The Traffic Accident Reconstruction Origin -ARnews-

Re: Codfficient of Friction of Grass

Andrew Rich (ASRich@csi.com)
Tue, 29 Sep 1998 17:40:39 -0400 (EDT)

I have done some skid testing on grass and have found that a drag sled will overestimate the true mu. The first set of tests I did measured the vehicle's speed with RADAR, and mu was calculated from the longest tire mark in the grass. With ABS, the average value was about .5. A second set of tests was run using the VC2000 accelerometer; here, also, the drag sled came in around .75 while the mu calculated by the length of the skid and reported by the VC was an average of .5. The grass, as I recall, was dry and about 4 inches in length. Both sets of tests were done with ABS. If you want, Email me and I can pull the file on my tests and give you some better details.

I also have some interesting photos of the tiremarks left by ABS in grass.
Andrew Rich
ASRich@csi.com

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