AWD Performance, ad infinitum...

[AUDIDUDI@delphi.com]

While doing some research on another matter, I came across the following in
the second edition (published in 1986) of Paul Van Valkenburgh's book "Race
Car Engineering & Mechanics":

"With current race car power, weight, and tires, these mathematical
predictions indicate that on dry pavement four-wheel drive is negligibly
faster in a steady-state turn.  And although it does accelerate a car out of
the turn much faster in low-speed corners, the effect diminishes rapidly at
higher cornering speeds.  Above wheelspin speed in the straightaway,
however, the added weight of the front-drive mechanism is a definite
disadvantage.  Since most passing is done toward the end of the straightaway,
four-wheel drive would have to produce a very strong advantage in cornering
acceleration.  It also adds work to be done by the brakes and has a
complexity which affects reliability.  With the unknown development
requirements and unfamiliar handling characteristics, it may be some time
before it becomes popular in road or track racing.

"The fact that 4WD is currently doing very well under low-traction
conditions such as rallying however, indicates that it may not be long
before someone tries it in roadracing again.  It has certainly become very
popular on the street, especially as a relatively inexpensive addition to
front-wheel drive cars, even though the typical driver may not really need
it more than a few times a year.  As the analysis above [not quoted here due
to its length] showed, more important than its ability to pull out of the
occasional low-traction crisis, is its value in stability during sudden
surprises, where practice isn't possible -- such as rallying."  

Van Valkenburgh, for those who haven't heard of him, was the GM engineer who
helped design/tune the Chapparal Can-Am back in the late '60s and is thought
by many to be one of the great engineers/designers of all time.  His book is
required reading for anyone interested in the nuts-and-bolts of racing cars.

I think these two paragraphs neatly summarize why there can be no definitive
conclusion as to whether AWD is superior to FWD or RWD ... it depends on the
specific application you have in mind when evaluating it -- street or racing
-- the demands of which are completely different from each other.  QED. 

     _             _             
    / l       l o l  \       l o   Jeffrey Goggin
   /__l l l / l l l  l l l / l l   AudiDudi@delphi.com
  /   l l_l \_l l l__/ l_l \_l l   http://people.delphi.com/AudiDudi