AWD und FWD

["Al Powell" <apowell@agcom.tamu.edu>]

Randall M. said:

> .....Scott and I were debating
> whether one could show an advantage of AWD over RWD/FWD on dry
> pavement.  I say to do that on must have _one_ car that can be
> modified to be all three.  If you cannot do that then there is no
> valid comparison between them. 

This make me stop a minute and think.  Randall, consider this - IMO, 
a car should be optimally designed for the drive system which it 
*has*.  F/R weight balance, placement of driveshafts and fuel tank, 
exhaust system, and many other variables must be taken into account.

So I suggest that your comment about using ONE car is not necessarily 
correct.  A car which is designed for FWD will have inherent weight 
and design characteristics because it WAS designed for FWD.  Same for 
RWD.  I don't think you CAN use a single vehicle as a base 
for comparisons.

Actually, I don't think you can reach a valid conclusion by 
using any production vehicle as a basis for this discussion.

Now, if you want to posit a THEORETICAL or EXPERIMENTAL car 
which doesn't have to live in the real world with passengers, cargo, 
soccer-mom trips, etc., I would accept the premise that THIS vehicle 
would be a possible test-bed for more than one drive system: FWD, RWD 
and AWD.  However, to test realistically, you would have to alter the 
static weight bias, braking system bias, and other characteristics as 
you changed drive configurations.  What one would end up with might 
be the best System A vs. B vs. C that an engineer could design, and 
that might be the most realistic way to prove this point.  (Of 
course, we totally leave out driver skill, a critically important 
factor.)

I further suggest the results would be specific to the driving 
surface.  Asphalt?  Mud bog?  Mountains? Track?

I think such test-bed cars actually exist in racing circles.  Many of 
the more exotic cars are designed at the limit their engineers think 
is possible for drive system (and engine placement ) A vs. B. vs. 
other options.  They can choose any layout they like.  On the track, 
it would appear that RWD is preferred to FWD or AWD.  In rally 
circles and crossing mud bogs, it appears that AWD is preferred, or 
at least I believe that Audi carries a weight penalty for using it - 
which indicates it's an advantage.  I'm not sure that FWD has become 
a preferable format in any race application - but I'm sure someone 
will remind me of one.  

In consumer cars, FWD has become a favorite format for reasons of 
weight reduction, fuel economy, and reducing vehicle size.  It also 
provides a traction bonus for average-skill drivers in reduced 
traction situations.

That's the way I see it work out.  No one solution is best for 
everything.

Cheers to all.....


*.......................................................*
Al Powell, Ph.D.                 Voice:  409/845-2807
107 Reed McDonald Bldg.          Fax:    409/862-1202
College Station, TX 77843      
Http://agcomwww.tamu.edu/agcom/satellit/alpage.htm
*.......................................................*