Here's more data. Same road, same conditions (except zero wind - it's blocked a ridge & buildings to the NW).
This time I did 2 runs per PSI, at a 10 PSI interval
Car: 1999 Toyota Camry sedan V6
Tire info: 205/60/16 BF Goodrich Traction T/A, rated 44 PSI max sidewall.
Placard info: vehicle placard recommends 32 PSI front/rear @ max load.
Pressure Gauge: readings were taken with an Accutire digital gauge, 5-99 PSI rated, with a manufacturer accuracy claim of +/- 1% + 0.5
Weather: 20C / 68F, 4 kts N wind (NW sheltered roadway ran SW/NE)
Methodology:
- tires were pumped up to 60 PSI, drove to test route (< 5km), pressure adjusted
- car was driven up a small hill (approx. 6 ft. elevation, 8:1 slope), turned around and stopped at a marked point
- engine off, transmission in neutral, brakes were released
- car rolled down short hill onto a flat run-out road
- where the car stopped, the road was marked
- pressure was adjusted (dropped 10 PSI)
- rinse & repeat
- NOTE: two runs per PSI (blue), average (green)
I used a bicycle wheel to measure the rolling distances - counted revolutions from the starting point, then converted circumference to total feet.
Raw results for
PSI/feet travelled (1)/ feet travelled (2) / average
20 / 568 / 570 / 569
30 / 662 / 672 / 667
40 / 677 / 679 / 678
50 / 667 / 679 / 673
60 / 692 / 681 / 686
