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Author Topic: 55 MPH vs. 65 MPH Back to Topics
AustinLee3

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Tennessee

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Message Posted: Dec 14, 2013 12:58:24 PM

According to different sites, the more you go over 55 miles per hour, the less gas mileage your car will be getting. Does this apply to all vehicles?

I drive a 2003 Cavalier automatic and its estimates get about 21 city to 30 highway. I've been getting 26 city and 32 highway. I've noticed that when I would normally do 55 miles per hour that my car was getting about 30 miles to the gallon, but when I started doing 65 miles per hour on my normal route to school, I've been getting about 32 - 34 miles to the gallon.

To me, it seems as if my car gets better gas mileage when I'm doing 65 miles an hour. Yes, it's wrong and unsafe to speed, but it's just something that I have noticed.
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hoopitup2000
Champion Author Virginia

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Message Posted: Jul 25, 2014 6:29:55 AM

No carpooler today, so forced me into the slower traffic lanes this morning. Usual commute around 65-70 MPH in the HOV yields upper 40's MPG. Today between 55-60 MPH in non HOV lanes averaged 53.4 MPG. So yes, in my car closer to 55 does increase MPG.
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dontuknowOH
Champion Author Ohio

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Message Posted: Jul 24, 2014 11:05:05 PM

Older vehicles that had larger engine displacement and were the V-type configuration had more torque power at the lower range of the total power band.

The shorter stroke higher revving powerful 4 cylinder engines with better ECM control DOHC and variable cam timing can cruise at a higher travel speed which is in harmony with the torque/HP. makes a switch a rue to keep engine energy levels proper for the newer multi speed tranny gearing changes

When torque drops off, HP still starts to deliver at the upper band range, when the trannies are in a lower gearing (downshift) or winding out the upper RPMs under heavier tall gearing loads.

The trannies let the torque increase at the transmission's output drive line delivered then to the drive wheels, then Performance is gained back and a bit of economy also in a lighter weight vehicle containing a much smaller size engine. It takes a total package of newer innovations combined to bring the economy back in order for cruise travel.

There are still bounds between travel speeds of different engine types/sizes/application. Bounds of finding the harmony best speed of each vehicle for cruise travel concerning fuel mileage/cost.
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Vin63
Champion Author San Bernardino

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Message Posted: Jul 23, 2014 9:51:27 AM

It depends on your vehicle and its coefficient of drag.
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51stovi
All-Star Author Nashville

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Message Posted: Jul 23, 2014 9:36:58 AM

Don't drive less than the speed limit. It's a safety issue and annoying!
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93XtraCab
Rookie Author Maryland

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Message Posted: Jul 22, 2014 12:56:10 PM

My truck is geared high because it is underpowered, so at 65 mph, it is screaming, so I stay off the freeways. 55 mph is much better for me.
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MertieMan
Champion Author Lexington

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Message Posted: Jul 21, 2014 9:30:44 AM

You can't go out onto the interstates and drive these slow speeds unless you want to be killed.
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kingstorey
Rookie Author Grand Rapids

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Message Posted: Jul 21, 2014 4:32:22 AM

There is a difference
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fcdriver
Champion Author Tennessee

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Message Posted: Jul 21, 2014 4:05:13 AM

most people go much faster then that
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WilhamClouse
Champion Author Calgary

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Message Posted: Jul 20, 2014 3:21:55 PM

75+
I prefer the faster speed over any fuel savings.

[Edited by: WilhamClouse at 7/20/2014 3:22:27 PM EST]
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Vin63
Champion Author San Bernardino

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Message Posted: Jul 18, 2014 9:46:16 AM

It depends on your vehicle's gearing and coefficient of drag.
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sanderstheparro
Champion Author Wilmington

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Message Posted: Jul 18, 2014 9:30:40 AM

Generally, the faster you drive, the poorer your fuel economy.

As for 55 MPH vs. 65 MPH, it depends on the number of gears you have, aerodynamics and weight of the vehicle. Every vehicle has a sweet spot where they get the maximum miles per gallon whether at 55 or 65 mph. But generally, if you go beyond your sweet spot, your mileage economy begins to suffer greatly.
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MertieMan
Champion Author Lexington

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Message Posted: Jul 18, 2014 8:08:47 AM

Drive these speeds on the interstates and get run over, especially I-75 southbound.
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GBMAX
Champion Author Phoenix

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Message Posted: Jul 9, 2014 10:44:54 PM

64 - 67
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dontuknowOH
Champion Author Ohio

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Message Posted: Jul 9, 2014 7:05:54 PM

The big difference in engine design controls has made a big difference in how the power band of todays vehicles handle different road conditions/speed choices.

