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Using Data Acquisition

Part 4: Analyzing G-Forces
By Andrew Trevitt
Data Acquisition Buttonwillow Raceway Park
Buttonwillow Raceway Park... 
   
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Data Acquisition Buttonwillow Raceway Park
Buttonwillow Raceway Park
Data Acquisition Lateral And Longitudinal Forces
Lateral G (red) and longitudinal... 
   
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Data Acquisition Lateral And Longitudinal Forces
Lateral G (red) and longitudinal G (blue) forces are plotted here for a lap of Buttonwillow Raceway's west loop, recorded by our Racepak G2X system. A positive value for lateral G indicates a right-hand turn, a negative value the opposite. The top trace (black) is speed, shown here for reference. Note how longitudinal G forces change sharply from positive to negative at the end of each straight as the rider goes from accelerating to braking.
Data Acquisition Absolute Values
This graph shows absolute... 
   
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Data Acquisition Absolute Values
This graph shows absolute values (all negative numbers are changed to positive) for lateral and longitudinal G over the same full lap, in the same color scheme. Note that on the entrance to each corner, longitudinal G tapers off as the rider releases the brakes and enters the corner, while lateral G increases as the turn is initiated. Where the two lines cross is an indication of how late the rider is trail-braking into the turn. Likewise, on the exit of each corner the traces cross as the rider accelerates (adding longitudinal G) and straightens the bike out (reducing lateral G); the intersection point shows how aggressive the rider is getting on the gas exiting the turn.
Data Acquisition Traction Circle
A traction circle shows lateral... 
   
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Data Acquisition Traction Circle
A traction circle shows lateral forces on the horizontal axis and longitudinal forces on the vertical axis. Right turns are on the right, left turns on the left; acceleration is toward the top, braking toward the bottom. Using this layout the total acceleration can be plotted at any given time. For example, the point shown in the top left quadrant represents accelerating from a left-hand bend. Likewise, trail braking into a right-hand corner would generate data in the bottom right quadrant. More total force shows as a point closer to the outside of the circle; less force is toward the center. The characteristics of the tire and pavement dictate the maximum total acceleration available, shown visually as a circle.

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