Fuel economy myths

Yes that is right, i did mean to mention that. many of them only have 1
axle on the rear as well.

Those little streets are so small you wouldn't want anything else.
Trucks and trailers look so small there in comparison to what we have
rolling down the highway.

 

the cars on the autobahn would also see the optimum efficient operation at 55
mph according to what i was reading like you said the law of physics applying
here
the magic number of 55 is used because of the optimum efficient operation and
it was studied long and hard by the epa and gm before that figure was picked
as a standard
setting the speed limit to 55 would also create a gasoline inventory excess
that would back up the refineries so much so
that the winter and summer blend refining schedule would interfere with the
season blending, they now have to use by epa law.
it would effectively shut them down and they would have to give gas away to
make room for the next blend coming in
that is one reason why we see gas prices drop before summer and before winter
so they can make room for the new blends
i have a customer who works for marathon oil a higher up exec. and those are
his words to me as he hands me a gas card as a tip instead of cash
i drive a rt dalota and use the eway and i drive 55 to help my cut fuel bill
and see folks driving by me so i am not stuck in those wolf paks of cars so i
get less stone chips too

 

I suspect that it has to do with other things, such as there's some
threshold that you start approaching some force threshold beyond which
your arms have trouble resisting on a sustained basis with the force
increasing by the square of the speed (I think) - to the human mind that
threshold appears as some magic switch point. To someone with slightly
stronger arms, the square law increase in wind force is going to make
that threshold appear at some higher but approximately the same speed,
so when the two people talk, they're going to agree that at around 55
mph, things "really" change.

Not sure of the validity of comparing an arm to a car body anyway.
There's no question that some cars are more efficient at speeds higher
than 55 - as posted by some here. I think you have fallen into the
exact trap I was warning about of making a law of physics about the
so-called 55 mph sweet spot. Wind resistance felt on a human arm on a
motorcycle is not very convincing to me. Watching fuel mileage readouts
at different speeds in different (varying degrees of streamlining and
gearing) vehicles is more convincing.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Nice run-on, dipshit. 55 supposedly cut back on accidents. It
didn't happen. Now, if your little car is at full throttle to get to
55, you might save gas by not trying to do 60, but for cars with
overdrive, going 40 uses more gas than going 60. Your theory, along
with your posting method, is flawwed.


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I suspect it's all in his head. Unlike in a cage, you notice
everything more as you go faster on a bike.

It actually helps to prove your point. If you're riding at 55 into a
20 mph wind, the "feeling" should be different than if you're riding
WITH said 20mph wind.

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You know it makes no sense at all. Some cars are absolutely more
efficient at higher speeds than 55 mph. What that says is that the
optimum speed can be designed into the vehicle by body design and
gearing, not to mention engine design (cams, intake tuning, etc.) and
ignition tuning curves.

Some cars absolutely get better mileage at higher speeds than others.
That's the starting point for my argument (that optimum speed for fuel
mileage can be designed in and that 55 mph is not dictated by the laws
of physics as the inherent optimum speed).

 

True.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Southwestern Ontario - what can I say??
In Kitchener Waterloo the prices are generally higher than Toronto or
Hamilton, It usually goes higher before it drops, then it drops
farther.

 

Around the northeast US, and I suspect most of the US, it would be a very
rare thing to see a $1.00/gallon swing in the price of gas - unless of
course we're talking about an increase. As prices have declined some from
the high of a short time ago, we really have not seen a $1.00 decline over a
period of greater than a year.

 

Must be nice I'm in Durham and I don't recall seeing anything below 92
in several months. In fact, when I saw it at 92 a few days ago, I was
really stunned, as it seemed to have been hovering at 95 or so for a couple
of weeks.

 

Apparently you haven't been inside a true sub-compact car then. Big
difference in space.

 

I agree. I have driven both a 1991 Hyundai Excel and a 2007 Prius and I am
6' 2" tall and 300lbs. The Excel felt like a sardine can to me but I was
just fine in the Prius. My main vehicle until a rod bearing spun was a 1992
Dodge Dynasty 3.3L that I also fit fine in.