Older vehicle engines had distributors/timing devices that could get out of tune along with aging/engine wear/mileage build-up.

The modern engines have systems that stay in tune and can adjust energy performance as they are driven. Coil packs, EFI, variable cam timing, many sensors to monitor engine duties along with electric controlled automatic transmissions creates better mileage all done automatically.

Simply the engine can deliver more energy at the higher road speeds because of these refined systems(complexity)V/S the older design vehicles of "60's"...."mid "90's". Along with energy is better mileage with less HP.using(smaller engine size) One can look at the degree of windshield slope on the economy vehicles and tell that, even the front grill mass is less.

Much more all equals higher travel speed against the elements of physics(the planet Earth's resistive forces)with less fuel energy involved. Compare to the "Stagecoach days" Those engines had to be fed/watered 24-7!
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Boyrr
Champion Author Allentown

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Message Posted: Jul 9, 2014 6:40:05 AM

it all depends on the overall design, what gear ratios, ect.
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herbiepopnecker
Champion Author British Columbia

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Message Posted: Jul 9, 2014 1:59:41 AM

Yeah right, what's settled is exactly what speed the EPA set to determine highway mileage which is likely to still be stuck at the old double nickel.
They don't make an American car geared to deliver best mileage over 55-60. Experiment all you want, you'll find out fast enough.
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WilhamClouse
Champion Author Calgary

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Message Posted: Jul 8, 2014 1:02:39 PM

don't really care....I go 75 mph+

[Edited by: WilhamClouse at 7/8/2014 1:03:04 PM EST]
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GrumpyCat
Champion Author Alabama

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Message Posted: Jul 7, 2014 12:57:14 PM

"I've never calculated it but I'm sure the mpg. will go down above 60 mph. I will not drive over 70 mph. anywhere."

Thats what we call "Settled Science". "I'm so smart and know everything that I don't even have to experiment or measure. I know what the results will be."

The problem is that its not science if its "settled." Any "scientist" who is not aware of how many times "settled science" has been turned on its ear and proven wrong is not a scientist worth his salt.

As I have posted previously my 2000 Avalon XLS did better at 70 MPH than at 60 MPH. 2009 ML320BT gets 31 MPG at 60 or 29 at 70. 2001 Sonoma 2.2L 5-speed could get 27 at 60 MPH, or 20 at 70 MPH. Am told the V6 model got better MPG at 70 than my I4 model, but worse than the I4 at 60 MPH.

My point being its not settled science. You have to measure.
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46chief
Champion Author Indiana

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Message Posted: Jul 7, 2014 10:45:21 AM

I've never calculated it but I'm sure the mpg. will go down above 60 mph. I will not drive over 70 mph. anywhere.
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Floridaman2013
Champion Author Atlanta

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Message Posted: Jul 7, 2014 8:42:53 AM

My truck is around 65 and the Grand Cherokee is 70-72 mph. So many variables involved as every vehicles, situation is different. Going 55 was for the the cars of the '70 after the Arab oil embargo as most were not fuel efficient as today. That speed is actually to low by today's standards, unless you are driving an older vehicle.
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Madridjoe
Veteran Author Lancaster

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Message Posted: Jul 7, 2014 6:36:48 AM

for me, it will start to drop off above 60
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cv
Champion Author Raleigh

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Message Posted: Jul 7, 2014 6:15:45 AM

My peak gas mileage seems to be around 60mph.
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dontuknowOH
Champion Author Ohio

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Message Posted: Jul 6, 2014 5:32:26 AM

A faulty MAF sensor or dirty one can drop engine power or a low compression cylinder getting a bit dirty effects the 02 sensors cutting the EFI to lean for good performance drop-off. Even one cyl. sucking too much PCV vapor build-up into the intake runners, often a C Case venting condition getting faulty/partial plugged (sometimes intermittent)problem on hot days.

Variance in older designed vehicles V/S todays are different because of better technology for OEM drive-line gearing, mainly the modern automatic transmissions, electric controlled (ECM systems).
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GrumpyCat
Champion Author Alabama

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Message Posted: Jul 5, 2014 11:26:33 AM

"The main thing I notice is at 55 MPH highway the tranny down-shifts from O-Drive on hotter/drier days on some hills. Driving at the 72 MPH. speed on days of 70F* and less, same hills no down-shifts even with E-10 in the fuel."

I had a 2001 GMC Sonoma 2.2L 5-speed. One particular hill was easy to climb in 5th at 65 MPH (posted limit) but at 55 MPH the engine was floored and straining, or spinning its heart out in 4th.

