The Traffic Accident Reconstruction Origin -ARnews-

Re: Pendulum Drag Tester

Ed Livesay (elivesay@alltel.net)
Sat, 5 Apr 1997 13:56:02 -0500 (EST)

The American Society for Testing and Materials (ASTM) also lists E707-90
which is entitled "Skid Resistance Measurements Using the North Carolina
State University Variable-Speed Friction Tester."

The paper's description goes on to read "The variable-speed Friction Tester (VST)
is a pendulum-type tester with a locked-wheel smooth rubber tire at its lower
end. A stream of water at a selected water test velocity is directed by a
nozzle along the specimen surface in the path of contact between the locked
pendulum tire and the specimen. The friction between the tire and the specimen
is measured from the energy lost in the pendulum. The tester is suitable
for field tests on pavement surfaces as well as laboratory use."

BUT; it also says "The values measured, VSN (variable speed number), represent
the frictional properties obtained with the apparatus and procedures stated
herein and DO NOT NECESSARILY AGREE OR CORRELATE DIRECTLY WITH THOSE OBTAINED
BY OTHER SKID-RESISTANCE MEASURING METHODS."...and "Uneven surfaces in the field
may provide inaccurate VSN measurements. Extreme care should be taken when
using the VST in the field."

Boy that shed some light... no wonder most of us haven't heard of this method
until it come up on this thread!
Ed Livesay
elivesay@alltel.net

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