h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Watching Mythbusters last night, the presenters were trying to prove or disprove the myth that The Hoff couldn't possibly have driven Kit (or have Kit drive itself) into the back of a moving lorry.

I'm sure you've all seen it, but basically Kit (at 55mph) drives up to the rear of an articulated lorry with its rear door down, dragging along as a ramp. Kit drives up the ramp and parks comfortably in the back of the lorry. The theory was, that as soon as the car hit the ramp, it would accelerate and therefore continue at some velocity before crashing spectacularly through the front wall of the rear container.

They proved, quite plausibly, that this would not be the case - ie 'Myth Confirmed'.

Apparently, the inertia of Kit (although travelling a few mph faster than the lorry) would equalise with the lorry at the point it hit the ramp, but with a noticeable immediate slowing of the front wheels. This explanation I could comprehend, but as often is the case, the science wasn't fully explained.

Would this have only been the case if Kit was a rear-wheel drive? What if it was front-wheel? Would the drive have continued at 55mph and accelerated the vehicle up the ramp? If it was rear-wheel, would breaking have been needed as soon as the rear wheels hit the ramp?

More importantly, what would have been the results if Kit was a 4WD with centre diff?

Layman's explanations please...

Ever seen The Italian job? They pull the same trick with three Minis driving onto a bus (seats removed, naturally). Minis are front-wheel drive and they did the stunt for real.

As for how it works, I think a certain amount of driving finesse is needed to lift off the throttle and apply the brakes at the right time, but the car has to go up the ramp, which will rob it of a certain amount of inertia. And have you ever tried starting off in fourth gear from stationary? You don't get much acceleration. Stalling on the way up the ramp may even be a danger.

no hoovers involved then?

No no...Night*rider* not...

n i g h t h o o v e r



...although I suppose n i g h t h o o v e r could reverse a lorry at the Hoff and Kit and achieve the same end result

t

I don't see a particular problem with this. All you really need is for the car to be going a bit faster than the lorry, and the driver to cut power just before it hits the ramps. Kitt was a Transam IIRC, so definitely rear-wheel drive, so all the driver would have to do was cut the power when the front wheels hit the ramp, and then brake gently after the rear wheels hit. Good driving certainly, but by no means impossible. Landing a plane on a moving aircraft carrier is probably much harder.

Remember that the car is cruising at this point - it's not as if it's at full power and would suddenly accelerate on hitting the ramp. Even if the driver kept the power on the sudden deceleration on the driving wheels would probably just stall the engine. As Kitt was fully intelligent, I'm damn sure he had ABS and traction control (even my humble Golf has) which would make it even easier.

I too heard that they did the stunt for real with front wheel drive minis.

OK Dave, I more-or-less understand what you are saying.

What, then, would happen with a centre diff? Given that (as I understand) most can't handle anything more than 10mph differential between front and rear drive, would it fail catastrophically as the front wheels stall and the rear wheels continue at 55mph?

And cripes! Of course, it was KITT...

Thinking about this, yes you'd probably break the diff.

With a normal diff, it wouldn't be the speed differential that did it Huge speed differentials happens all the time, through wheelspin or going over a pothole when one wheel leaves the ground. A limited slip diff would make things worse, but I think it'd be the sudden deceleration on one side of it that would do the damage.

What about Kitt leaving the truck, though? Would that be possible?
The problem I see is that the truck is going forward at 55 mph, while Kitt is actually going backward at whatever speed. Wouldn't this kind of treatment be really hard on Kitt's tires? Kitt's wheel suspension?

Y.

Think about an aircraft landing for this one. The wheels are not revolving, yet the plane is doing a hundred miles an hour plus... You see the puff of smoke as it hits the ground, but then they soon spin up to speed.

The important thing with both going onto the truck, and leaving it would be to have the clutch pressed, so the wheels can spin.

If you ever watch the Italian Job, one of the Minis was going full pelt at the ramp, but caught it wrong, and the wheel stopped instantly, then the car rolled backwards - both showing that the clutch was pressed. At the moment when the car successfully enters the ramp, there is only a few miles per hour differece between truck and car, so while driving up the ramp you just need to have suffiecient speed to coast up, or be ready to change into low gear quickly.

How KITT did this with an automatic box is another question.

Oh, and saddo that I am - it's 2 T's in KITT, for Knight Industries Two Thousand... sorry!