With A/C off the Sonoma obeyed the "everybody (thinks they) know(s)" laws of MPG. 50 MPH was 30 MPG, 55-60 MPH was 25-27 MPG. 70 MPH was 21 MPG. A/C cost 2.5 MPG.

My 2000 Avalon got 30+ MPG at 67-72 MPH and less than 27 MPG at 60 MPH.

[Edited by: GrumpyCat at 7/5/2014 11:27:16 AM EST]
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dontuknowOH
Champion Author Ohio

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Message Posted: Jul 4, 2014 8:21:22 AM

My daily driver of 14 years has a power band that lets it gain speed, much quicker from 72-80+ without down-shifting from O-Drive gearing.
Quicker than it does from 60-70 MPH.in top gearing O-Drive.

That ability using the E-10 nowdays is a bit diminished, of course the vehicle has aged, and different tires are employed. Nearing 80K miles the vehicle has had only one mechanical tune-up, and I recently had to replace it's last 2nd. battery after 7.5 years (good service) by my standards.

The main thing I notice is at 55 MPH highway the tranny down-shifts from O-Drive on hotter/drier days on some hills. Driving at the 72 MPH. speed on days of 70F* and less, same hills no down-shifts even with E-10 in the fuel.

I'm assuming my mid-range torque peak runs out and then the HP. upper range grows in building more engine power at the higher road speeds.

Either way more fuel gets used by opening the throttle(Go-Pedal) toward the 85% mark, whatever... cruise on/off.
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MertieMan
Champion Author Lexington

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Message Posted: Jul 4, 2014 7:44:48 AM

Who cares, just drive the pea pickin car and don't worry about it.
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Skyjunky
All-Star Author Portland

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Message Posted: Jul 3, 2014 11:46:57 PM

55mph is about the best for me.
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GrumpyCat
Champion Author Alabama

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Message Posted: Jul 3, 2014 10:59:29 PM

Another datapoint: I recently drove my SUV on the previously cited 1000 mile round trip (500 miles each of 2 days) at 60 MPH. Got 31 MPG at about 50°F average outside temperature.

Previously at 70°F and hotter at 70 MPH I got 29 MPG.

This winter I did it again at temperatures ranging from 2°F to 40°F at 70 MPH and got 28 MPG. The fool computer indicated terrible MPG the first 100 miles from 2°F. I should have blocked the radiator.

The extra 3+ hours on the road were not worth the $12 ($6/day) saved in fuel. Not to mention the rolling hazard I created driving interstate at 60 MPH.

All MPG numbers cited are calculated based on odometer miles divided by quantity of fuel purchased. No built-in fool computer numbers.
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dontuknowOH
Champion Author Ohio

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Message Posted: Jul 1, 2014 5:34:54 PM

Cruising at 64--67MPH. works for me for best economy. When heavier loaded near 70 MPH. gives better results with my 4 cylinder vehicles. When strong headwinds prevail I drop the average cruise speed to 62 MPH.
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lyanMI
Champion Author Detroit

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Message Posted: Jul 1, 2014 4:45:47 PM

At 65mph I get good mpg
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carinthuist
Champion Author San Francisco

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Message Posted: Jul 1, 2014 2:28:45 PM

60mph
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HotRod10
Champion Author Wyoming

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Message Posted: Jul 1, 2014 12:20:41 PM

"here where i live we can do 70 - 80 mph in some places..."

The 80mph speed limit signs are going up on sections of the interstates in WY starting today.
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ravenous2012
Rookie Author Houston

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Message Posted: Jul 1, 2014 12:00:11 PM

I drive a 2006 Dodge Grand Caravan, and when i do around 60+ it gets better mileage up unto to 70 mph. here where i live we can do 70 - 80 mph in some places...

I also drive 15miles to work and then the same back to home.
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GrumpyCat
Champion Author Alabama

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Message Posted: Jul 1, 2014 11:06:05 AM

"The sweet spot on my 2002 Chevy Silverado 2wd was at 64mph. Every time to Indiana and back would get me 23.4mpg. Same as going to STL and back. Now if I happen to be in a hurry or someone else was driving anything over 65 would bring around 16.8mpg. Driving 55 -60 did was actually less then 21mpg. I record milages and gallons at each fill up and put into my excel spreadsheet and I also bought out of curiosity one of those mpg readers that plug into the vehicles to give me real time info. They were incredibly accurate."

Blasphemer! Denier! Heretic! :-)

How dare you question Settled Science? Those Who Are Smarter Than You Know Better!

