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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 01-15-2014, 09:54 AM   #1 (permalink)
EcoModding Lurker
 
Join Date: May 2012
Location: MD
Posts: 18
Thanks: 0
Thanked 5 Times in 5 Posts
Nice summary of mileage stretching

At Fuelly.com:

Fuel Saving Tips | Fuelly

They even mention ecomodder!

MF

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 01-16-2014, 05:34 PM   #2 (permalink)
In the slow lane
 
songman's Avatar
 
Join Date: May 2013
Location: Southern England, UK
Posts: 47

Civic Type R - '08 Honda Civic
90 day: 38.19 mpg (US)
Thanks: 0
Thanked 9 Times in 6 Posts
Quote:
You often read tips to depress the clutch or drop the car into neutral downhill, on most modern cars with fuel injection this actually uses more fuel than leaving it in gear.

Fallacy, IMO. Yes, no fuel used. But less time spent coasting, because of engine drag.

Just EOC already.
  Reply With Quote
The Following 2 Users Say Thank You to songman For This Useful Post:
dirtydave (05-17-2014), Fat Charlie (01-17-2014)
Old 01-16-2014, 11:25 PM   #3 (permalink)
Master EcoModder
 
vskid3's Avatar
 
Join Date: Jun 2008
Location: Utah
Posts: 975

Civic DX (sold) - '97 Honda Civic DX
90 day: 34.15 mpg (US)

GTO (sold) - '04 Pontiac GTO
90 day: 22.62 mpg (US)

Green Brick (sold) - '06 Ford Escape Hybrid
90 day: 31.93 mpg (US)
Thanks: 193
Thanked 312 Times in 221 Posts
Quote:
Originally Posted by songman View Post
Fallacy, IMO. Yes, no fuel used. But less time spent coasting, because of engine drag.

Just EOC already.
I think the intent of that statement is for going downhill, where you would either have to engine brake or use the friction brakes to keep from going too fast. On flat land, yes, neutral is better, but going downhill, you might as well use some of the excess energy to spin the engine.
__________________


Camry Thread
E-Bike Thread
  Reply With Quote
The Following User Says Thank You to vskid3 For This Useful Post:
Cobb (02-01-2014)
Old 01-17-2014, 06:17 AM   #4 (permalink)
Master EcoModder
 
Join Date: Jan 2012
Location: United States
Posts: 1,756

spyder2 - '00 Toyota MR2 Spyder
Thanks: 104
Thanked 407 Times in 312 Posts
Quote:
Originally Posted by vskid3 View Post
On flat land, yes, neutral is better, but going downhill, you might as well use some of the excess energy to spin the engine.
Most hills aren't steep enough to warrant that. In the SFBA, the only freeway with a lower speed limit than my terminal velocity is Highway 92 off 280 going to San Mateo, where I can go about 75mph in neutral for several miles. Everywhere else the car will lose speed until 40 or lower, and my car is a featherweight aka it has terrible coasting.
  Reply With Quote
Old 01-17-2014, 03:21 PM   #5 (permalink)
Master EcoModder
 
basjoos's Avatar
 
Join Date: Dec 2007
Location: Upstate SC
Posts: 1,088

Aerocivic - '92 Honda Civic CX
Last 3: 70.54 mpg (US)

AerocivicLB - '92 Honda Civic CX
Team Honda
90 day: 55.14 mpg (US)

Camryglide - '20 Toyota Camry hybrid LE
90 day: 62.77 mpg (US)
Thanks: 16
Thanked 676 Times in 302 Posts
The lower your cd or the greater your weight, the more easily your car will exceed the posted speed limits on a downhill run unless you use braking to limit the speed. The aerocivic is also a featherweight at 2100 lbs, but with its low cd pushing its terminal velocity somewhere above 100mph, it will easily exceed 75 mph on any reasonable downhill run long enough for it to build up speed. It doesn't even have to be a steep downhill.
__________________
aerocivic.com
  Reply With Quote
The Following 2 Users Say Thank You to basjoos For This Useful Post:
dirtydave (05-17-2014), user removed (03-06-2014)
Old 01-17-2014, 05:59 PM   #6 (permalink)
The PRC.
 
Join Date: Oct 2009
Location: Elsewhere.
Posts: 5,304
Thanks: 285
Thanked 536 Times in 384 Posts
Quote:
Originally Posted by songman View Post
Just EOC already.
Mention EOC anywhere else and you will be put in the stocks for being a danger to everyone...
__________________
[I]So long and thanks for all the fish.[/I]
  Reply With Quote
Old 01-17-2014, 06:33 PM   #7 (permalink)
Master EcoModder
 
Join Date: Jan 2012
Location: United States
Posts: 1,756

spyder2 - '00 Toyota MR2 Spyder
Thanks: 104
Thanked 407 Times in 312 Posts
Quote:
Originally Posted by basjoos View Post
The lower your cd or the greater your weight, the more easily your car will exceed the posted speed limits on a downhill run unless you use braking to limit the speed. The aerocivic is also a featherweight at 2100 lbs, but with its low cd pushing its terminal velocity somewhere above 100mph, it will easily exceed 75 mph on any reasonable downhill run long enough for it to build up speed. It doesn't even have to be a steep downhill.
Yup, but it's fairly common that a car has 2x the drag of your car. I have around the same drag as a Prius but only 70% the weight. The second steepest long "hill" around here that I've seen is the Bay Bridge, where I top out at 40mph. A Prius would probably top out at 50mph, the speed limit.