 

It really doesn`t matter how slippery the body (unless someone comes up
with some magic to drop below appx 3.0 which is the current norm, as soon
as you go fast enough to creat a measureable wind resistance from that
point ultimate efficiency will drop off. No amount of gearing will increase
it at that point, unless you drop weight or increase efficieny of the power
plant or drive train losses. If you vechiel is getting better milage at
above 55 than at or below it, it is comprimised in one other department and
could do better. The laws of physics can not be changed only the paramaters
varied. KB

 

It can go both ways, but I took it as questioning the source of power
for recharging. It's a valid question, but it certainly covers a wider
topic than only vehicles.

Granted. But the average American doesn't give two dumps about any of
that. He/she simply wants to pull in to a refueling station, spend no
more than 10 minutes there, then take off for another 300 miles and do
it again when the needle is hovering right above "E".

People's expectations regarding the ultra-convenience of refueling
today's internal combustion engines will be nearly impossible to change.

 

93.6 at the station around the corner this afternoon.

 

Both I and a friend of mine in highschool drove BMC Minis. I was 6'1"
and Frankie was 6'5".
Mine had thinshell fiberglass buckets set 3 or 4 inches back -
leaving the same rear seat space as the stock seat in the stock
location.
Frank's was stock.

 

No, 55 was introduced for energy savings. It was only later that
a coorelation with lower accidents was noticed - and used by a
lot of people to continue the 55 mph limit.

However, studies on the accident rates were not repeated at
regular intervals to see if other factors would have made any
difference - and when the 55 limit was raised accident rates
didn't rise - due to these other factors becoming a lot more
important over the years than just the speed traveled.

Ted

 

No, Bill, I'm not trying to make up a law of physics here. I'm made an
observation that there IS a sweet spot. I'm not saying the sweet spot
exists because of an inherent law of physics. But, it does exist.

Note also that if you look into this, there are two drag calculations -
linear drag and quadratic drag. The quadratic drag is the doubling of speed
force quadruples which people have been throwing around. Linear
drag is force of drag is proportional to velocity. The linear drag formula
is used for low velocity, the quadratic is used for high velocity. For
a vehicle accellerating from 0, it would fall under the linear formula until
reaching a certain speed then fall under the quadratic formula.

Beyond that, not being a mathmetician, I'll let others speculate. But,
I observed a sweet spot, the EPA observed a sweet spot when they
were studying mileages back in the 70's. It exists.

I suspect the sweet spot in mileage is there simply because any given
type of car engine has a sweet spot on the power curve - there is a
section where with a given engine when you take a certain amount of
power out of it, the engine runs most efficiently. Thus, given any
vehicle you can measure it's drag and as speed increases see how
drag increases - and at the point at which the energy to move the
vehicle through the air is equal to the sweet spot on the power curve,
well there you have your most fuel efficient speed to run the car.

In the early 70's it probably came out at 55 because most cars were
V8's running low RPMs. No guessing in the higher rev 4 bangers that
are most common what it would be nowadays. Might even be 90Mph.

Yes, but when talking governmental regulations we have to look at the
average.

Then, answer this - at what speed does a car stop obeying the linear
drag equation and start obeying the quadratic drag equation?

Ted

 

Then bikes should all go 110Mph so the riders can notice everything
the most. You sound like a damn Harley rider with one of those full
body farings. Yick.

Ted

 

Good question - I will research that. I bet it depends on shape - I
don't know that for a fact, but I suspect it's true. Again - look at
airplanes that travel at quite a bit more than 55 mph and don't hit any
almost impenatrable (sp?) speed wall without additional laws of physics
clearly having to be taken into account (speed of sound notwithstanding).

But whatever the answer is, there are two things staring you in the face:
(1) Your own words: "I suspect the sweet spot in mileage is there simply
because any given type of car engine has a sweet spot on the power curve
- there is a section where with a given engine when you take a certain
amount of power out of it, the engine runs most efficiently. Thus,
given any vehicle you can measure it's drag and as speed increases see
how drag increases - and at the point at which the energy to move the
vehicle through the air is equal to the sweet spot on the power curve,
well there you have your most fuel efficient speed to run the car."

Neither the engine or gearing are fixed, and the body slip-thru-air
properties are also design dependent.

(2) Different cars clearly show different sweet spots as proven by
instantaneous readouts (which though maybe not absolutely accurate are
monotonic - i.e., relative readings can be trusted as far as "more" and
"less").

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')