I too have driven 20-25 1,000 mile round trips and concluded 67-72 MPH was the sweet spot for a 2000 Avalon XLS. Never less than 30 MPG by calculator, which was over the 29 MPG EPA rating, or the 27 MPG revised EPA rating. Never got more than 27 MPG at 60 MPH.
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davisadm
Champion Author Los Angeles

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Message Posted: Jul 1, 2014 10:45:43 AM

I probably would get better MPGs at 55, but i drive 65+
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coreyparks
Rookie Author Missouri

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Message Posted: Jul 1, 2014 9:34:24 AM

The sweet spot on my 2002 Chevy Silverado 2wd was at 64mph. Every time to Indiana and back would get me 23.4mpg. Same as going to STL and back. Now if I happen to be in a hurry or someone else was driving anything over 65 would bring around 16.8mpg. Driving 55 -60 did was actually less then 21mpg. I record milages and gallons at each fill up and put into my excel spreadsheet and I also bought out of curiosity one of those mpg readers that plug into the vehicles to give me real time info. They were incredibly accurate.
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dassfg
Champion Author Fort Worth

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Message Posted: Jul 1, 2014 7:55:48 AM

If your car has a tach & fuel economy meter you can find the sweet spot where it gets the best fuel economy. This spot in the torque curve is where your car will perform best in whatever gear you are in. Some cars actually get better fuel economy at 65 than they do at 55.
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WES03
Champion Author Maryland

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Message Posted: Jul 1, 2014 7:50:23 AM

I definitely get better mileage at 55 vs 65+.
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dontuknowOH
Champion Author Ohio

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Message Posted: Jun 20, 2014 2:00:17 AM

My thoughts are; If every driver/vehicle went travel faster all around/across this world, more oxygen would need to be used up mainly by machines. When large forest fires consume vast amounts along with more population of vehicles, housing, natural explosions/heat, then do we world-wide have enough recovery rate from the remaining natural environment.

Just saying Human minds sort of take oxygen for granted(no concern),where machinery operation requires fuel/air we breath....Tons of air! HMmmmm.....
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twt
Champion Author Virginia Beach

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Message Posted: Jun 17, 2014 5:46:06 AM

Yes, it applies to all gasoline powered vehicles.
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HotRod10
Champion Author Wyoming

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Message Posted: Jun 16, 2014 6:03:11 PM

"I think the real question we have to ask is why are cars not set for a higher speed?"

There's only so much that can be done with gear ratios and timing adjustments. To the extent possible, I believe those optimizations have been incorporated into the engine and drivetrain design in newer vehicles. The other major, but less predictable, factor is the wind resistance, which is highly variable based on things as minor as whether the vehicle is clean or dirty (and depending on the speed, humidity, air density, etc. clean is not necessarily better).
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Mikeyl
Champion Author Cleveland

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Message Posted: Jun 16, 2014 5:42:46 PM

I think the real question we have to ask is why are cars not set for a higher speed? Most states are now at least 60 MPH. In Ohio, most rural areas and the Turnpike are 70 MPH.

So, can be adjust the timing so we get better gas milage at 65 MPG?
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mnrick041
Champion Author Twin Cities

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Message Posted: Jun 11, 2014 9:19:22 PM

It really depends on the car. Things like the engine and the transmission vary from car to car and different cars will get better MPG's at different speeds.
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Alcoman
Champion Author Albany

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Message Posted: Jun 11, 2014 8:18:11 PM

I have a 2013 Dodge Dart that got 43.9 mpg hand calculated at 65 mph.
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RS101
Champion Author Minnesota

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Message Posted: Jun 11, 2014 4:58:32 AM

approx 65 but it also depends upon other factor including tire pressure, windows open/closed, etc.
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krazkar
Champion Author Calgary

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Message Posted: Jun 11, 2014 12:12:24 AM

Speed limits are too low
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Houckster
Champion Author Atlanta

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Message Posted: Jun 10, 2014 3:32:09 PM

Find out how much fuel you lose at 70 vs 60.
More evidence that speed kills MPG
Wikipedia: Fuel Economy in Automobiles

[Edited by: Houckster at 6/10/2014 3:38:51 PM EST]
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Jackson126
Veteran Author Virginia

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Message Posted: Jun 10, 2014 2:42:17 PM

I believe my car gets better mileage at 65-70.
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shstew
All-Star Author British Columbia

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Message Posted: Jun 10, 2014 10:58:35 AM

I drive the speed limit
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badbobKY
Sophomore Author Lexington

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Message Posted: Jun 10, 2014 10:33:50 AM

65
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