Fuel economy myths

"Bill Putney" <bptn@kinez.net> wrote in message
news:5ms9i4Ff6kgbU1@mid....
> Ted Mittelstaedt wrote:
> > "Bill Putney" <bptn@kinez.net> wrote in message
> > news:5mpbqtFepcpsU1@mid....
>
> >>Which is the cause and which is the effect? Are official mileage
> >>figures done at 55 mph because that is a fixed law of physics that that
> >>is the optimum (fuel mileage) speed for a wheeled vehicle.
> >
> >
> > Actually Bill I think that 55mph really is the "sweet spot" for a
NON-wind
> > optimized
> > vehicle.
> >
> > I ride a motorcycle quite frequently that has NO faring (Honda CB750 if
> > anyone cares)
> > with an upright riding posture. (it's the most comfortable)
> >
> > I can feel force on my arms increase as speed increases. However, it is
NOT
> > linear. Up until about 55 you can barely feel it. The faster I go
beyond
> > this the
> > force really does build up very quickly, even going an additional 5 Mph.
> > Normally
> > I cruise at 65-70. Other bikers in the M/C forums have noted the same
> > thing.
>
> 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.
>

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.

> 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.

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

> 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.

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

Ted

Ted Mittelstaedt wrote:

> "Bill Putney" <bptn@kinez.net> wrote in message
> news:5ms9i4Ff6kgbU1@mid....
>
>>Ted Mittelstaedt wrote:
>>
>>>"Bill Putney" <bptn@kinez.net> wrote in message
>>>news:5mpbqtFepcpsU1@mid....
>>
>>>>Which is the cause and which is the effect? Are official mileage
>>>>figures done at 55 mph because that is a fixed law of physics that that
>>>>is the optimum (fuel mileage) speed for a wheeled vehicle.
>>>
>>>
>>>Actually Bill I think that 55mph really is the "sweet spot" for a
>
> NON-wind
>
>>>optimized
>>>vehicle.
>>>
>>>I ride a motorcycle quite frequently that has NO faring (Honda CB750 if
>>>anyone cares)
>>>with an upright riding posture. (it's the most comfortable)
>>>
>>>I can feel force on my arms increase as speed increases. However, it is
>
> NOT
>
>>>linear. Up until about 55 you can barely feel it. The faster I go
>
> beyond
>
>>>this the
>>>force really does build up very quickly, even going an additional 5 Mph.
>>>Normally
>>>I cruise at 65-70. Other bikers in the M/C forums have noted the same
>>>thing.
>>
>>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.
>>
>
>
> 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.
>
>
>>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.
>
>
> Yes, but when talking governmental regulations we have to look at the
> average.
>
>
>> 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.
>
>
> Then, answer this - at what speed does a car stop obeying the linear
> drag equation and start obeying the quadratic drag equation?
>
> 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')

who wrote:
> In article <DsCdnfJ7s86a-JvanZ2dneKdnZydnZ2d@bt.com>,
> Coyoteboy <coyoteboyuk@m> wrote:
>
>> Chevy Man wrote:
>>> Only thing I see that will force higher fuel economy is for gas to get up
>>> to
>>> around $10 a gallon. Most people have not even slowed down at $3.
>> Wont affect anyone anyway - in the uk we pay the equiv of 7.70 a US
>> gallon - people here are still happily ploughing around in 20mpg cars
>> (me included).
> The cars I see in the UK, I travel their every few years, are
> significantly smaller on the average than those in NA, with smaller
> engines.
> In NA a mid sized car needs at least a 2.7L V6 engine to sell.
>
> However in both the UK and NA there seems to be a trend for some people
> to go larger and some to go smaller, so the number of fuel efficient
> cars in the middle is decreasing.
> Here in western Canada over 50% of vehicles are large truck based SUVs
> or tall heavy cross over vehicles with large engines. Neither get good
> urban mileage which is most of the driving.

This is true, we do have an average mpg of around ~35 these days, but
thats not the point really - my point was that even at 770 a gallon it
makes no odds to peoples usage. Everyone moans, everyone complains about
the taxes (its something close to 80% tax in total IIRC) but people
dont change their habits. Sure there are some that get a smaller car,
but most just carry on as before with each increase. Increasing fuel
costs wont bother anyone until it exceeds public transport costs by a
LONG way. Here in the UK I can get a (late,smelly,crowded) train to my
place of work for ~£6 return. Or pay £7 and drive in comfort in a very
low mileage car. You'd have to either make fuel ~$15 a gallon or reduce
the cost of the trains significantly to make any of the majority
reconsider car use.

