In ,
Energy Saver wrote in part:
Each 60 pounds increases fuel consumption by 10%.
Although unnecessary weight decreases fuel economy, where do you get
this large number?
If you add 60 pounds to a mere 2,400 pound car, which is a lightweight
car in USA, you increase its weight by 2.5%.
Combine errands into one trip. Several short trips, each one taken from
a cold start, can use twice as much fuel as one trip covering the same
distance when the engine is warm. Do not forget that in the first mile
your car uses 8 times more fuel, in the second mile 4 times and only
after the fourth mile it becomes normal.
Although combining errands saves fuel and reduces wear on the engine,
where do you get such extreme numbers? These numbers sound extreme for
fuel consumption, that should show up in my fuel consumption, and they do
not. Could these be figures be for engine wear instead?
Or are you paying attention to a fuel gauge, whose reading can be
affected by temperature changes and by pressure changes in the fuel tank?
Source:
www.eere.energy.gov and
That particular page does not have any specific energy saving advice or
specific energy consumption figures that I saw at 5:35 PM EDT 4/18/09.
If that page provides a path to others having energy saving advice or
energy consumption figures, then you should post a link or a few further
along that path instead.
http://www.vcd.org/155.html
That one is in German and with metric figures. You should be saying
what you cited that page for, in some form what the page said, any
applicable metric figures as well as translations to figures in mile-based
units where applicable.
It may apply to your figures for usable gears at specific speeds of the
Porsche that you mentioned (and that I snipped). I have not actually
looked into seeing if that article supports your claims, though with maybe
10 minutes to an hour with some online German == English dictionary or
another I could check it out.
=============
Most of what you said does make sense. However, you should have done a
little more homework. Figures that sound unusual, extreme, "eye-popping"
or "Wow" should be investigated; treated skeptically with effort to see if
they get proven or disproven or turn out to be still under investigation
or debate, or turn out to be speculations with little effort noted yet to
prove/disprove.
Spouting or repeating hard-to-believe figures can harm your cause if it
can be shown that they are exaggerated or otherwise untrue.
=============
As for ideal RPM of a car engine - that is where the "torque curve" is
highest, for a specific degree of throttle that achieves the amount of
horsepower you need to use (as opposed to RPM where the "full throttle"
torque curve is highest).
If your car has an automatic transmission, ideal RPM in a specific
"speed/gear of the transmission" for a specific degree of throttle is
where torque times output RPM divided by input RPM is maximized. With
some automatic transmissions, maximizing fuel economy in stop-and-go
driving is not with gentrlest acceleration, but "slightly hard"
acceleration to get RPM to where ratio of output RPM to input RPM greater
(until gentler acceleration allows the transmission to shift to a "higher
gear").
I would say accelerate "slightly hard" until fast enough for letting up
on the accelerator pedal to make an automatic tranny to shift into 2nd,
then push from 2nd with some work otherwise done with 1st. Automatic
trannies appear to me to have lower losses in higher "gears". When
accelerating past 30-35 MPH or so, somewhere around there I often like to
ease up on the "gas pedal" to kick into 3rd to work a higher gear of the
automatic transmission where is has less "slip" (in terms of shortfall
from ideal ratio of output RPM to input RPM).
Some automatic trsnsmissions have a "lock-up torque converter" -
allowing ratio of output RPM to input RPM to match what is ideal, greatly
reducing (but not completely eliminating) losses in the automatic
transmission, very important with steady speed driving at 50-plus MPH.
My experience with 1993 and 1995 (especially 1993) Olds Delta 88
"Royale/LSS" indicates to me possibility of "torque converter lock-up" in
"second-highest gear" as well as highest since I sense 2 more "ranges
between sensed shifts" than the number of "gear ratios" that automatic
tranny for this car has been cited to me to have.
With a stick-shift, fuel economy in stop-and-go traffic is maximized by
accelerating when solidly in gear and doing so mainly at RPM where the
engine's torque curve (at degree of throttle in question) runs high.
One thing usually more than anything else when driving where there is a
stop sign every block - lower top speed usually reduces fuel consumption
more than anything else. Most of the energy output of the engine ends up
in the brakes, and "kinetic energy" of your moving car is proportional to
square of its speed. When driving where you have to stop (or where you
are "culturally allowed" to slow to "crash avoidance slow speed") every
block, then slower top speeds maybe around 20-25 MPH do well for fuel
economy.
Slower than 20 MPH for top speed before braking every block may
achieve further improvement in fuel economy when I have to drive where
there is a stop sign every block, but there gets to be a point where I
would rather not increase my driving time to reduce environmental impact,
cost-per-mile of driving, and wear-and-tear on my car.
Meanwhile, I do achieve maybe 15-18 MPG on average when driving a 1995
Olds Delta 88 where there is a stop sign or a traffic light every block,
and over 20 MPG with such a large oldish car on the portion of PA Route 3
between I-476 and Garrett Road. I did not do much worse with a 1993
version of that car, close to no worse at all once I get the automatic
tranny to kick into 3rd.
- Don Klipstein )