The Traffic Accident Reconstruction Origin -ARnews-

Re: Snowmobile speed response to archive thread

Charles J. Berg ([email protected])
Fri, 6 Nov 1998 21:55:09 -0500 (EST)

Gentlemen,
As the original author of the article in question I feel a response is in order. I think you all missed the point!!
The point I was trying to make originally was that we had to add the length of the track to come up with an accurate speed. We all know that the back of the track falls. This happens for all the reasons you each have mentioned but simple gravity seems to be just as good an answer since the front boggies are physically held up and not allowed to drop while the rear boggies are allowed to drop a distance worked out by the designers of the snowmobile in question. Pick up the front or rear of a snowmobile and see it this is not true.

The real question is why we must ADD the distance of the track since we all know that we must subtract half the wheel base of a falling vehicle to have the speed come out accurate or as near as we can reasonably be expected to get it because of the different moments of inertia. With a snowmobile we have a unique vehicle in that the front(tracks) and the rear(boggie system) do not seem to follow the same laws as an automobile. This may be, in fact, because of the different moments of inertia on each system(i.e. front tracks and rear boggies). This is also vastly different than my Harley Davidson which for argument sake has a front and rear tire and suspension system with the engine and transmission basically centered(I know this is not actually so). Here again, however, we subtract half the wheel base to come up with a speed.

I appreciate all of your responses and am not in a position to argue with any of them. My intent was to merely make anyone who takes care of snowmobile accidents involving skid marks(?) to be aware of this phenomenon.
Charles J. Berg
[email protected]

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