Problem set 2 -week 3 challenge : Anti-Characteristics

From the given information, the following parameters were calculated using the formulae:-

• wheel rate = spring rate*(motion ratio^2) for both front and rear
• load transfer= (total weight*throttle acc(g)*CG height)/ wheelbase*g
• Front axle weight after load transfer = FAW(static) - load transfer
• Rear-axle weight after load transfer = RAW(static) + load transfer
• Front end deflection = (load transfer *0.5)/wheel rate
• Rear end deflection = (load transfer*0.5)/wheel rate
• Pitch angle = tan inv((Front end deflection + Rear end deflection)/Wheel base)*180/pi
• Pitch gradient = Pitch angle/throttle acc(g)

From the given IC location details, the following anti characteristics parameters were calculated using the formulae:-

• Front anti-lift angle = tan inv((FICV - tire radius)/FICH))*180/pi
• Rear anti-squat angle = tan inv((RICV - tire radius)/RICH))*180/pi
• Front and Rear swing arm angle = tan inv((CG height/wheelbase))*180/pi
• Front anti-lift% = (Front anti-lift angle*(100-DR/100))/Front swing arm angle
• Rear anti-squat% = (Rear anti-squat angle*(100 - DR/100))/Rear swing arm angle

To eliminate the pitch angle, the rear IC height was fixed at 16in as mentioned and the pitch angle was brought to zero degrees by varying another parameter which is the Rear IC horizontal distance. The above anti characteristics parameters were calculated again leading the pitch to zero degrees. The front and rear end deflections with compensation were calculated using the formulae:-

• Front end deflection(with compensation) = (Front end deflection*(100-Anti-lift%))/100
• Rear-end deflection(with compensation) = (Rear end deflection*(100-Anti-squat%))/100

Since the vehicle in consideration is rear-wheel drive, the anti-lift% value is zero. Hence, the rear end deflection should be equal and opposite to the front end deflection in order to achieve zero pitch angle.

This desired value was achieved by varying the rear IC horizontal distance as the verticle distance is constrained to be at 16 inches as given in the question. This in turn makes the anti_squat percentage to be more than 100% which means when there is a longitudinal load transfer to the rear, the rear springs will extend instead of compressing.

The link to google drive is given below: -

https://drive.google.com/drive/folders/1uLTvrnL3IsjG1DyASIDugLfxNxN9-v8D?usp=sharing