CarGuy250, I agree with all of the above replies. You didn't mention what
application (Street driving? Road racing? Drag strip? Airport runway? Bonneville?)
you have in mind. Here are some things to think about:
For street use, using sticky and large-enough tires should give you all the traction
you need for all 4 tires. But using airflow could help. If this is provided by motor(s)
or engine(s), it adds a significant amount of weight and cost. And controlling/adjusting
the amount of this pumped air could be quite challenging. If the airflow is automatically
provided by your forward motion, the effect of this airflow will vary a LOT, based on
your speed. At relatively low speeds, you won't notice much difference.
At higher speeds you will, but achieving this will require more horsepower to push
the vehicle. Do you have this power available?
For road racing, the same applies.
Drag racing is mainly about acceleration. You could refer to what others have
done to succeed. Unless you are going REALLY fast, you could probably benefit
more from shaving weight and using sticky tires and a smooth overall vehicle
shape, compared to the power-hungry aero tricks (such as "wings", "spoilers",
"flaps", etc.). And using suction, provided by motor(s) or engine(s) adds a lot
of weight. Not likely to provide a net benefit.
On an airport runway, which already provides good traction, you won't have as much
distance available for acceleration. So mass won't be your friend there. This
suggests that you don't use suction provided by motor(s) or engine(s). Downforce
provided by aero could help if your vehicle is powerful enough to need this. Many
top fuel dragsters have more power than they can put to the ground unless they
use the spoilers to create aero downforce. And this applies to funny cars as
well. But they all have available horsepower to use for the aero downforce.
At Bonneville and other dry lake events, you have a long distance in which to
accelerate. So the mass of your vehicle is not the only important factor. It may
(based on the weight on your drive wheels) actually help by increasing traction,
thereby providing better acceleration.
Many, many vehicles have so much power available to the drive wheels that
spinning those wheels becomes a HUGE issue. Not only because spinning them
limits forward acceleration, but perhaps more importantly (especially from a
SAFETY and CONTROL viewpoint), spinning wheels don't do a good job of
keeping a vehicle aimed where you want it to go. Spinning rear wheels have
a tendency to push the rear of a vehicle sideways and forward at the same
time. This causes the vehicle to get sideways, frequently causing it to roll.
This should be prevented/avoided as if your life depends on it, as it well might!
Generally, I suggest that you err on the side of caution, and make only small
changes at a time, gradually improving the results when these small changes
are successful. Safety first! And good luck to you.
My suggestion is to keep the aerodynamic shape of your vehicle as smooth
as you can. And make as much (dependable!) horsepower as you can. Then
take any necessary steps to get it all to the ground. The methods for this
are likely to depend on things like your budget, the class of your vehicle
(in competition).
Good luck, and welcome to the discussion.