Mythbusters “Big Rig Myths” Episode

Myth: You can drive into the back of a moving big rig, just like in Knight Rider.

The main fear is that if you are driving at speed, as soon as you hit the ramp of the truck, you continue to drive at speed through the trailer of the truck.

Full-scale test

With a rollcage, 5-point safety harness, and a helmet to protect him, Adam took on the task of driving a car into the trailer of a big rig. As Adam and stunt driver Mike Ryan drove along side to observe and coach, Adam attempted the test at 35mph and 55mph:

35mph: Adam had no trouble rolling up into the big rig trailer. As his wheels hit the ramp, they slowed down and allowed the car to ease into the trailer.
55mph: with rain everywhere, Adam still had no trouble parking the car in the big rig.
backwards: Jamie took over and backed the car out of the trailer

confirmed

Drafting a Big Rig

Myth: Drafting a big rig saves fuel

They emphasized again and again how dangerous drafting a big rig is: ~3/4 of truck/car accidents are caused by person driving the car and you’re driving in the blind spot of the truck. 150ft is minimum recommended following distance at 55mph, so even the 100ft test is considered dangerous.

Small-scale test

NASA let them do a small scale test to study the aerodynamics of a big rig. They captured video of smoke travelling over a minature big rig and verified that there is a low pressure area behind. They then stuck a minature car to a force gauge to study the difference with and without drafting.

7 car lengths: 21% drag reduction
10ft: 60%
6ft: 80%
2ft: 93%

Full-scale test

Freightliner lent the MythBusters one of their new Cascadia big rigs, which they are billing as the most aerodynamic big rig on the market.

Mike Ryan, Hollywood stunt driver, was there to educate Grant on the ins and outs of drafting. Also on-hand was Andrew Smith, test engineer, who helped them hook up a computer to the fuel injection system to accurately measure the fuel consumption.

55mph control: 32mpg
100ft: 35.5mpg, 11% improvement
50ft: 38.5mpg, 20%
20ft: 40.5mpg, 27%
10ft: 44.5mpg, 39%
2ft: 41mpg, 29%

The fuel economy actually dropped at 2ft. Andrew Smith’s theory was that at 2ft, Grant got nervous with the throttle as it was difficult to maintain that 2ft gap.

confirmed