FWD vs. AWD vs. RWD - long

["Belt, Stephen D" <stephen.d.belt@intel.com>]

Because I agree this matter was not settled when it was previously
discussed, and because I ignored the matter originally, I am now
offering the following information.  Please take this post as that:
information.  

In my opinion, this list should strive to have the properties espoused 
by www.fool.com:  Educate, Amuse, Enrich.  Persuasion should be 
unnecessary.  Give people information and then let them make their own 
decision.  If it differs from you, so be it.  It doesn't make them wrong 
or right, just different.

My official opinion on the matter is that neither FWD nor AWD nor RWD
is better than the other.  All have their merits and their weeknesses.
Each driver should consider these, and then based upon their own driving
style and environment, chose a drivetrain that suits them best.

Here in Phoenix we have long straight roads and horistorically we have 
had very few freeways (though that has recently began to improve). A 
curve in the road is rarely seen, except those found in residential 
areas.  As a result I have an affinity towards cars that go very fast 
from 0-60.  I don't care much about cornering and certainly nothing about 
snow/rain handling.  Not to say I didn't consider these aspects when I 
purchased the Jetta, but they didn't rank high up on the list.

Now, I'll explain what I think the merits and weaknesses of each
drivetrain are, and then what I think would be best for me personally.

FWD - merits:  

These cars offer a significant advantage in the area of cargo and 
passengar space over all RWD and AWD vehicles.  Without the "hump" 
in the middle of the car, passengers have more leg room and  without a 
rear axle, trunks are bigger.  This is undeniable, and is the primary 
reason FWD was pioneered.  A softer advantage over RWD is that FWD 
equipped cars (not all, but most) have more weight over the front 
wheels, and therefore benefit in lower traction settings where weight 
over the drive wheels is a benefit.

FWD - weaknesses:

These cars suffer from torque steer.  Its unavoidable.  Some cars
suffer only slightly (like the Type R), but all suffer to some degree.
These cars also have a larger weakness:  The drive wheels are always
pointed in the same direction as the steering wheels.  The power slide,
therefore is not possible.  Now, I've never put a car into a power
slide, but I've put my Suzuki Quadracer (4 wheel RWD ATV) into one 
many, many times.  Done properly and safely its the fastest way to
turn...plus its a lot of fun!

RWD - merits:

Basically, RWD cars don't have the FWD weaknesses.  There's no torque
stear and their's the ability to power slide.

RWD - weaknesses:

As suspected, the opposite of the FWD:  Less cargo capacity and typically
less traction.

One final note:  A lot has been written (possibly not here, but I've read
it a lot) about pushing vs. pulling a car around and that one is better
than the other.  Frankly I don't believe there's a conclusive argument
as to whether either push or pull better.

AWD - merits:

As expected, AWD offers the possibility of better traction than either
FWD or RWD.  AWD alone cannot overcome all traction problems, like ice, 
but in rain and snow AWD will provide more traction than either FWD or AWD.

AWD - weaknesses:

The biggest weakness is the loss of effective power caused by the added
rotating mass.  The motor must now spin 2 more wheels, a transfer case,
two extra axle shafts, and an extra differential.  All that rotating mass
has to be overcome by the motor and it isn't free.  On dry straight
pavement, the RWD and FWD vehicle will be faster (even if the trunk is
loaded with the weight equivalent to that of the extra AWD components).
Many have noted how a lightened flywheel increased throttle response.  
Well imagine bolting on a heavier flywheel...now you've got AWD.  This is
the primary reason AWD vehicles are not used in CART, INDY, F1, NASCAR,
and most other racing venues (including oddly enough SCORE desert off-road
racing, where Ivan Stewart races a RWD truck in the sandy desert).  
Maximum power and torque are needed on the pavement, and none of it can
be sacrificed for the benefit of traction.  In these settings, traction is
not the limiter, but rather either hp for top speed or torque for rapid
acceleration, or both (F1).

I want to point out one last mis-information that was posted.  Unless the
vehicle is equipped with a limited slipping or locking differential (I
don't know if the quattro does or not, but I suspect not), an AWD vehicle 
must have either both front or both rear wheels applying positive power to 
the ground to move.  I'm sure many of you saw the movie My Cousin Vinnie.  
I hope you recall the scene with the car stuck in the mud, one tire
spinning.  
If that vehicle were AWD and there was also limited traction in the front, 
such that either of the front tires could spin, the car would still be
stuck.  
You see, open differentials are a fickle things.  They send the maximum
power 
to the tire with the least resistance.  Thus if one front and one rear tire 
have no traction, an AWD vehicle will not move.  That's why I mentioned that

ice is still a difficult problem for an AWD vehicle (not that its any easier

for either a FWD or RWD one).  

Of course the solution is locking the differential.  With such a simple
solution, why is this never ever implemented?  Because in order for a
vehicle 
to turn, the inner radius wheel must spin at a different speed than the
outer 
radius wheel.  If the differential is locked, this is not possible.  Thus in

order for a locked vehicle to turn, there must be a loss of traction by 
either the inner or outer wheel so that they may both spiin the same speed, 
and still enable a turn.  This is possible on dirt/gravel/ice, but its
really 
hard on dry pavement.  As well, if you think torque steer is bad in the
Jetta, 
grab ahold of the wheel of a vehicle with a locked differential in the front

and try and turn.  Its like a wrestling match.  The vehicle wants
desperately
to travel in a perfectly straight line, and argues aggressively against any
attempt otherwise.

A know a thing or two in this space, because I have a Dodge Ram with a 
locking front differential and a limited slip rear.  I can lock the front 
on demand, at the press of a button.  I added the locking front, because the

limited slip did not solve the problem of being able to move forward when
one 
front and one rear wheel were completely suspended in the air.  In this 
setting, the limited slip was defeated and both suspended tires spun.  The 
same is possible on ice, though I've only been on ice once in my Ram.

So, which drivetrain is actually best for me:  Because I don't need the
traction benefits of AWD or FWD, don't want the power loss associated with
AWD, the loss of cargo space isn't terribly important in this vehicle (I 
have a full size Suburban and Dodge Ram for cargo), and because I prefer 
the handling characteristics of RWD, I think RWD would be best for me.
Is it the best for you?  Maybe, maybe not.  Can I tell you what's best for
you?  Definitely not.

Lastly, I know when I signed on I mentioned getting this vehicle as a 
project vehicle to turbo- or super-charge.  After driving it for one year,
I've decided my time horizon for this car has reduced from 5 yrs to 2 yrs. 
Its just too noisy and uncomfortable at freeway speeds.  In all likelihood 
a BMW 3-series is in my future...probably this time next year.  I'll drive
the S4 as well, and who knows.

Steve Belt - Scotts, AZ
1998 VW Jetta GLX