally, the less cargo weight a vehicle has to carry, the more it can tow. In the case the F150 and Teslas scenarios, 0% of the cargo weight is carries by the vehicle and this is the free weight tow. We can expect a much higher tow rating in a free weight situation as opposed to if the trains were attached and resting on a trailer hitch.
But what about Elon’s pickup towing 300,000 lbs?
Few month ago, Elon tweeted that the upcoming Tesla made pickup will be able to 300,000 lbs or 150 tons. Now we are no towing expert, but the logical explanation is that Elon is referring to free weight towing. Otherwise it implies that a pick up truck can handle 75 tons on its rear axle (dead tow) or 50 tons on each of its axles in a distributed tow.
Of course there is this one time the Volvo claims one of it’s trucks can tow 750 tons that we shall not get into ?
Back to the Train – It’s actually really easy
Turn’s out both the F150 and Boring dirt cart stunt are quite easy to pull off because 1) the load is free weight towed and 2) rail tracks have super low friction coefficient. Road and Track Magazine breaks down the science in pretty simple terms where basically any pickup trucks could have done this pretty much.
Let’s imagine we have a 100-pound rubber ball sitting in a pile of loose sand. Say the coefficient of rolling resistance is 0.3. If we tie a string to that ball, it would take a 30-pound force to move it (F = Crr*N = 0.3*100 = 30 lbf). Now if we take that same ball and place it on concrete—a much firmer surface—suddenly our coefficient of rolling resistance decreases to about 0.01.
This adds up to an extremely low coefficient of rolling resistance—about 0.0015. To pull a 10,000-pound train across a level surface, you only need a 15-pound force. For a truck to move a 1.25-million-pound train, it only requires about 1875 pounds of force.
So there you have it folks! Next time you are looking for a challenge, push the limit of science and see how many heavy objects you can haul by placing them on tracks. Or even better, check out one of our escape rooms incorporating the latest in future technology and make science work for you!