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

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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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dontuknowOH
Champion Author Ohio

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Message Posted: Aug 19, 2014 9:40:20 PM

Since I don't own an electric vehicle at present I will have to confer with my chat friends then relying on their reports over time. The thing is I have difficulty with their facts V/S their owner opinions, they are hard to satisfy.

Older guys just stick to their main likes, and that makes it really hard to even open their reasoning gates. They don't even care about cruising speeds, none of the three think the same about that.

When you have several opinions doing comparisons, one ends up with much different data, then there is that natures wind factor to upset those factors, data whatever, logical reality....... Again! Wind direction......is a factor!.......
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Awing1
All-Star Author Ontario

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Message Posted: Aug 19, 2014 3:19:01 PM

It's a general description that you can get better mileage up to certain speed than higher speeds, but it also depends on cars due to different gears, etc. For me, 55 or 65 mph doesn't have big difference.
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GrumpyCat
Champion Author Alabama

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Message Posted: Aug 19, 2014 2:59:38 PM

"Yes there is no logical way one can compare the modern electric driven vehicles with cruising speed differences(Sweet spots)of economy travel speeds."

Sure there is a logical way to compare. Fuel up, drive, measure. Nothing has changed.

What one can't do is make broad generalizations about vehicles. Thats the same mistake as many fool governments have made in giving preferential treatment to "hybrids". Just because a vehicle is a hybrid doesn't mean it has similar benefits as a Prius.
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dontuknowOH
Champion Author Ohio

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Message Posted: Aug 19, 2014 10:26:17 AM

Yes there is no logical way one can compare the modern electric driven vehicles with cruising speed differences(Sweet spots)of economy travel speeds.

I must hand out gratitude for the newer technology, I just never hear much talk about how good of mileage the electric motivated vehicles are when adverse winter snows, ice, very low degree temps effect those vehicles when in daily use. Wondering if they make a 4X4 hybrid, probably do for the north climates.

I know Winter, bad Winters drive up my driving costs, not owning any Hybrids as yet. Three casual friends have bought new ones this year, three that I have seen, each a different color,...options. Sixty-4-72 MPH. is my Sweet spot on a Summer calm day cruising, level terrain. I buy one size oversize tires when replacing.
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GrumpyCat
Champion Author Alabama

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Message Posted: Aug 18, 2014 10:17:54 AM

"The lower speed of 55 for older vehicles Non ECM or early ECM controlled. The higher speed of 65 + or - works for the OHC VCT ECM controlled including Turbo charged premium gas or diesel with multi speed trannys(CVTs) MYOP….."

That is way way too broad of a generalization.

My Prius had more electronic controls governing the engine and drive than you can shake a stick at. Its peak MPG was at about 38 MPH. Big dip in the low 40's. Another peak about 50 MPH, after which it tapered off as speed increased much as the theorists are broadly claiming for all vehicles.

As I said before my 2000 Avalon XLS peaked at about 67 MPH.

My diesel SUV gets 29 MPG at 70 MPH on the same 500 mile day quoted for the Avalon. 31 MPG if driven at 60 MPH. Prius got 43-45 MPG on same 70 MPH route.
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WES03
Champion Author Maryland

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Message Posted: Aug 18, 2014 9:32:17 AM

I notice a fall off in MPG when driving at 65-70 MPH.
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Jackson126
Veteran Author Virginia

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Message Posted: Aug 17, 2014 9:31:26 AM

No depends on gearing and engine output
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dontuknowOH
Champion Author Ohio

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Message Posted: Aug 17, 2014 8:25:36 AM

The lower speed of 55 for older vehicles Non ECM or early ECM controlled. The higher speed of 65 + or - works for the OHC VCT ECM controlled including Turbo charged premium gas or diesel with multi speed trannys(CVTs) MYOP.....
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davisadm
Champion Author Los Angeles

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Message Posted: Aug 16, 2014 11:57:32 AM

It depends how a cars gearing is set up and at what speed the engine is turning at the most efficient RPM.
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BUSSY
Champion Author Dallas

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Message Posted: Aug 16, 2014 11:44:30 AM

I think 55MPH would apply to most for best mileage
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Banjoe
Champion Author Winnipeg

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Message Posted: Aug 16, 2014 9:52:55 AM

GrumpyCat - a perfect example of seeking out the sweet spot specific for each vehicle.

