I have heard and have confirmed with testing that mpg will increase by about .4 mpg or so for each PSI you increase for all 4 tires. Has anyone tested and documented this for sure? Also, has anyone calculated the point when PSI no longer increased the mpg? I know it's really not safe to exceed about 40-45 PSI in most tires and they will really begin to wear in the center at those pressures. Wondering at what PSI the increase stops.