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This is an expansion of a portion of the previous page. Specifically, the procedure by which the 400 pounds per inch and 600 pounds per inch front spring rates were determined will be detailed. That portion of the driveshaft reaction torque absorbed by the front suspension will act to unload the right rear (and, of course, load the left rear). If, however, the distribution of the weight transfer favors the right rear in the proper proportion, the unfavorable loading of the rear tires will be canceled. It should be intuitively obvious that, if the right front has no suspension (is solid) and the chassis is assumed rigid, all of the weight transfer would initially be taken from the right front wheel loading. Extrapolating from this, we can say that...if the front suspension springs are not equal in rate...KsubR/(KsubR+KsubL) of the weight transfer will go to the right rear and KsubL/(KsubR+KsubL) will go to the left rear. (Each "sub" name refers to a spring rate.) Further, we can say that {KsubR/(KsubR+KsubL) - 1/2}, when multiplied by the weight transfer, will equal that extra right rear loading which occurs when KsubR is greater than KsubL. The torque to be canceled equals the wheelbase (108) times the rear tire radius (14) and divided by the CG height (18), and the axle ratio (4.11). When this is divided by the rear track (60), we have that which is enclosed by {} above. It is convenient to work with the ratio of KsubR to KsubL. So, if the numerator and denominator of KsubR/(KsubR+KsubL) are divided by KsubL, we have RATIO/(RATIO+1). Using this in the {} relationship and setting it equal to the torque to be canceled, we can solve for RATIO. RATIO is found to be equal to 5.27. If, in the example of the previous page, spring rates of 175 and 825 pounds per inch had been used, plot "C" would have been on the abscissa (horizontal), meaning that left and right rear wheel loadings would be equal throughout the launch. The above spring rate difference is sizeable, even on an oval track car. For this reason, I do not recommend this as the only form of suspension asymmetry. If, however, the traction dyno indicates that full cancellation of the driveshaft torque has not been achieved by some other form of asymmetry, less radical differences in spring rate could be used to "fine tune" the tire loading. |