Quote: Originally posted by 4x4abc  |
In the previous post, I am agreeing with you (about the PR talking points).
On the one wheel drive vs 4WD or AWD, you don't know which one wheel will have traction, so power must be available to all four. Subaru claims that
their system will power that one. I don't know, and it didn't help my son (but, as I said before, I wasn't there and maybe there was something holding
him in place).
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understanding 4WD is not easy
it seems easy - but it isn't
here is the basic rule for all 4x4
they use up to 3 differentials to direct engine revolutions to the wheels
the amount of force (torque not power) reaching each wheel is ALWAYS equal
that's where even most 4x4 "experts" get it wrong
they tend to say "All power is lost at the wheel that is slipping"
#1 it is torque, not power that moves a wheel
#2 nothing in physics is ever lost
one of the weird characteristics of differentials is that the wheel with the least traction determines how much (equal) force the other wheel(s) get
since only a low amount of force is needed to make a wheel on slippery ground spin - the other wheels also get that same low amount of torque
4 times very little is still very little
often not enough to move the truck
what Subaru and all other vehicles with automatic traction control do is - they create a little bit of extra resistance at the slipping wheel -
increasing the amount of torque at the slipping wheel
that increases the amount of torque at the other wheels by the same amount
remember, torque is always equal at all 4 wheels
with the increased total amount of torque the car is likely to keep moving
what makes some trucks with automatic traction control better?
they create a higher amount of resistance at the slipping wheel(s)
netting a higher amount of force at all wheels
creating a better chance of moving
however, for serious off road use automatic traction control is severely limited
they work best on vehicles that are still moving
they don't work well on slow moving trucks or stuck trucks
for serious/professional 4x4 use a mechanism to disable the differential is needed
called diff locks or other fancy names.
if you are stuck in the jungle with a rental 4x4 (no diff lock) and the bad guys are shooting at you - take your diff cover off (forget the oil, it is
not need short term) - stick a piece of wood in between the diff gears - now you have a diff lock and can drive out to safety
diff locks require stronger, heavier, more expensive axles and diff gears
they have some serious draw backs (like all potent medicine) and require serious training
that's why you don't find them on most 4x4
and if they are often only in the rear
any feedback on which 4x4s have 3 diff locks?
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