Go Back   EcoModder Forum > EcoModding > Hypermiling / EcoDriver's Ed
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 02-17-2009, 01:17 PM   #1 (permalink)
aero guerrilla
 
Piwoslaw's Avatar
 
Join Date: Oct 2008
Location: Warsaw, Poland
Posts: 3,538

Svietlana II - '13 Peugeot 308SW e-HDI 6sp
90 day: 58.1 mpg (US)
Thanks: 1,056
Thanked 630 Times in 396 Posts
Wrong numbers

I was surfing Polish web pages to see what they have to say about saving fuel and it's mostly "n steps to increasing your FE". In one 12-step plan, step #10 advises to reduce your speed. OK, we all know that, but here comes the fun part:
Quote:
You will increase your FE by 15% if instead of driving 100 km/h you go 85 km/h."
I know enough about aerodynamics (but please correct me if I screw something up) to tell that a 15% reduction in speed reduces the drag by more than 15%. Drag is proportional to the square of velocity, so if 100 km/h is 17.65% faster than 85 km/h (100=1.1765x85), then the drag @ 100km/h is over 38.4% greater than at 85 km/h. In other words, the drag @ 85 km/h is about 72.24% of what it is @ 100 km/h. So drag decreases by 27.75%. Add to that losses from other sources like rolling resistance and you're saving a lot.

If you are telling someone to slow down to save fuel, 30% is a better argument than 15%. Not everyone liked math at school

__________________
e·co·mod·ding: the art of turning vehicles into what they should be

What matters is where you're going, not how fast.

"... we humans tend to screw up everything that's good enough as it is...or everything that we're attracted to, we love to go and defile it." - Chris Cornell

Piwoslaw's Peugeot 307sw modding thread

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 02-17-2009, 01:34 PM   #2 (permalink)
X-Frenchy: very
 
groar's Avatar
 
Join Date: Jun 2008
Location: Toulouse, France
Posts: 595

scenic - '01 renault scenic
90 day: 43.09 mpg (US)

megane - '97 renault megane classic
Diesel
90 day: 72.53 mpg (US)

dennisius - '06 Toyota Prius
Team Toyota
90 day: 69.27 mpg (US)
Thanks: 9
Thanked 34 Times in 23 Posts
Certainly a simplification for simple people. On a highway trip I have lowered my consumption by 33% by lowering my speed by 11%.

Aero isn't the only force. Rolling resistance is also important. If we are minimizing RR, simple people will keep their tires underinflated. The eco-driving advises generally says to keep the tires at door placard.

You can play with this : http://www.geocities.com/frontsidesk8er/delsolaero.xls

Denis.
__________________
Save money & CO2 at home : http://ecorenovator.org/
Created and managed by the creators of http://ecomodder.com/
---
Earth and health are priceless, so are kilotank and AT-PZEV
Best Mégane tank: 1268.9mi @ 77.847 MPG(US)
2008/06-2011/10 saving:
  • 5725.5 kg CO2 (5342.6+382.9)
  • Diesel / Money: 42.17% = 2446.25€ = 3357.26$


---
megane : thread - kill switch.
  Reply With Quote
Old 02-17-2009, 02:19 PM   #3 (permalink)
EcoModding Apprentice
 
Bicycle Bob's Avatar
 
Join Date: May 2008
Location: N. Saskatchewan, CA
Posts: 1,688

Appliance White - '93 Geo Metro 4-Dr. Auto
Last 3: 42.35 mpg (US)

Stealth RV - '91 Chevy Sprint Base
Thanks: 84
Thanked 397 Times in 277 Posts
"- the drag @ 85 km/h is about 72.24% of what it is @ 100 km/h. So drag decreases by 27.75%. Add to that losses from other sources like rolling resistance and you're saving a lot."

Both wind drag and rolling resistance burn gas, but the rolling resistance is linear with speed, so for back-of-envelope estimate, it is somewhat Subtracted from the savings implied by the aero calculations. Also, the engine is usually less efficient at lower speeds. The scan gauge trumps all theories, though.
  Reply With Quote
Old 02-17-2009, 09:53 PM   #4 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,238

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.07 mpg (US)

Winter beater Metro - '00 Chevrolet Metro
90 day: 61.98 mpg (US)

Fancy Metro - '14 Mitsubishi Mirage top spec
90 day: 58.72 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)
Thanks: 3,796
Thanked 6,656 Times in 3,448 Posts
Quote:
Originally Posted by groar View Post
An expanded version of that spreadsheet is now available as an online tool here at EM:

Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

__________________
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: Oops, I did it again! Bought another cheap, 3-cylinder Mirage. Mods 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
  Reply With Quote
Reply  Post New Thread


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
What could be wrong if im only getting 40mpg in my 1990 CRX HF? dylanu EcoModding Central 13 10-08-2008 12:50 PM
Think Motorcycles and Scooters are Great for the Environment? Wrong! SuperTrooper EcoModder Blog Discussion 13 09-13-2008 10:01 AM
Crunching Numbers... jdwave EcoModding Central 6 08-01-2008 06:12 PM
EOC Question - what did i do wrong? Doofus McFancypants Hypermiling / EcoDriver's Ed 12 02-15-2008 01:18 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com