mpg and weight - Page 3 - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 07-14-2007, 10:51 PM   #21
Registered Member
 
Join Date: Jun 2007
Posts: 358
Country: United States
Send a message via MSN to baddog671
How does weight not matter in PG? Extra weight could increade the time it takes to pulse back up to speed, and extend the distance covered in glide. I doubt these would balance each other out, so it would matter...

Look at the statistics of F1 race cars. They have extremely high reving huge engines going extreme speeds and get insane mpg. F1 cars are LIGHT, they dont even paint them to avoid the extra weight of a millimeter thick of paint....
__________________

__________________
baddog671 is offline   Reply With Quote
Old 07-14-2007, 10:57 PM   #22
Senior Member
 
Join Date: Jul 2010
Posts: 278
Country: United States
Location: CT
But the longer glides do cancel out the more costly pulses.

And the F1's FE is due mostly to aerodynamics, not necessarily weight.
__________________

Wyldesoul is offline   Reply With Quote
Old 07-14-2007, 11:04 PM   #23
Registered Member
 
Join Date: Jun 2007
Posts: 358
Country: United States
Send a message via MSN to baddog671
I have lightened my car nearly 100 pounds off the factory dry curb weight and have seen an increase in FE and overall power. I can cruise in higher gears than I have before, and that is a direct weight to FE improvement. I can also leave stoplights with less effort on the engine.

There are no flats around here, so I cannot vouche for "flat-driving", but I promise you, weight has a dramatic affect on mpg when you start cruising up a hill.
__________________
baddog671 is offline   Reply With Quote
Old 07-14-2007, 11:12 PM   #24
Senior Member
 
Join Date: Jul 2010
Posts: 278
Country: United States
Location: CT
I know. I never denied it made accelerating easier on FE to be lightweight. I never denied it had an overall improvement for FE to be lightweight.

I just said it made no difference for constant, level diving, or more appropriately, P&G.
Wyldesoul is offline   Reply With Quote
Old 07-14-2007, 11:23 PM   #25
Supporting Member
 
Join Date: May 2007
Posts: 319
Country: United States
Quote:
But the longer glides do cancel out the more costly pulses.
Do we know this for sure?
McPatrick is offline   Reply With Quote
Old 07-14-2007, 11:52 PM   #26
Registered Member
 
Join Date: Jun 2007
Posts: 71
Country: United States
I think that one of the factors that hasn't been mentioned yet is what I've come to believe as a fundamental "FE driving technique" which is the "when driving up hill, set the power (RPM) and accept whatever MPH you get." For those who mentioned Newton's Second Law of Motion, that's like having a constant Force. So, given a constant Force, if Mass is relatively low, then Acceleration will be relatively high. Similarly, given a constant Force, if Mass is relatively high, then Acceleration will be relatively low. What that means is that for a heavier loaded car, it means it's going to take a longer time to get to say 55 MPH than a lightly loaded car. However, since fuel efficiency is related to the engine RPM reading on the tachometer more than the MPH reading on the speedometer, I think the "set the power (RPM) and accept whatever MPH you get" driving method basically cancels out the weight factor. Now, if you live in a part of the country with minimum speed limits then you wouldn't be able to "accept whatever MPH you get" then that would necessitate a higher throttle setting in order to move the relatively heavier car at a proportionally higher acceleration to achieve and maintain the minimum speed limit. In that case, yes I agree that a heavier car would have a negative effect on your fuel economy.

So to summarize those who posted before me, the answer is "it depends."
__________________
GasSavers_rGS is offline   Reply With Quote
Old 07-15-2007, 05:22 AM   #27
Senior Member
 
Join Date: Jul 2010
Posts: 278
Country: United States
Location: CT
For my car, yes.

Usually it's at 3600 pounds or so (With me in it) and on trips where I'm going a consistent 65 mph, I get an average of 35-45 mpg.

When it was loaded down to nearly 4500 pounds for that vacation, I got that same average of 35-45 mpg at 65 mph.
(And that was over 600 miles of highway cruising, so it was a pretty good way to average. But note, I'm ONLY counting the lengthened interstate trips where I didn't touch the brakes. The total average for the trip was 29.7MPG. Th 100 miles of city driving I did in that one trip lowered my MPG by that much! If I were lighter, they wouldn't have)

Nearly a thousand pounds extra weight, and it didn't change my highway MPG.

Wreaked havoc with my city MPG because I had to use the brakes and I couldn't reclaim that extra fuel used to accelerate in longer coasts.

The physics works. My real world experience works.
On the highway, weight plays little factor in MPG, so long as you don't touch the brakes.

You won't go as fast, but you'll go the same distance on the same set energy. And that is counting friction into the equation. The rolling resistance is higher for heavier cars, yes, but not by enough to really matter. With equal drag coefficients and equal force being applied, the weight won't effect MPG.

If you don't ever touch the brakes.

That's the key sentance. And therefore, since people always will touch the brakes.

Lighter cars will ALWAYS get better real world MPG than heavier cars. Because you will ALWAYS use your brakes.
Wyldesoul is offline   Reply With Quote
Old 07-15-2007, 06:01 AM   #28
Registered Member
 
skewbe's Avatar
 
Join Date: Jan 2007
Posts: 771
Country: United States
Quote:
Originally Posted by Biffmeistro View Post
...If you don't ever touch the brakes...

That's the key sentance. And therefore, since people always will touch the brakes.

Lighter cars will ALWAYS get better real world MPG than heavier cars. Because you will ALWAYS use your brakes.
That's the key here, one of the best hypermiling tips is to drive like you dont HAVE any brakes, which is not "status quo" driving, so lets not make statements like "ALWAYS" or "Real World", ok?

But I would agree in general, heavier cars will get worse mpg (unless the extra weight is an efficient energy recovery system or something)

But for a given car, it *may* be possible to "fine tune" the weight to local conditions for best mpg.
__________________
Standard Disclaimer
skewbe is offline   Reply With Quote
Old 07-15-2007, 06:53 AM   #29
Senior Member
 
Join Date: Jul 2010
Posts: 278
Country: United States
Location: CT
To be utterly honest, when has anyone ever made a trip without touching the brakes once?

If anyone can tell me that they ever ONCE made a trip where they NEVER touched the brakes, only ever used coasting to slow themselves down, I will most definitely eat crow.
Wyldesoul is offline   Reply With Quote
Old 07-15-2007, 07:10 AM   #30
Registered Member
 
skewbe's Avatar
 
Join Date: Jan 2007
Posts: 771
Country: United States
"Never" is not the upper limit, nor a good choice for a debate. But I use them infrequently enough and as little as possible that I probably have made a few trips around town without using them, sure.

Think about all the variables, and how they might be different from one situation to another (like the distance between hills, how much the wind is gusting, how well trained the driver is, how is the car geared, ad-infinitum),

Once you know everything in the universe then it is safe to use words like always and never
__________________

__________________
Standard Disclaimer
skewbe is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
total fuel cost for fill-up instead of price per gallon EmptyH Fuelly Web Support and Community News 1 08-26-2008 12:14 PM
MID Install SVOboy Experiments, Modifications and DIY 33 06-04-2007 11:27 AM
Electric bikes banned in Chinese city to make room for cars MetroMPG Electric and Solar powered 4 11-24-2006 08:29 AM
Electrical power and cars. DracoFelis Automotive News, Articles and Products 2 09-16-2006 02:31 PM
"active" aero grille slats on 06 civic concept MetroMPG General Fuel Topics 21 01-03-2006 01:02 PM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 01:39 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.