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

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data analysis

Quote:
 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.

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 04-12-2013, 03:15 PM #102 (permalink) Batman Junior     Join Date: Nov 2007 Location: 1000 Islands, Ontario, Canada Posts: 21,463 Blackfly - '98 Geo Metro Team Metro Last 3: 70.09 mpg (US) MPGiata - '90 Mazda Miata 90 day: 52.8 mpg (US) Winter beater Metro - '00 Chevrolet Metro 90 day: 73.57 mpg (US) Fancy Metro - '14 Mitsubishi Mirage top spec 90 day: 58.72 mpg (US) Thanks: 3,231 Thanked 6,085 Times in 3,153 Posts 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 __________________ Latest mods: 3-cylinder Mitsubishi Mirage. EcoMods now in progress... Ecodriving test: Manual vs. automatic transmission MPG showdown EcoModder has launched a forum for the efficient new Mitsubishi Mirage www.MetroMPG.com - fuel efficiency info for Geo Metro owners www.ForkenSwift.com - electric car conversion on a beer budget
 04-14-2013, 02:03 AM #103 (permalink) EcoModding Wannabee     Join Date: Sep 2011 Location: fabulous Las Vegas Posts: 14 Thanks: 6 Thanked 7 Times in 5 Posts more data analysis 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. __________________ "There's no tellin' where the money went" -- Robert Palmer, "Simply Irresistible" (1988)
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Quote:
 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.

 05-20-2013, 02:02 AM #105 (permalink) EcoModding Wannabee     Join Date: Sep 2011 Location: fabulous Las Vegas Posts: 14 Thanks: 6 Thanked 7 Times in 5 Posts 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% __________________ "There's no tellin' where the money went" -- Robert Palmer, "Simply Irresistible" (1988)
 05-21-2013, 01:24 PM #106 (permalink) Master EcoModder     Join Date: Sep 2012 Location: Texas Posts: 252 hX-TREME!!! - '97 Honda Civic HX 90 day: 54.75 mpg (US) 450sX-TREME!!! - '95 Nissan V8 240sx chodercycle - '06 kawasaki ninja zx6r 636 Thanks: 18 Thanked 43 Times in 23 Posts 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.
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Quote:
 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.

 08-12-2013, 01:15 PM #108 (permalink) Master EcoModder     Join Date: Jun 2013 Location: Texas Posts: 373 Thanks: 1,147 Thanked 92 Times in 75 Posts 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
 08-12-2013, 02:13 PM #109 (permalink) Pishtaco     Join Date: Jun 2009 Location: Bay Area, California Posts: 1,485 Mean Green Toaster Machine - '06 Scion xB Team Toyota 90 day: 48.92 mpg (US) Thanks: 56 Thanked 285 Times in 181 Posts 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. __________________ Darrell Boycotting Exxon since 1989, BP since 2010 Have you ever noticed that anybody driving slower than you is an idiot, and anyone going faster than you is a maniac? George Carlin Mean Green Toaster Machine 49.5 mpg avg over 53,000 miles. 176% of '08 EPA Best flat drive 94.5 mpg for 10.1 mi Longest tank 1033 km (642 mi) on 10.56 gal = 60.8 mpg
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Quote:
 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