Coyoteboy wrote:
> who wrote:
>> In article <DsCdnfJ7s86a-JvanZ2dneKdnZydnZ2d@bt.com>,
>> Coyoteboy <coyoteboyuk@m> wrote:
>>
>>> Chevy Man wrote:
>>>> Only thing I see that will force higher fuel economy is for gas to
>>>> get up to around $10 a gallon. Most people have not even slowed down
>>>> at $3.
>>> Wont affect anyone anyway - in the uk we pay the equiv of 7.70 a US
>>> gallon - people here are still happily ploughing around in 20mpg cars
>>> (me included).
>> The cars I see in the UK, I travel their every few years, are
>> significantly smaller on the average than those in NA, with smaller
>> engines. In NA a mid sized car needs at least a 2.7L V6 engine to sell.
>>
>> However in both the UK and NA there seems to be a trend for some
>> people to go larger and some to go smaller, so the number of fuel
>> efficient cars in the middle is decreasing.
>> Here in western Canada over 50% of vehicles are large truck based SUVs
>> or tall heavy cross over vehicles with large engines. Neither get good
>> urban mileage which is most of the driving.
>
> This is true, we do have an average mpg of around ~35 these days, but
> thats not the point really - my point was that even at 770 a gallon it
> makes no odds to peoples usage. Everyone moans, everyone complains about
> the taxes (its something close to 80% tax in total IIRC) but people
> dont change their habits. Sure there are some that get a smaller car,
> but most just carry on as before with each increase. Increasing fuel
> costs wont bother anyone until it exceeds public transport costs by a
> LONG way. Here in the UK I can get a (late,smelly,crowded) train to my
> place of work for ~£6 return. Or pay £7 and drive in comfort in a very
> low mileage car. You'd have to either make fuel ~$15 a gallon or reduce
> the cost of the trains significantly to make any of the majority
> reconsider car use.

How do you figure we have a mileage of 35mpg???

I think fuel mileage isn't getting any better than it was 30 years ago.

In article <470b3ec2$0$14856$9a566e8b@news.aliant.net>,
Picasso <Picasso@> wrote:

> I think fuel mileage isn't getting any better than it was 30 years ago.

It certainly has improved for the larger cars and engines.
I do agree that for smaller cars and engines there has been little
improvement in fuel mileage, but small engine power has increased
significantly.

who wrote:
> In article <470b3ec2$0$14856$9a566e8b@news.aliant.net>,
> Picasso <Picasso@> wrote:
>
>> I think fuel mileage isn't getting any better than it was 30 years ago.
>
> It certainly has improved for the larger cars and engines.
> I do agree that for smaller cars and engines there has been little
> improvement in fuel mileage, but small engine power has increased
> significantly.

So what you're saying is we're really going the wrong way?

Honda Civic...

1985 34mpg
1995 38mpg
1999 30mpg
2007 29mpg
(fueleconomy.gov)

Why would we want to decrease fuel economy, for a only slightly better
working car?

Thats probably only one car though, i don't have time to do others

I would guess pickups have hovered somewhat the same... maybe only
slighly better with smaller efi engines doing the same job and making
more power.

"Picasso" <Picasso@> wrote in message
>
> Honda Civic...
>
> 1985 34mpg
> 1995 38mpg
> 1999 30mpg
> 2007 29mpg
> (fueleconomy.gov)
>
> Why would we want to decrease fuel economy, for a only slightly better
> working car?

But is this really the same car? The name may still be the same, but the
Civic today is closer in size to the Accord of some years ago. We keep
asking for (and getting) larger cars. I'm not sure how many cars you can
directly compare having the same name and being interior size over a 15 year
span. Crown Vic? LeSabre?

Picasso wrote:
> who wrote:
>> In article <470b3ec2$0$14856$9a566e8b@news.aliant.net>,
>> Picasso <Picasso@> wrote:
>>
>>> I think fuel mileage isn't getting any better than it was 30 years ago.
>>
>> It certainly has improved for the larger cars and engines.
>> I do agree that for smaller cars and engines there has been little
>> improvement in fuel mileage, but small engine power has increased
>> significantly.
>
> So what you're saying is we're really going the wrong way?

We're making choices that result in lower fuel mileage.

> Honda Civic...
>
> 1985 34mpg
> 1995 38mpg
> 1999 30mpg
> 2007 29mpg
> (fueleconomy.gov)

Yet there is the new Honda Fit, which is smaller than the Civic and gets
better mileage. And the Civic hybrid, Prius, etc.

> Why would we want to decrease fuel economy, for a only slightly better
> working car?

Larger cars and more power.

> Thats probably only one car though, i don't have time to do others

It's a common trend. You start with a small car. Over time, successive
generations tend to get bigger, more powerful and less fuel efficient.

> I would guess pickups have hovered somewhat the same... maybe only
> slighly better with smaller efi engines doing the same job and making
> more power.

I think pickup trucks have gotton larger over time, with more power, too.

Jeff

Dori A Schmetterling wrote:
> I don't understand the penchant for quoting L/100 km, as is common
> throughout Continental Europe.
>
> Km/l would be much more useful.

Its irrelevant, mpg, l/km and km/l are all equally informative and give
you exactly the same information. Its a matter of personal preference. I
see what youre thinking though.