Most effiecient speed

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Is 55 mph the most fuel economical cruising speed on an '02 Taurus Duratec? Or maybe its higher than that like 65 or so because of engine geering. Well, what is it?

East-
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snipped-for-privacy@yahoo.com wrote:

The MOST efficient speed is the speed of the traffic in the slowest lane.. and keeping it steady.
That is, unless you dont give a flyin' ____ about other people's mileage efficiency, or your or your passengers' nerves, and your time is worth nothing to you.
--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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There is, in the grand scheme of things, no "most fuel efficient speed". Especially given that the conventional, gasoline powered, Otto-cycle engine is far from efficient.
As far as increasing speeds... the drag co-efficient increases exponentially... meaning the faster you go, the harder it is to go faster.
Operating any car will have us spending the most time in part throttle operations.... cylinder filling will be incomplete and pumping losses will be incurred.
FWIW... operating in overdrive (or the highest gear available) at roughly the rpm where peak torque is developed *should* net the best possible fuel mileage.
Lastly, an observation... your last statement comes across too much like a demand..... If you want to demand things, you'll have to pay us more....

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My guess is it depends on the RPMs at which a particular cars torque and HP ratings are attained. Two of my cars have fuel computers, that indicates the fuel mileage as one drives. Both of them show the highest average mileage at around 65 MPH and 2,000 RPMs. At 55 it is around 4 MPG less, curious ay?
mike hunt

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No. Which is why I say again i dont like using OD when cruising at 45 mph.
What i would like to ask Yeastwardbound is what speed he believes is proper to merge into freeway traffic.
I would bet he thinks it's a good idea to merge at 55. And make OTHER people use up THEIR fuel to adjust to him.
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Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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On Sun, 19 Mar 2006 20:18:46 -0500, "Mike Hunter"

Had a '75 Celica GT 5 speed - absolute best fuel mileage was at something like78MPH - 2400RPM in 5th where it did an honest 50MPG Canadian (40MPG American) if held steady - no accellerating to pass, or backing off (Waterloo to Peterborough Ontario at 2AM - 1980 on the way to the Tall Pines Rally.) At 55MPH 30 MPG was stretching it.

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HP
I suspect either your fuel computers are imperfect, or the driving conditions are not truly comparable. It is very unlikely that your vehicles (assuming they are stock) get better fuel economy at 65 than at 55. The power required to overcome drag at 65 mph is around 50% greater than at 55 mph. For production vehicles the bsfc is pretty flat over the normal operating range, and the difference in bfsc between 55 and 65 will be trivial (this is often not true for highly tuned engines, but I assume yours are stock).
I have a lot of experience with Ford fuel computers, and they are not particularly accurate. What technique are you using to determine the 5 mph average and the 65 mph average? When I do that, I usually press the reset button and try to drive at a steady speed for at least 10 miles. This is pretty hard to do at 55 mph, at least in my area. The roads with 55 mph speed limits are usually not conducive to maintaining a steady speed. On the other hand, maintaining a steady 65 is a snap. I have run the same roads at both a steady 55 and a steady 65 and gotten exactly the results you would expect from the fuel computer, - better mileage at 55 than at 65. A few years back, the EPA conducted similar tests, and only one vehicle got better mileage at 65 than at 60 (a 1997 Toyota Celica), and that vehicle got better mileage at both 50 and 60 than at 55. See http://cta.ornl.gov/data/tedb24/Edition24_Chapter04.pdf .
Ed http://home.earthlink.net/~cewhite3/sitebuildercontent/sitebuilderfiles/expmpgcacl3.xls
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You are free to believe whatever you wish.. Try driving with cruse control over the same roads day after day. ;)
mike hunt

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Jim Warman wrote:

Peak torque on my Taurus is at 3250 rpm, in OD that would put me at about 98 mph...
Rob
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I dont think he REALLY meant PEAK torque, rather the shoulder of the curve... but then, you knew that didnt you.. ;)
--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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OK Backyard, you started this assault on Jim, so here is a bit more:
In fact, neglecting turbulence and some other 'nonlinear' effects, the drag coefficient changes very little until you get pretty close to the speed of sound. What changes is the drag force, which is proportional to velocity squared. And, as basic physics teaches, power is force times velocity, which makes it proportional to velocity cubed. Not quite exponential, but still rising pretty fast, multiplying by a factor of eight each time velocity doubles. Playing a bit with numbers for a typical passenger car (Cd=0.4, cross section of 2.5 sq meters), I get about 4hp at 40mph, 13hp at 60mph, and 43hp for those maniacs that zoom by me at 90mph on my daily commute. Add another 44hp that's needed to move 3000lbs up a 6% incline at this speed, and you can see where their money is going.
OK, now we'll probably hear from an aeronautic engineer ridiculing my naive messing with aerodynamics... As long as we are all having fun...
> Jim Warman wrote:

