Go Back   EcoModder Forum > EcoModding > EcoModding Central
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 06-02-2008, 12:27 PM   #1 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 19,316

Blackfly - '98 Geo Metro
Team Metro
90 day: 67.58 mpg (US)

ForkenSwift - '92 Geo Metro EV
Last 3: 95.68 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 38.25 mpg (US)
Thanks: 1,979
Thanked 4,683 Times in 2,342 Posts
Experiment: coast down distances (rolling resistance) @ various tire pressures

The purpose of the test was to get an idea of the difference in coasting distances in my '98 Metro/Firefly over a range of tire pressures, 20-60 psi.

EDIT Jan 23/09: Posted a summary of this thread at: http://metrompg.com/posts/tire-press...resistance.htm

Tire tested: 155/80/R13 Goodyear Invictas, rated 44 PSI max sidewall.

EDIT - 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

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: 19C / 66F, 10 km/h SSW wind (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 5 PSI)
  • rinse & repeat
  • NOTE: only one run per PSI
I used a bicycle wheel to measure the rolling distances - counted revolutions from the starting point, then converted circumference to total feet.

Ideally, I would have simply measured the coastdown distance from a constant speed at the same point on a level road, but my cruise control isn't working, and I didn't want to deal with the possibility of driver error (varying speeds). Even more ideally, I should have done multiple runs per pressure level.

Since the car accelerates from rest and coasts to a stop, the differences in pressure are amplified compared to a simple coastdown test.

Raw results for PSI/feet travelled

20 / 479.3
25 / 524.8
30 / 621.0
35 / 621.0
40 / 639.6
45 / 687.5
50 / 702.0
55 / 699.3
60 / 702.0




Attached Thumbnails
Click image for larger version

Name:	psi-coasting.gif
Views:	2762
Size:	10.7 KB
ID:	841  
__________________
Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
Ecodriving test:
Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L



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
  Reply With Quote
The Following 18 Users Say Thank You to MetroMPG For This Useful Post:
alexibu (04-08-2013), AndrzejM (04-01-2013), California98Civic (05-20-2013), Cd (10-13-2011), Daox (09-25-2014), drees (01-03-2012), fcporto (04-04-2013), justjohn (05-03-2011), kurzer (01-02-2012), MARTINSR (08-03-2010), mikeyjd (03-31-2013), RedDevil (04-04-2013), renault_megane_dci (04-07-2013), Sykomor (10-15-2011), UltArc (05-19-2013), user removed (04-01-2013), wyatt (04-05-2013), Xusn96 (09-25-2014)
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 06-02-2008, 12:46 PM   #2 (permalink)
Administrator
 
Daox's Avatar
 
Join Date: Dec 2007
Location: Germantown, WI
Posts: 10,081

CM400E - '81 Honda CM400E
90 day: 39.62 mpg (US)

Daox's Grey Prius - '04 Toyota Prius
Team Toyota
90 day: 38.47 mpg (US)

Daox's 04 Civic - '04 Honda Civic DX
90 day: 41.58 mpg (US)

Daox's Insight - '00 Honda Insight
90 day: 64.33 mpg (US)
Thanks: 1,604
Thanked 1,915 Times in 1,179 Posts
Very good info!
__________________
Current project: 2000 Insight 5 speed repair & build thread
  Reply With Quote
Old 06-02-2008, 01:04 PM   #3 (permalink)
Master EcoModder
 
NeilBlanchard's Avatar
 
Join Date: May 2008
Location: Maynard, MA Eaarth
Posts: 6,621

Mica Blue - '05 Scion xA RS 2.0
Team Toyota
90 day: 42.48 mpg (US)

Forest - '15 Nissan Leaf S
Team Nissan
90 day: 156.46 mpg (US)

Number 7 - '15 VW e-Golf SEL
TEAM VW AUDI Group
90 day: 155.81 mpg (US)
Thanks: 1,808
Thanked 1,769 Times in 1,068 Posts
Hello,

It is interesting to note that the plateau seems to happen roughly at the 44psi sidewall max pressure.
__________________
Sincerely, Neil



http://neilblanchard.blogspot.com/
  Reply With Quote
The Following User Says Thank You to NeilBlanchard For This Useful Post:
Cd (10-13-2011)
Old 06-02-2008, 01:45 PM   #4 (permalink)
Legend in my own mind
 
trikkonceptz's Avatar
 
Join Date: Apr 2008
Location: Homestead, Fl.
Posts: 927

Evil Pumpkin - '08 Scion xD RS 1.0 #1633
90 day: 35.45 mpg (US)

Silent Silver Killer - '10 Honda Insight EX
90 day: 51.5 mpg (US)
Thanks: 2
Thanked 13 Times in 12 Posts
Nice to see that 50psi seems to be the magic number ...
__________________
Thx NoCO2; "The biggest FE mod you can make is to adjust the nut behind the wheel"

I am a precisional instrument of speed and aeromatics
If your knees bent in the opposite direction......what would a chair look like???





