Ordinary pavement in contact with rubber tires give a coefficient of
friction of about 1. There is no getting around this. It limits the
acceleration to about 1 g, which translates to a 0 to 60 mph time of
about 2.7 to 2.8 seconds. To quote the BMW owners manual on the subject
of traction control: "The laws of physics cannot be repealed".
On the drag strip, they coat the surface with TrackBite. It is
essentially contact cement. With a TrackBite coated surface, you can get
a coefficient of friction of 3, or perhaps a little greater. Thus, on
the drag strip, you can accelerate with 3 g's and get a 0 to 60 mph time
that is significantly less than one second.
The "layer of fresh rubber" helps, but that alone won't get you anywhere
near the traction that TrackBite will. A properly prepped drag strip has
maximum traction without any tires rolling on it.
There are several reasons that dragsters smoke their tires:
1) It heats the tire compound, and make it adhere to the prepped track
surface.
2) It removes a thin layer of aged hard rubber, and reveals fresh soft
sticky rubber.
3) It heats the track (slightly). This is of little consequence these
days. They have cooling coils under the track in the best drag strips to
hold the track surface at the ideal temperature.
4) It creates a spectacle for the crowd.
I should note that there are other tricks that drag racers use to help
get traction. They use the rotational inertia of the vehicle to "plant"
the rear tires during the launch sequence. They use the thrust of the
upwardly pointed exhaust to give down force. Further down the track,
they use wings. etc. to give many times the vehicle weight in down force
to help traction.
Bill D.
On 2/11/2016 9:30 AM, Jack Wendel wrote:
I though I heard of sub 3 second time reported, not theorized.
I recently read of a car that does 0 - 60 in 2.2 seconds. Tesla is FAR
from optimum.
I have never gotten an explanation I could understand of how
C_friction can
exceed 1 as I have heard regarding dragsters.
I'm not sure why you would assume 1.0 is the mas coefficient of
friction possible. Just aluminum to aluminum can be as high as 1.35.
Friction Coefficients for some Common Materials and Materials
Combinations
Materials and Material Combinations Static Frictional Coefficient
- /μ_s -_
/
Clean and Dry Surfaces Lubricated and Greasy Surfaces
Aluminum Aluminum 1.05 - 1.35 0.3
http://www.engineeringtoolbox.com/friction-coefficients-d_778.html
<http://www.engineeringtoolbox.com/friction-coefficients-d_778.html>
The reason high horsepower drag cars can get a high coefficient of
friction is because they put down fresh hot rubber on the track during
their burnout (it's not just for show, it is required). They then back
up and line the car up with those fresh rubber tracks. This results in
hot sticky rubber to hot sticky rubber contact which results in a very
coefficient of friction. That additional traction advantage continues
down the entire pass, not just at the starting line.
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20160211/acd8ee04/attachment.htm>
_______________________________________________
UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
http://lists.evdl.org/listinfo.cgi/ev-evdl.org
Read EVAngel's EV News at http://evdl.org/evln/
Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
