Heavy Truck Tire properties

[MSI]

Q: I’m simulating a heavy truck collision with a dual/tandem rear axle.
• The load on each of the two front tires is ~4000 lbs
• The load on combined rear axles is ~12000 lbs
• There are 8 tires in the combined dual/tandem rear axles
To calculate the cornering stiffness for each side of the rear axle assembly in M-SMAC, I used the following formula:
EQN#1:(Avg. weight on each of the 8 rear tires) X (recommended CS at 1500 lbs load [13%]) X (4 tires per side) = 780 lb/deg
Is this is consistent with the recommended approach?
2nd Question: Is the following a valid equation:
EQN#2:(TOTAL weight on rear axles divided by two) X (recommended CS at 1500 lbs load [13%]) X (4 tires per side) = 3131 lb/deg

A: For the per tire weight of 1500 lbs, the equation you present, EQN#1, is correct. Obviously the CS % needsto be adjusted if the 'weight per tire' changes.
See our Truck Tire properties section of the msmac Input Manual for additional information.
Answer to 2nd Question: EQN#2 appears to have an error in the calculation procedure. It calculates the total weight per side, perhaps to calculate an 'equivalent single tire' cornering stiffness value?
So first for a tire with a 6000 lbs load, a CS 13% multiplier may not be correct. And secondly, why do they then multiply the result by 4?
Small angle cornering stiffnesses of tires are a function of the weight on the tire.
For additional information see:
“Effects of Tire Porperties on Truck and Bus Handling” by Ervin, Winkler, Bernard & Gupta, UMTRI, NTIS PC-263 878.
"Representation of truck tire properties in braking and handling studies: the influence of vertical load on side force characteristics. Final report" by Balderas, L., UMTRI, NTIS Order PB 89 143002/AS
"Representation of truck tire properties in braking and handling studies: the influence of pavement and tire conditions on frictional characteristics. Final rep" by Balderas, L., UMTRI, NTIS Order PB 90 215104/AS