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Hey... no I didnt 'assault' Jim. Let's keep this straight.
--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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And let's keep something in mind, here... same as I first posted: The 'most efficient' or economical speed has nothing to do with it. It's the 'proper social speed' that counts.
Bear in mind:
When speed limit was raised again after the 70's "55, stay alive" debacle, the road accident and fatality rate went down... why? Because drivers were more alert and werent falling asleep.
If you go by simply "most efficient", it's obvious that the lower the speed (given the car is geared to match) the greater the efficiency.. thus why not just set the speed limit at, say, 35 mph?
Well, that's not just boring as hell... it's bad engineering. Because one factor that SO-CALLED safety experts ignore is FLOW DYNAMICS!
Case in point: Around Columbus' beltway there's a stretch of heavily traveled freeway.... cops used to get on TV news and mouth the crap that drivers should 'slow down and leave plenty of distance from car in front'
now assume that at any given time in rush hour there are 500 cars traveling through in a 5 mile stretch between ramps A and B, at the same moment there are 50 cars, per minute, getting on at A and 50 getting off, per minute, at B. If the speed traveled is 60 mph.. the load on the freeway between the points is about 750 cars.
If the speed limit is changed to 30 MPH, you have the same 500 cars going through and the same 50 cars getting on and off, but each of those 50 getting on is staying on twice as long. Thus at any given time, you now have 1000 cars in that stretch between A and B.
The 'experts' will say that's just fine because at 30 it takes less time and distance to stop but that's where the boredom factor comes in... to say nothing of overconfidence. i dont think anyone will dispute that most accidents happen at low speeds and are caused by inattention.
Summary: Drive wide awake, pay attention and blend in with traffic... do not pick the highway as a medium to expose your anti-social behavior.
--
Yeh, I'm a Krusty old Geezer, putting up with my 'smartass' is the price
you pay..DEAL with it!
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Backyard Mechanic wrote:

Hey BY, I agree with your post mainly. It's late so my attention span is short and i bypass longer posts. Most efficient doesn't always mean slower. In a recent RT around OHIO with my car running at it's peak (84 Mark VII, fresh tune up and fluid change, etc) I averaged 24mpg fot the 496 mile round trip at avg 68mph. The trip computer was within .5 mpg average so I trust it's instant readings within 3-4 mpg. At 35 mph, my instant mpg is 18mpg (steady throttle for a distance). Playing with the tripminder, it seems that the ol' Mark gets peak MPG at 63MPH under steady throttle. Under 45 it drops out of OD at light throttle killing the mileage. 35mph steady nets apparently 14mph on that particular car.
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http://www.vtpi.org/tdm/tdm96.htm
Different levels of efficiency, from vehicle miles per hour to vehicles per hour per lane, at different acceptable accident rates.
"A vehicle's road space requirements increase with speed, because drivers must leave more _shy_distance_ between their vehicle and other objects on or beside the roadway. Traffic flow (the number of vehicles that can travel on a road over a particular time period) tends to be maximized at 30-55 mph on highways with no intersections, and at even lower speeds on arterials with signalized intersections."
30-55? That's really defining _it_ for us ;-)
I remembered the "shy distance" from one of the magazines, years ago. I thought the peak efficiency was 45mph on the freeway.
I agree with your boredom factor. A freeway designed for 80 should be boring at 55.
--
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Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8,-122.5
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On Tue, 21 Mar 2006 16:47:08 +0000 (UTC), snipped-for-privacy@XReXXMostX.usenet.us.com wrote:

