Re: AWD performance

[dmiller@iea.com (Doug Miller)]

trishab@interwebb.com wrote:

>Eric is right......the more power you can put to the ground the faster
>you will exit the corner.  If you are putting your power to the ground
>in four places.....well, damn, you'll get it down with less HP....

I know I'm beating a dead horse here, but getting your power to the ground
in four places does NOT reduce the amount of horsepower needed, it simply
makes it less likely the available horsepower will overpower the available
traction.

>A good indication of this is to go to Mt. Washington.....watch the
>Mitsubishi's and Talons run the hill.  The AWD vehicles are definately
>faster.....gee, that explains why they run a class
>higher.......Hmm.....and if my understanding of Eric's racing experience
>is correct, he's driven much in the way of FWD vs. RWD vs. AWD.....I
>think he can safely say he has a command of the knowledge of what the
>cars will do.
>
>BTW, Eric, what HAVE you raced and you never mentioned if you raced with
>Willie Lewis or not.
>
>TTYL---Trish


The simple answer to the question of whether AWD improves dry performance
is yes. Not for all conditions, but overall yes.  I have never raced, but I
have been a Product Planner in the auto industry for almost 10 years, and
happily volunteered to work on an AWD assessment team at one point.  In
this capacity, I put in a lot of track time, and the AWD project was itself
a track-based effort using all manner of sophisticated force/weight and
speed measurement devices buried in the track itself. While there are some
tradeoffs (added weight, complexity, and internal friction), the dividends
of added traction are clear and measurable on the seat of your pants and
the clock.

On a race track, I can see where the advantage narrows as a well balanced
RWD car is using its rear contact patches to accelerate, and its fronts to
brake and initiate turns (broadly speaking, of course).  The track surface
is also fairly smooth, reducing the number of times the vehicle will have
dramatic suspension inputs that cause spinning (or spins) when the driven
wheels suddenly break loose as reduced tire downforce commensurately
reduces available traction. With huge rubber so grippy the rear contact
patches can handle most of the power most of the time, great performance
results. By contrast, a front drive car is using its front contact patches
to do all three jobs while the rears simply trail along. This setup is
horribly unbalanced without serious suspension work that only partly solves
the problem. Front wheel drive isn't even in the ballpark.

An AWD car is using all four wheels to transmit available power to the
track, nicely distributing the load.  The AWD driver can, in some
situations, get more power down without breaking a tire loose - such as
exiting a slow turn. But the differences would be fairly minor. Of course
in a race, minor differences mean victory when they can be duplicated lap
after lap. If two identically powered and setup cars weighed the same, and
one was RWD while the other was AWD, I think it would be hard to argue the
RWD car would prevail.  The trouble is, they wouldn't be set up the same
(diff tire sizes/weight distributions/spring rates would be required for
each to get the most out of their particular layout) and a direct
comparison would be impossible. Just have to go out and run 'em....

Put these cars on a public street, and the differences widen as uneven
surfaces and gravel patches intrude to severely impact the RWD car's
ability to get power down. Huge suspension inputs will dramatically impact
the RWD's vehicle dynamics, while they will be muted with all four patches
pulling.

What say you?

Doug Miller
dmiller@iea.com