There is no global answer that covers all situations and it takes work to discover each individual case.
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GrumpyCat
Champion Author Alabama

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Message Posted: Aug 13, 2014 3:35:29 PM

"If some vehicles have higher gears for going faster, it's possible that they'd be getting their best mileage at a higher speed. However, no American made cars or trucks fall into this category."

I have logged over 20,000 miles on interstate in a Kentucky-built 2000 Toyota Avalon XLS which got its best MPG at about 67 MPH.

On 70 MPH roads I never got less than 30 MPG. Typically on 500 mile days.

On 60 MPH roads I never got over 27 MPG.

All MPG calculated at fuel pump with calculator and logbook.

[Edited by: GrumpyCat at 8/13/2014 3:36:01 PM EST]
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Banjoe
Champion Author Winnipeg

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Message Posted: Aug 13, 2014 8:16:42 AM

Can't support your point because we certainly don't get the best mileage standing still.

There's a lot that goes into the final number besides drag so let's not get focused on only one factor in the chain.
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46chief
Champion Author Indiana

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Message Posted: Aug 9, 2014 8:58:23 AM

As you double your speed the drag co-efficient on your vehicle quadruples. More drag means more gas.
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OilerFan
Champion Author Tulsa

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Message Posted: Aug 9, 2014 8:58:04 AM

Every vehicle I've ever driven, the gas mileage was worse as the speed increased. Essentially, the harder the engine works, the lower the mileage. If the RPMs are higher, it's working harder.
The transmission basically allows a comfortable drive at 55, and the RPMs are reasonably at a relaxed rate. Anything higher means the engine is working harder and getting fewer mileages per gallon. That's just basic.
If some vehicles have higher gears for going faster, it's possible that they'd be getting their best mileage at a higher speed. However, no American made cars or trucks fall into this category.
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Banjoe
Champion Author Winnipeg

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Message Posted: Aug 9, 2014 7:26:05 AM

Don't mean to rain on anyone's parade but faster doesn't mean more fuel consumption.

Slow speeds are a killer on my diesel mileage and it's not happy until it's in 6th gear and in the 55 - 65 mph range.
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twt
Champion Author Virginia Beach

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Message Posted: Aug 9, 2014 4:14:06 AM

Of course, it burns more gas when driving faster. If the engine is running faster, it's using more fuel. DUH
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krazkar
Champion Author Calgary

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Message Posted: Aug 9, 2014 12:43:32 AM

Don't care, rather drive faster.
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dontuknowOH
Champion Author Ohio

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Message Posted: Aug 8, 2014 9:48:24 AM

I must agree with MertieMan , Way too much operational junk in the modern vehicles along with Many Drivers don't seem to know what Assured Clear distance is anymore or Mainly even Don't Care! Nerves V/S Risky..... seems so..... Vehicle Playtime.... Say What?.... Weather conditions....? Yey-Ok!
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MertieMan
Champion Author Lexington

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Message Posted: Aug 8, 2014 9:06:33 AM

You positively can't drive speeds like this on the interstates, unless of course you have a "death wish".
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drivebye
Veteran Author San Jose

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Message Posted: Aug 8, 2014 1:01:05 AM

In the last few days I've read news articles on GasBuddy that indicate speed limits are rising in some states due to results of latest research.

In 2014, four states have raised posted limits to as high as 80 mph or else they added more roads to the maximum limits. On the other hand, there have been other states that tried to raise speed limits this year but failed.

Here's more info: www.iihs.org/iihs/sr/statusreport/article/49/6/3
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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
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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
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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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