Would an all-wheel drive vehicle behavior any differently when driving into the back of a big rig at speed? In the 2-wheel drive shown in the episode, once the car hit the ramp it slowed down. However, in an all-wheel drive vehicle, the rear wheels will still be pushing it at 55mph. Correct? Wouldn't this change things?

Actually, if I'm not mistaken that's an 80's Camaro, those cars were not front wheel drive, they are rear wheel drive, so they are pushing.

yathe camaro and firebird are rear wheel drive.. i dont know much about 4wheel drive vehicle but as long as the front and rear wheels can spin at different speeds it would be the same results

The whole point here is that there's no real difference between doing this at 55 mph as there is at 0. (Other than lining up etc) It's all about relativity.

But first I'm going to make clear the situation I'm setting.
Both vehicles start at the same speed.
The car then accerelates up the ramp.

Lets do 0 first. Both vehicles start at 0 and the car accerealtes to 5 mph up the ramp. The relative speed of the car is 5 mph.

At 55 the car acceraltes to 60 mph up the ramp. The relative speed is still 5 mph (60-55) so the car is moving only 5 mph in relation to the system, even though the system is moving at 55 mph.

The only way the car is going to shot up the ramp is if the truck suddenly stops. Lets say the truck decerlates to 35 and the car is doing 60 the car will shot up the ramp at a relative speed of 25.

orcan-

i understand all that, but in the case of an AWD vehicle, would it still work the same?

wouldnt the rear tires be spinning at 55 mph while the front tires would be going <5 mph? i know AWD cars have center differentials but that is a huge difference between front/rear wheel speeds...

I think that the key here is that the front and rear differentials in a four-wheel drive car allow the left and right wheels in each pair to turn at different speeds but still distribute all of the power evenly between the front and back. I think this would turn out badly for the driver and the truck, because you would have the car trying to give equal power delivery between a surface that is not moving much at all relative to the car (the road) and a surface which is moving at 55 mph relative to the car (the ramp).

This seems like it would defintely cause the car to lurch forward up the ramp. I don't think it would be catastrophic though, because the wheels would probably slip for a while and it still takes several seconds for a Camaro to accelerate to a speed that it could not be stopped before reaching the interior wall of the truck. All the driver would have to do would be to let off the gas and he would be okay.

It does seem like a front wheel drive car would have this problem as well.

The safest plan overall seems to switch into netural just as you hit the ramp.

I think there is some confusion between the terms all-wheel drive, and four-wheel drive, which are used here. All-wheel drive vehicle, as stated, have a center differential, which would allow the front and rear wheels to operate at different speeds (even the 5 & 50 mph speeds stated).
Four-wheel drive has no center differential so the front and rears always spin at the same speed, and unless one of the pairs of wheels started to spin against their respective surface as the front wheels hit the ramp, there would most likely be a dramatic failure in the driveline, be it transfer case, u-joints, axles, whatever. Not to mention the extreme possibility of a loss of vehicle control.

I'm a little curious about a Manual transmission vs. an Automatic. I'm guessing the Camaro they tried it out with was Automatic, thus the car handled it fine. I could see a problem with a Manual transmission in that the car may stall when the drive wheels hit the ramp. Lets say you are in 5th gear going 55mph, and then hit the ramp. Your tires slip some (as seen on the high speed footage) but eventually they grab and want to move ~5mph. Trying to move the car at 5mph while still in 5th gear could easily create a stall situation. You could time it up right and shift down the moment it hits, but what if you don't? I think you could easily stall the car out.

to iobus55 : having both owned an 80's camaro and also experienced in using a manual transmition, in a lot of cars, the 2nd gear can take a car up to 80 or so in an automatic (or at least my cars have...), not always so much with a manual. so I geuse my point is that an experienced driver would only be in 2nd or at most 3rd, but most likely 2nd (god help 'em). The best thing to do is downshift before reaching the ramp. If the car is in 2nd it will not have any problem after it hits the ramp: the rpm will drop and the engine will chug up the car the rest of the way up *so long as it runs well. Lemme know what you think . oh yea, 4th and 5th gear would cause badness to happen, but all you'd need to do is push the brake and resart the car and put it in 1st while you're still chillin on the ramp.

"i understand all that, but in the case of an AWD vehicle, would it still work the same?"

Orcan's point was that it doesn't matter in the slightest. This was an absurd "myth" to test, as the attempted explanation at the beginning doesn't make the slightest bit of sense, their small-scale test was awful, and the new explanation about intertia was barely coherent.

There was never any reason to expect a change in velocity relative to the road. Period.