  Reply With Quote
Old 06-02-2008, 04:03 PM   #5 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 19,316

Blackfly - '98 Geo Metro
Team Metro
90 day: 67.58 mpg (US)

ForkenSwift - '92 Geo Metro EV
Last 3: 95.68 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 38.25 mpg (US)
Thanks: 1,979
Thanked 4,683 Times in 2,342 Posts
Quote:
Originally Posted by Daox View Post
Very good info!
Not really. Very good info would have been multiple runs at each pressure level to ensure I was getting accurate readings.

(You can tell the accuracy is questionable by the pair of identical distances at different pressures.)

It's useful info as a "snapshot", but I wouldn't draw any hard & fast conclusions from it. Maybe it'll encourage other people to try it for their particular vehicles / tires.
__________________
Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
Ecodriving test:
Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L



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
  Reply With Quote
Old 06-02-2008, 04:33 PM   #6 (permalink)
dcb
needs more cowbell
 
dcb's Avatar
 
Join Date: Feb 2008
Location:
Posts: 5,032

pimp mobile - '81 suzuki gs 250 t
90 day: 96.29 mpg (US)

schnitzel - '01 Volkswagen Golf TDI
90 day: 53.56 mpg (US)
Thanks: 156
Thanked 264 Times in 207 Posts
Cool Test How fast were you getting up to? I'm wondering if the air drag at the higher speeds is what is leveling off the results.
__________________
WINDMILLS DO NOT WORK THAT WAY!!!
  Reply With Quote
Old 06-02-2008, 04:47 PM   #7 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 19,316

Blackfly - '98 Geo Metro
Team Metro
90 day: 67.58 mpg (US)

ForkenSwift - '92 Geo Metro EV
Last 3: 95.68 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 38.25 mpg (US)
Thanks: 1,979
Thanked 4,683 Times in 2,342 Posts
Not fast - 18.5 km/h @ 60 psi (the only time I checked).

But potentially approaching 28.5 km/h with the cross breeze (anyone want to do the vector calcs? ), but the road was also partially sheltered by trees & buildings, so I doubt I was seeing the full wind reported at the weather station.

I figure the varying breeze may have contributed to the pairs of matching results.
__________________
Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
Ecodriving test:
Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L



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
  Reply With Quote
Old 06-02-2008, 05:14 PM   #8 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 19,316

Blackfly - '98 Geo Metro
Team Metro
90 day: 67.58 mpg (US)

ForkenSwift - '92 Geo Metro EV
Last 3: 95.68 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 38.25 mpg (US)
Thanks: 1,979
Thanked 4,683 Times in 2,342 Posts
Based on my aero+rr spreadsheet, at 10 mph (16 km/h), the proportion of power required to overcome rolling/mechanical vs. aero losses is: 0.44 to 0.05 hp.

At 15 mph (24 km/h) it's 0.74 hp vs. 0.16 hp for rolling/aero.
__________________
Latest mods test: 15 mods = 15% MPG improvement: A-B test, 2007 Honda Civic 1.8L, 5-speed
Ecodriving test:
Manual vs. automatic transmission MPG showdown: Nissan Micra 1.6L



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
  Reply With Quote
Old 06-02-2008, 05:44 PM   #9 (permalink)
Dartmouth 2010
 
SVOboy's Avatar
 
Join Date: Nov 2007
Location: Hanover, NH
Posts: 6,427

Vegan Powa! - '91 Honda CRX DX
Team Honda
90 day: 66.52 mpg (US)
Thanks: 92
Thanked 110 Times in 79 Posts
Send a message via AIM to SVOboy Send a message via MSN to SVOboy Send a message via Yahoo to SVOboy Send a message via Skype™ to SVOboy
Mehbe some more people will get out there and look for some data, but that's encouraging stuff, I think.
  Reply With Quote
Old 06-02-2008, 05:54 PM   #10 (permalink)
Master EcoModder
 
ttoyoda's Avatar
 
Join Date: May 2008
Location: boston ma
Posts: 381
Thanks: 0
Thanked 5 Times in 5 Posts
"Not really. Very good info would have been multiple runs at each pressure level to ensure I was getting accurate readings. "
You did do well, and deserve the credit. Very-very good info would be to either measure the temperature of the tire before and after each run, OR take an air tank with you and do the test again, but INCREASE the air pressure after each run.
You might consider checking the tire pressure before you begin the run, and right after you finish, to see if there is a measureable difference.

  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hyperinflating tires CapriRacer Hypermiling / EcoDriver's Ed 237 03-23-2016 04:14 PM
Tire Engineer here - concerned about hyperinflating tires CapriRacer Introductions 48 09-26-2009 09:25 PM
Tire pressure (of winter tires) tasdrouille General Efficiency Discussion 20 08-12-2009 01:38 AM



Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com