EDR DeltaV - The Effects of Tire Friction

Decided this might be a good time to add a specific topic on Electronic Data Recorders (EDR) and/or Crash Data Recorders (CDR)
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MSI
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EDR DeltaV - The Effects of Tire Friction

Post by MSI »

In the most recent Collision Magazine, Volume 16, Issue 1,
There is an article by Vandiver & Anderson entitled
  • Event Data Recorder DeltaV: The effect of Tire Friction
  • which includes
    • "In many EDR reports, the pre-crash deceleration from the bullet vehicle's braking is evident in its pre-crash data. For frontal impacts, the occupant kinematics would only produce greater driver braking, so it is fur co expect similar or greater braking during the impact. For a typical collision duration of 1110th of a second, and with a coefficient of friction or drag factor of 0.75, the /J.V from tire friction is the same as the speed change from skidding over a tenth of second which can be calculated as, 0. 75 * 32.2 fr/sec2* 0.1 sec * 3600 sec/hour/(5280 feet/mile) = 12/2 mph.

      While a I½ mph DeltaV might seem insignificant for the analysis of many collisions, in low speed impacts, and situations where there is a large weight difference between the vehicles."
We also have a forum topic from July 2020 on the subject:
  • In collisions why does Mass1DeltaV1 not always equal Mass2DeltaV2?
    which includes:
    In A Hurry Executive Summary:
    • Q: So why do we not always get M1*DeltaV1 = M2*DeltaV2 with msmac3D (and/or comparing EDR data for two collision partners)?
      • A: Why? Because of External Forces!
        • aka tire forces and other external forces (structures scraping)!
        Many of you evaluating collision with one or both vehicles having an EDR may have noticed this phenomenon affecting each vehicle particularly when braking is indicated in one or both vehicles.
        • We have often said
          • "The collision between two vehicles is not the same as a collision between two pool balls. More like two crushable rectangular boxes with wheels", with wheels/tires/rims/undercarriage produce external forces with or without braking
            • April 2021: We also need to mention "Effective Mass" as another possible explanation for M1DeltaV1 Not Equal M2DeltaV2
          • See Some Momentum Misconceptions which includes that statement and more issues to consider
          • See our SMAC paper from 1973 where we note the importance of including consideration of external forces
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