[gone-ot]

...the following equation by LaClair (attributed to the late Dr. Dieterich J. Schuring, 1980, of Firestone) shows the relationship between tire pressure and tire rolling resistance:

TRR = (P/Po)^-0.4

...where:

TRR = tire rolling resistance, change
Po = original tire pressure, psi
P = new tire pressure, psi

...the above is a quantification of the following text by Dr. Schuring:

"Inflation pressure affects tire deformation. Tires with reduced inflation exhibit more sidewall bending and tread shearing. The relationship between rolling resistance and pressure is not linear, but it is consistent enough for rules of thumb to be applied. Schuring (1980) observes that for conventional passenger tires, an increase in inflation pressure from 24 to 29 pounds per square inch (psi) will reduce rolling resistance by 10 percent. For a tire inflated to pressures between 24 and 36 psi, each drop of 1 psi leads to a 1.4 percent increase in its rolling resistance. The response is even greater for pressure changes below 24 psi." [from: Tire and Passenger Vehicle Fuel Efficiency, Special Report 286, 2006]