[jime57]

I tried these tests myself and got a slightly different result, but only slightly.

I think that one potential problem the OP had was that his method did not adequately warm up the engine and transmission, so that viscous drag changed somewhat during the tests. I thoroughly warmed up my engine and transmission before my tests, and I left the engine running during the entire cycle so that engine heat would stabalize the transmission, final drive and inside CV joints. All my test runs were engine on, transmission in neutral. Of course I tested the RE92's on an Insight Gen1.

I only tested the very top of the pressure scale because I was intensely curious about the reversal at high pressure. My results are:

@80 psi
739.5', 740.0', &743.0'
Ave=740.8'

@70 psi
739.0', 739.5', & 740.5'
Ave+739.7'

@60 psi
736.0', 737.0', &740.0'
Ave=737.7'

@50psi
729.0', 731.0', 733.0'
Ave=731.0'

Steeper hill, longer runout.

I have very little confidence in this kind of "splitting hairs" on an experimental basis, but at least MY data showed a continued increase even to 80 psi. I'm not bragging because I think all this top end tire pressure stuff is clearly in the noise and various errors probably swamp any significant findings. If I did the test again tomorrow, the results might be different, and I don't think either result would mean much. When I get a nice day, I intend to drive my long test course at 70&80 psi and see if the fuel economy differs. After all, that is the real test. JMO