Now, if you had a really long truck with a car in it, and started the truck moving at 60, could you get the car up to 120 (with the speedometer at 60)? Yes. But that requires acceleration, which doesn't magically happen just by driving on to something moving at the same speed you are.

The fictional Knight Rider car, KITT, could switch to 4-wheel drive when needed. There was an episode where they needed to go off road, so Michael pushed a button and KITT switched to 4-wheel drive and traction spikes came out of the tires.

It's kind of funny to me that this was ever considered a myth, because in the Knight Rider show they actually drove KITT into the back of a truck in nearly every episode (though maybe not as fast as 55 mph). This show was made for TV in the 80's, so they didn't use computer graphics, but instead either used models or did the stunts for real. When they did use models it was pretty obvious, and they didn't use models when getting in and out of the truck.

there were as far as i know two or three episodes where kitt had too go off road on was through the off road rase we call baha the second one i remember was a moto cross race and both michael and kitt agreed too the fact that they did not like it very much but do remember one episode where the spiked tires needed too get up a very steep incline on a hill

The myth is CONFIRMED!!, It was about could the Knight rider drive into the truck & not crash into the front of the trailer. They did it with a vehicle simular to Kitt. & it worked, I think they were amazed that it worked, but it did.
Retesting this with 4 wheel drives, all wheel drives, front wheel drives, sherman tanks bicycles, segways, rollerskates, tricycles, scooters or whatever doesn't seem necessary.

as orca nsays, the relative speed between the vehicles might be 5 mph, however, the relative tangencial velocity of the wheels against the road is not the same against the platform, so it could acually work, you could might have a sudden acceleration with a AWD, i think it's be interesting to see.

Just to add one thing regarding auto vs manual tranny. This was done in the 70's in a movie called Gumball Ralley with a Ferrari (type?). Surley it had a stick in it so as far as stalling at the threshold of speed transfer, I'm thinking they depressed the clutch and rolled it in like they do in a garage at home.
xs

Did anybody notice how Jamie almost dropped the tranny when he backed the car off the ramp. Looks like he had it in gear when he backed it off...

The reason you could do this with an AWD car is because AWD systems have a (in addition to a front and rear differential)center differential that allows the front wheels to spin at a different rate as the rear wheels. The front / rear differential on a AWD car like the differential in the rear of a RWD car or inside the transaxel of a FWD car allow the drive wheels on either SIDE of the car (not front to back) to spin at different rates, because when you are turning the wheel on the outside of the turn is spinning faster than the inside one because it is "drawing" a larger circle. The important thing is with AWD that both front and rear wheels are still turning FORWARD, regardless of the difference of speed. HOWEVER the differential might fail (dramatically) if the difference in wheel speed is great enough, depending on how beefy the diff was designed. In a conventional differential (including limited slip and posi traction) When one side of the differential spins WAY faster than the other, the pinion gears friction weld to the pinion shaft and seize, and something fails. This may not be the case with a torque sensing AKA torsen AKA quafie AKA torque biasing, you maybe able to get away with it, but they are generally 4-5 times the cost of a comparable conventional unit. A "locked" diff would either break itself or or the axle shafts, or both (which ever is weaker). I don't think any one runs a locked center differential in an AWD car unless they exclusively drag race.

IMHO doing this with a FWD car, while mathematically possible, would be a failure. Simply because hitting the ramp would be equivalent to holding the RPM at 3000 RPM in N and dropping it into gear. And while a nice beefy RWD trans might take that for a while, most compact FWD trans axles will likely fail. either the input/output shafts or drive chain would be the most likely failure. It might be possible to take some speed at the ramp and then go into N and coast up it... but I doubt you could take enough speed at the ramp and still line up perfectly, you would need a wider ramp.

No matter how many wheel drive, when it goes up the ramp, the only inertia availible to "speed the car up the ramp" is in the drivetrain. The wheels and drivetrain don't have enough inertia to accelerate the car.

In the 2nd test, you can see the rear wheels spinning because of the wet ramp and drive train inertia but it's not enough to accelerate the car any appreciable speed.

Compare the momentum/inertia of the drive train to the whole car, and you get an idea of why it won't just jump up the ramp like some people seem to think.

Stunt drivers consider this to be the most dangerous stunt they are called upon to perform.

[quote]Stunt drivers consider this to be the most dangerous stunt they are called upon to perform.[/quote]

?? They did it on Fear-Factor with the (non-stuntman) driver blindfolded and being verbally guided by the (non-stuntman) passenger
... using RWD Camaros.

PS- Cars with electronic traction control or stability programming would go nuts if you tried this.