What they did before 4 wheel drive was available…. - Page 4 - Escape Trailer Owners Community

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Old 11-09-2013, 08:57 PM   #31
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So in conclusion:

1. Under the worst circumstances and when you need it the most a standard differential results in your vehicle having only one driving wheel. Traction differentials (Posi-trac, Track- loc etc.) and computer controlled traction systems were developed to supply power (hopefully) to both drive wheels under these circumstances.
2. Under regular conditions it is 2 wheel drive with a varying ratio of power going to each wheel depending upon conditions.
3. Both answers are correct depending upon your perspective or parameters.
4. All things being equal 4-wheel drive is superior to conventional all wheel drive systems.
5. All things being equal 4-wheel drive pick ups are really light in the rear and are likely inferior to conventional all wheel drive.
6. Variables like having the proper tires, driving skill, horsepower, clearance, terrain and traction systems does not make all things equal and will change the outcome.
7. A pickup, jeep or similar 4-wheel drive has a low range position in the transfer case which gives it a large advantage in deep mud or loose sand and going down a slippery slope in control.

Clear as mud?

Dave
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Old 11-10-2013, 03:26 PM   #32
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Nice summary, Dave.

My version, shamelessly copied from Dave's:
  • A conventional axle with an "open" differential is always 2 wheel drive with a varying ratio of power going to each wheel depending only upon wheel speeds.
  • Under the worst circumstances and when you need it the most a standard differential results in your vehicle being limited by the driving wheel with the least traction. Variations of differential design (Posi-trac, Track- loc etc.) and computer controlled traction systems were developed to transfer power to the slower-moving drive wheel (with more traction) under these circumstances. Some "torque vectoring" differential designs can even apply more torque to the faster-turning wheel if that is desired for conditions.
  • Modern 4WD or AWD systems distribute power between front and rear axles in many of the same ways as the differential of an axle does between left and right wheels.
  • Variables like having the proper tires, driving skill, horsepower, clearance, terrain and traction systems are of comparable or greater importance to the basic features such as 2WD versus 4WD.
  • Some 4-wheel drive systems - most often found on pickup trucks, some Jeeps, and more traditional SUVs - have a low range position in the transfer case. Such very low gearing (in the transfer case or otherwise) provides a large advantage in deep mud or loose sand and going down a slippery slope in control.

That performance in mud of that car in the antique video that started the discussion probably had a lot more to do with ground clearance than anything else. Hopefully you won't be that deep in mud when towing your Escape!
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Old 11-10-2013, 05:20 PM   #33
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Brian,

There are no absolutes in this e.g. "is always 2 wheel drive". There is only an absolute if you consider only torque and not power. It is power (HP) that is propelling the vehicle forward, not torque alone. If a wheel isn't turning there is no power going to it. 100% of the power can and will go to only one wheel under extreme conditions. Hence the conclusion by people that a conventional axle is or can be one wheel drive. They arrive at this conclusion from the practical but not pleasant experience of being good and truly stuck with one wheel merrily spinning. Again both views are correct.

If you had said is mainly, usually or mostly 2 wheel drive I would agree with you. If I can give you an example where one wheel can not rotate yet the vehicle is able to move with a conventional differential would you agree that sometimes a standard differential is one wheel drive?

In addition to greater clearance the big advantage antique cars had were skinny tires which often sunk down to firmer ground and didn't require nearly as much power.

Dave
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Old 11-10-2013, 05:36 PM   #34
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Is this still the Escape forum ?
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