Even a Mercedes E class pushing 4000 pounds and with a low Cd would probably have trouble getting to 60mph, but a Lexus LS or Mercedes S class pushing 5000-6000 pounds would probably necessitate engine braking down that moderate downhill, but that's not really the norm.
  Reply With Quote
Old 02-01-2014, 12:32 AM   #8 (permalink)
Moderator
 
Vman455's Avatar
 
Join Date: Feb 2012
Location: Urbana, IL
Posts: 1,935

Pope Pious the Prius - '13 Toyota Prius Two
Team Toyota
SUV
90 day: 51.62 mpg (US)

Tycho the Truck - '91 Toyota Pickup DLX 4WD
90 day: 22.22 mpg (US)
Thanks: 198
Thanked 1,797 Times in 937 Posts
Quote:
Originally Posted by basjoos View Post
The lower your cd or the greater your weight, the more easily your car will exceed the posted speed limits on a downhill run unless you use braking to limit the speed. The aerocivic is also a featherweight at 2100 lbs, but with its low cd pushing its terminal velocity somewhere above 100mph, it will easily exceed 75 mph on any reasonable downhill run long enough for it to build up speed. It doesn't even have to be a steep downhill.
Hold on--I'm remembering my Galileo: bodies of varying mass fall at the same rate. The heavier car will also have more rolling resistance. But, the heavier car will have more momentum. Has anyone proven empirically that in the case of two cars, with identical Cd and frontal area but different masses, the heavier car will roll faster downhill? Does the increased momentum of a heavy car outweigh (ha!) the increased rolling resistance at some point, and where is that point?
__________________
UIUC Aerospace Engineering
www.amateuraerodynamics.com

Last edited by Vman455; 02-01-2014 at 12:43 AM..
  Reply With Quote
The Following User Says Thank You to Vman455 For This Useful Post:
user removed (03-06-2014)
Old 02-01-2014, 09:29 AM   #9 (permalink)
Master EcoModder
 
euromodder's Avatar
 
Join Date: Jul 2010
Location: Belgium
Posts: 4,683

The SCUD - '15 Fiat Scudo L2
Thanks: 178
Thanked 652 Times in 516 Posts
Quote:
Originally Posted by Vman455 View Post
Hold on--I'm remembering my Galileo: bodies of varying mass fall at the same rate.
In vacuum

IRL, the rate of fall is determined by mass, shape & volume (body density and aero drag), the length of the fall and air density.
If you don't believe that, don't go sky jumping

That's why it took until Galileo for people to realise the concept.


Quote:
Has anyone proven empirically that in the case of two cars, with identical Cd and frontal area but different masses, the heavier car will roll faster downhill?
There's no real need to try it.
Gravity usually exceeds rolling resistance.

The main thing you might need to overcome is inertia, i.e. getting the car rolling - which takes the most force.
Once rolling, the heavier car will accelerate away from the lighter one.
__________________
Strayed to the Dark Diesel Side

  Reply With Quote
Old 03-05-2014, 11:13 PM   #10 (permalink)
Moderator
 
Vman455's Avatar
 
Join Date: Feb 2012
Location: Urbana, IL
Posts: 1,935

Pope Pious the Prius - '13 Toyota Prius Two
Team Toyota
SUV
90 day: 51.62 mpg (US)

Tycho the Truck - '91 Toyota Pickup DLX 4WD
90 day: 22.22 mpg (US)
Thanks: 198
Thanked 1,797 Times in 937 Posts
Quote:
Originally Posted by euromodder View Post
In vacuum

IRL, the rate of fall is determined by mass, shape & volume (body density and aero drag), the length of the fall and air density.
If you don't believe that, don't go sky jumping

That's why it took until Galileo for people to realise the concept.



There's no real need to try it.
Gravity usually exceeds rolling resistance.

The main thing you might need to overcome is inertia, i.e. getting the car rolling - which takes the most force.
Once rolling, the heavier car will accelerate away from the lighter one.
Quote:
Originally Posted by Vman455 View Post
...in the case of two cars, with identical Cd and frontal area but different masses...
I'll rephrase my question: is there a point at which the inertia of a more massive body overcomes the increased rolling resistance of that body such that it will roll downhill faster than an aerodynamically-identical, less massive body? I see people all the time claiming that a heavy car will roll downhill faster than a lighter, but I've never seen any evidence to suggest this is so.

__________________
UIUC Aerospace Engineering
www.amateuraerodynamics.com
  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com