Hi,
I picked up the following graphs from:
Gyenes, L. and Mitchell, C.G.B., "The Effect of Vehicle-Road Interaction on Fuel Consumption," Vehicle-Road Interaction, ASTM STP 1225, B.T. Kulakawski, Ed., American Society for Testing and Materials, Philadelphia, 1994, pp. 225-239.
Tire inflation lookup table:
kN/m**2 - psi
200 - 29
225 - 33
250 - 36
275 - 40
300 - 44
325 - 47
350 - 51
375 - 53
Speed lookup table:
km/h - miles per hour
80 - 50
90 - 56
100 - 62
110 - 68
120 - 75
Vehicle drag is a function of rolling resistance and drag times the velocity squared. However, tire rolling resistance is not a linear function with speed and these charts give a clue.
Bob Wilson