I am new not only to this forum, but to off-roading as well. I am trying to understand how 4WD systems work, what they do, and what I might need. In order to try to get to that point, I have looked at a lot of different webpages, talked to a lot of folks, and still have a lot of questions. Rather than asking a lot of really dumb questions, I thought I would write out what my current understanding of how 4WD systems work, particularly in regards to the 2005+ Tacoma. I would like to hear anyone thoughts on what I have right, what I've got wrong, and what I'm out to lunch on. Here it goes.
Thanks a lot.
A Newbie's view of a Toyota Tacoma's 4-wheel drive system
I have never owned a 4-wheel drive vehicle, or even a truck,
but I believe that the time has come for me do to so. Looking
at everything that is available, the truck that meets my needs
best is a Tacoma Double Cab.
In talking to friends and acquaintances about this choice, I
have learned many things, one of which is very few folks seem
to understand how a 4-wheel drive system works. Coming from
a point of view of "See one, do one, teach one", I have put
this note together to try to see if understand what is available
in a 2005+ Tacoma.
Tacomas come in PreRunner (2-wheel drive- 2WD) and a part-time
4-wheel drive (4WD) systems. 2WD is basically a rear-wheel drive
with a differential between the two wheels so that the wheel can
turn at different rates of speed, eliminating (or at least
reducing) the effect of axle/transmission windup (ATW).
4WD Tacomas seem to come in three flavors: Two, "standard" 2WD
differentials, Limited Slip rear differential and Locking Rear
differentials. No Tacomas come with a center differential for
all four wheels.
In a standard 4WD configuration, you are getting essentially
two 2WD systems. Both sets of axles have their own differentials,
which vary the speed of the wheels to avoid ATW. This sounds
great for tire, axle and transmission wear, but not good for
extra traction that folks want. However, this setup provides
more traction that a 2WD setup.
Now things get foggy...
In a Limited slip differential and
the Locking Rear differential setup, you get the same FRONT axle
setup as the "standard" 4WD setup: It's own differential that
varies the speeds of the wheels as needed. There are no stock
options for a Limited slip or Locking front differential.
In a Limited slip setup, the two rear wheels are somewhat
linked together, in that there is some relationship between the
rotational speed of both tires. Even if one wheel is completely
without traction, it will still spin at some (reduced) rate of
speed compared to the speed of the other wheel. This provides
somewhat more traction than a standard 2WD setup. I assume that
this is due to the fact that the traction of the tires is
constantly varying, so that if you get a momentary increase of
traction, you can take instant advantage of it, rather than
have to wait for the wheel to start to spin up in the base
In a Locked rear setup, the situation is such that when locked,
both rear wheel will spin at the exact same rate of speed. The
advantage of this, I guess, is something like "more of the above":
The more you spin, the more likely you are to take advantage
of momentary increases in traction. I assume that you would not
get a overall torque effects where the truck would spin the direction
that the slower moving wheel is. Both wheels are moving at the
same rate of speed, so when they grip, they grip (However, you might
still get this side to side movement since the two side could have
different traction amounts at the same time...) The disadvantage
of this is that you are prone to damage/issues with ATW if you drive your
locked setup on dry pavement.
In order to get the Limited slip (rear) differential, you need
to get the SR5 Package 3 (I think). In order to get the Locking
rear differential, you need to get the TRD Off-Road package.
Now, 4WD comes in two gearing modes: 4WD Hi and 4WD Lo. It seems
that this only has to do with changing the gearing of the
transmission, so that you move slowly ("crawl") and take advantage
of moving your peak torque (and HP) bands to lower speeds. This
is completely separate from the discussion of differential setup.
HOWEVER, Toyota apparently only offers a 4WD Lo gearing option
if you get the Locking Rear setup of the TRD package.
ABS is also standard equipment on this truck. However, Toyota
also offer a Vehicle Stability Control system. This system will
correct for understeer and oversteer by using independent brakes
on each wheel. Essentially, this sounds to me like ABS with
a faster processor and better programming, and sounds like a good
idea. This setup ONLY works in 2WD mode, which for me would be
fine since in most situations, on the road you are in 2WD mode.
In any 4WD mode, the VSC is automatically turned off. There is
no way to manually shut this off in 2WD.
I do not understand WHY Locking Rear differentials are so much
better than Limited Slip. I would think that the difference would
be incremental, not extraordinary. I would think that the vast
majority of driving I am going to do is to and from off-road
kind of places. My goal is not rock crawling. I want to be able
to take any road that goes from point A to point B without worrying
about it. For example, I want to be able to go up Schaffer Trail,
over Weston Pass, see if you can drive from Crested Butte to Marble,
take the "new" road from Goose Bay to Quebec, drive to McCarthy or
Not necessary go to find lots of mud, but get
through it if I have to. In some ways, I want the ultimate road
trip machine, and also have the ability to take stuff to the
dump and pick up 1/2 cord of wood.
From this, I would think I would want the 4WD model, with VSC (for
those really long drives on road), with a low gear range to get
over "tough" stuff. This would mean getting the TRD package.
(Unfortunately, this is most expensive option.)
Any thoughts on this? I really (REALLY) would appreciate any
feedback and corrections to my understanding on 4WD works.