This happened on Most Shocking once. A dude driving a stolen limo. I found the video.
They didn’t state the speed, but I doubt he was going much over 25 MPH
Is it rear-wheel steering that makes it unstable? I always figured it was an effect of the caster on the steered wheels.
When you turn the steering wheel back and forth, the front wheels pivot to the left and right. That pivot is not straight up-and-down, it’s angled slightly such that the axis of rotation intersects the ground ahead of the tire. Since the point of maximum drag is behind the point of rotation, it has a centering effect. Take your hands off the steering wheel and the forces on the tire will push it back to straight ahead, the same way the air pushes the fins of a dart behind its center of gravity.
Turn the car around and it’s a different matter. Steer the wheels a little bit off dead center and the caster angle will try to make them steer more in that direction. If you don’t catch it quickly, the steering will turn all the way left, or all the way right.
Try it with a shopping cart. Push it forward for a little while and the castering wheels will be rolling forwards. Then walk around to the front of the cart and push, and those wheels will quickly spin around the other way.
I’m not an engineer, but I’ve set up many a suspension. I always set the caster first to obtain the maximum positive setting. As you’ve said, caster is what makes the wheels want to straighten out, and negative caster would produce the opposite effect and the car would want to keep turning.
Some vehicles have implemented four wheel steering to reduce the turning radius, but they have to severely limit the rotation of the rear wheels because too much makes the vehicle difficult to drive. I think that some low speed vehicles, like zambonis, have successfully utilized rear steer. It’s also a topic of interest among bicycle geeks. I was very surprised to find that the Thrust SSC, which I believe still holds the land speed record at 763mph, is steered only by the rear wheels. Although that car has a very limited steering angle, if it isn’t causing a problem at that speed then I guess it’s feasible for the street.
I was also thinking of Buckminster Fuller’s Dymaxion car from the 1930’s, with two front wheels and one steerable rear wheel. According to that link, it reached 90 miles per hour (with a claimed top speed of 120). It also says that the rear-wheel steering made it difficult to drive.
The caster setting while driving in reverse won’t make it impossible to drive at speed just a lot more difficult.
I have driven cars for a distance at fairly high speed (1/4 mile or so at 20+mph)
It’s doable but requires concentration and small steering inputs. Did I mention concentration?
The drivers in that commercial EARNED every penny they got paid, that was an awesome piece of driving.
So how fast were they driving? Could they have shot the scenes at standard speed, then just speeded the playback up? (To give the illusion of speed)?
Many years ago I built a car just for racing in reverse. It was a demo derby car and one of the races at the monthly show was a 6 lap race in reverse. Other than the usual stuff to get the car ready, I also flipped the rear end over. That car (a 74 Chevy Caprice) was capable of doing 70 or more while going backwards but had a top speed of about 25 going forward. The only other thing I did to the car was disconnect the front brakes, having only the rear brakes work made slowing down for the corners much easier. I got my lap times to within a half second of other cars that were being driven forward on a quarter mile short track. The more experience backward drivers got even closer time wise.
Wouldn’t they just install a car “shell” backwards, making it look like the car is being driven in reverse, like they do in the movies?
I have extreme doubts that there was a second car there at all. Not only is it difficult to drive quickly in reverse, but the reversed car maintains a perfect gap with the forward car and always is going the same precise speed. I would be very surprised to hear that both cars were not CGI.
Without massive disclaimers on the ad, I highly doubt this. I know of one car company that got into a world of Hurt (multi million $ fine) for less.
I know a couple of people that do this type of driving. They are good. They make you and me look we should not be trusted with anything more powerful than a kids trike.