Experiment: coast down distances (rolling resistance) @ various tire pressures

[LioNiNoiL]

Originally Posted by MetroMPG

More inflation vs. rolling resistance data for the pile.

Thank you for your diligence and care. Since data analysis (especially small-sample analysis) comprised the second half of my professional career (from which I am now retired) I entertained myself tonight by exercising some remaining brain cells with my own spreadsheet (OpenOffice Calc) analysis of these data, verified with software by Richard Lowry at Vassar:

Spearman rank correlation* (SRC) between 70psi and 60psi of feet travelled is -0.488, a weak (insignificant) decrease of feet above 60psi.
Including the 50psi data gives a SRC of +0.133, a very weak (insignificant) increase of feet above 50psi.
Including the 40psi data gives a SRC of +0.644, a strong (significant at 0.012 level) increase of feet above 40psi.
It's therefore clear that increasing pressure above 40psi results in an increase in feet, and that increasing pressure above 50psi does not.

*chosen because the data are non-linearly related.

[MetroMPG]

Thanks for the analysis! I don't suppose you'd care to turn your skills to this related test ...

Also tested Oct 13, 2011... Bridgestone RE92 tires, multiple runs at pressures from 20-70 PSI. See this post: Experiment: coast down distances (rolling resistance) @ various tire pressures

[LioNiNoiL]

psi feet

20 568
20 570
30 662
30 672
40 677
40 679
50 667
50 679
60 681
60 692

The same type of analysis of these earlier data is a bit more interesting than the previous analysis, because of the high SRC (+0.8944) between 60psi and 50psi, which has low significance (at 0.167 level) due to small sample size of only four pairs of data.
Including the 40psi data reduces the SRC to +0.667 with greater significance (at 0.074 level) because of more data.
Including the 30psi data increases the SRC to +0.761 significant at 0.014 level.
Including the 20psi data further increases the SRC to +0.877 highly significant at 0.0004 level.
In these data, it appears that increasing pressure to 60psi may result in an increase in feet (unlike the previous data) but the significance is low enough to diminish our confidence in this result. As is stated nearly always in such cases, we need more data.

[mikeyjd]

Originally Posted by LioNiNoiL

psi feet

20 568
20 570
30 662
30 672
40 677
40 679
50 667
50 679
60 681
60 692

The same type of analysis of these earlier data is a bit more interesting than the previous analysis, because of the high SRC (+0.8944) between 60psi and 50psi, which has low significance (at 0.167 level) due to small sample size of only four pairs of data.
Including the 40psi data reduces the SRC to +0.667 with greater significance (at 0.074 level) because of more data.
Including the 30psi data increases the SRC to +0.761 significant at 0.014 level.
Including the 20psi data further increases the SRC to +0.877 highly significant at 0.0004 level.
In these data, it appears that increasing pressure to 60psi may result in an increase in feet (unlike the previous data) but the significance is low enough to diminish our confidence in this result. As is stated nearly always in such cases, we need more data.

Thank you for optimizing our understanding of the existing data. I've been rocking 55-60 psi on my cars since I came across this thread and I've been happy with the balance between ride comfort and rolling resistance. Thanks to everyone who added to this thread.

[LioNiNoiL]

I do a lot of hiking, and a fellow hiker has a Ford Excursion (huge SUV) who routinely has 65psi in his tyres (recommended for 45psi) having measured an increase in fuel economy by ½ mpg (more than that at 45psi) which for him is about 5%

[Jakins]

on a past road trip i stopped at a truck stop and cranked my PSI waay up. idk how much because i didnt have a gauge but it felt alot different. way more rough and easyer to stear without power steering. but when i got home the car was hopping. the tires bulged out and were ruined. so now im afraid of pumping them up real high. who knows. maybe i cranked them up like over 70 psi or something dangerous. they were real old tires too.

[justme1969]

Originally Posted by Jakins

on a past road trip i stopped at a truck stop and cranked my PSI waay up. idk how much because i didnt have a gauge but it felt alot different. way more rough and easyer to stear without power steering. but when i got home the car was hopping. the tires bulged out and were ruined. so now im afraid of pumping them up real high. who knows. maybe i cranked them up like over 70 psi or something dangerous. they were real old tires too.

Ive said it many times tires dont survive over airing like back in 80s/90s
I did same the did it again just to be sure I was stupid! lol
dont take car tires past max inflation.

[Joggernot]

Long ago people were putting "airplane" tires that could be pumped to 300 psi on their cars for best mileage. Has anyone here done this? Has anyone checked to see if airplane tires would fit a 15 or 16 rim?

Joggernot

[SentraSE-R]

Aircraft tires aren't DOT approved, ergo not street-legal. You'd have to run them at ~200 psi, and fill them with water if you wanted to overinflate them.

[jime57]

Originally Posted by justme1969

Ive said it many times tires dont survive over airing like back in 80s/90s
I did same the did it again just to be sure I was stupid! lol
dont take car tires past max inflation.

It probably depends some on the tire brand and model. Insight owners have been very successful running 80 psi in the Bridgestone RE-92. There are lots of examples, with no recorded examples of damage, that I am aware of. I do suspect that damage would be more likely with old tires.

However, the gains in MPG at 60psi+ are very small if any. The Insight is a very difficult car on which to make such measurements, so it is a bit difficult to really know