Well, I just did a couple of tests this morning on my 3.8 liter Pontiac Trans Sport. I ran each test 3 times, on the same stretch of road, which is about a 15 degree incline. I had a roughly 4mph tail wind.
I ran the route at 30, 50, and 74 mph, with the van in overdrive for each run. AIR consumption as measured by the Mass Airflow Meter was 1.56kg/minute at 30mph, 1.98 kg/minute at 50mph, and 2.2kg/minute at 75mph.
At 30mph, which is 1/2 mile/minute, that is 3.12kg/mile or 6.86 lb per mile. At 50mph, which is 5/6 (.83) mile/minute, that is 2.38 kg/mile or 5.23 lb/mile At 75 mph, which is 1.23 miles/minute, that is 1.78 kg/mile or 3.92 lb/mile
At 14:1 afr by weight, that is .0714X6.86=0..499 lb of fuel per mile at 30mph. It is .0714*5.23=.373 lb per mile at 50mph, and .0714X3.92=.2798 lb of fuel per mile at 75mph. Gasoline weighs, lets say, 6 lb per (American) gallon, or 1 lb of gas is .166 gallon.
So this car burned, theoretically,.166X..499=.082 gallons per mile at 30mph, and .166X.373= .062 gallons per mile at 50mph. It burned .166X.2798=.046 gallons per mile at 75MPH.
That is 12.2MPG, more or less, at 30mph, steady state. That is 16.13 MPG at 50MPH steady state, and 21.7MPG at 75MPH steady state.
This is more or less in line with my experience driving on the road, where I can get 700km, or 434 miles on a tank in steady 75mph highway cruising ( which is 21.7MPG, and only 300km or so (186 miles) around town, which is 9.3MPG, and 435-450km on a tank at 50-55mph on local highways. 450km is 280 miles, on 20 US gallons, is 14MPG
Granted, the town mileage is FAR from steady state, so my actual mileage is worse than the theoretical mileage in my test. (only 9.3 instead of 12.2. Knocking around on the back highways at roughly 55 Mph is also not steady state, but I'm only getting about 2mpg less than the theoretical. On the highway, I don't run 75 all the time either - I generally drive 115Kph, and occaisionally as fast as 130 - but to get 700km per tank I generally run 115-125kph, and the average and estimated from the test come out right on the money.
On one tank of gas going to Lakeland Florida one April I went 356 miles, or 574km on 14 US gallons - which is, I believe the best I've done - 25.4 miles per US gallon (31MPG canadian). Average for the entire trip down was better than 22MPG american on a 1700 mile trip.
On the way back, though ice, rain, snow and high winds, we averaged little better than 10mpg. We also had a failed O2 sensor on the way home, making the engine think it was running lean all the time, which made it run PIG RICH.

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On Tue, 21 Mar 2006 13:27:38 -0500, clare at snyder.on.ca wrote:

Just to add to this, the total frontal area of this van is just under 25 sq ft, and the bublished cD I believe is .34 Tractive force requirement is calculated as DaXArew in Sq Ft X (mph)^2/391
So, at 30MPH,.34X25X(30X30)v50/391.56 lbs. At 50MPH, it is .34X25X(50X50)!250/391T.34 lbs. At 75MPH it is .34X25X(75X75)G812/3912.3 lbs
On a 20% grade (just under 12 degrees inclination) it requires.196* vehiclw weight to climb the hill. With a 3600 lb curb weight, that adds 705 lbs of required thrust. Carrying 200 lbs of "stuff" in the van adds 39 lbs of thrust requirement on a 20% grade, which is more than the aerodynamic drag at 30MPH. 400 lbs of passengers/luggage requires more extra power than the difference in speed from 50 to 75MPH. This is totally disregarding the increase in ROLLING resistance due to added weight. Rolling resistance of a radial tire does not change much with speed,(from 0-30mph, virtually the same, then starts to rize - if .012 at 0-20mph, it gets up to about .013 at 60, and .0137 at 70.) but does change with tire inflation, temperature and load. At speed your tires are warmed up, and the pressure is roughly 5PSI higher than at low speed. For every 20% of the rated load on the rire, the rolling resistance co-efficient goes up about .010. Warming up the tire can reduce the rolling co-efficient by 50% (after about 20 miles of driving) and tire pressures. Dropping tire pressure to half the rated pressure DOUBLES the rolling resistance, and increasing beyond recommended pressure by 50% only lowers the resistance about 20%. Having steering geometry out of spec can cost you as much as underinflated tires.
I got all of this information in manuals from Paul Shipps at 3E vehicles to calculate power requirements for my electric car when I built it over 20 years ago. *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com ***
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You were doing 74mph on a 15 deg (27%) incline???? In a car??? ... But heck, what do I know about the Pontiac Trans Sport? Perhaps it can reach 74mph in first gear...
<clare at snyder.on.ca> wrote in message

Trans Sport.

degree incline. I had a

run.
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On Tue, 21 Mar 2006 23:32:24 -0800, "Happy Traveler"

I often run that stretch at 135kph - and I've got a lot of throttle left. Used to do 60 in first with my old Valiant<BG>.

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My 95 T-Bird 4.6 gets its best mpg at 55-60 mph on the interstate. 55mph, tach showing 1,500 rpm = 29 mpg
Steve
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