Firstly, I love this test and applaud your effort. Thank you for sharing.
In particular, I think the triplicate measurements to reveal variation was essential.
Quote:
Originally Posted by 3-Wheeler
I suppose one could *randomize* the order in which each test is run in order for any *heating effect* to reveal itself in the data.
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I agree with Jim; randomizing the order of the tests is a common practice. With multiple measurements and random order, you don't need to worry about the other factors such as wind, etc. so long as you are consistent in your method. However I think it's probably fine you didn't. Indeed, randomizing would have been a pain (lots of work to pump and decreasing air). If you're very keen and have a fast air pump, I would suggest instead, as a more practical solution, to do the test in reverse order (i.e. increasing the air pressures). Perhaps that would reveal if there was a confounding variable we need to be concerned with.
What I'm more interested in is at what psi does your tread wear evenly? This is easily determined with the chalk test. Draw a line across the tread of your tires, drive a while, and see if the chalk is wearing off evenly. It's usually helpful to draw multiple lines at different positions so when you stop, at least one will be readily visible. Perhaps test both rear tires only.
Lastly, I would strongly suggest that no one exceed the maximum recommended tire pressure for daily driving for safety reasons. Although it's great to have the numbers in the test. Furthermore it hasn't been shown that exceeding the max has any benefit; a couple more runs and we can do a statistical test (e.g. Student's T).
PS. in the offroad truck scene, many fill to the max psi for freeway driving in order to save gas, but once offroad, we drop the psi way down (e.g. 6-8) for traction. I appreciated having this study actually test this common assumption.