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Old 10-03-2014, 09:53 AM   #41
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Of course they do. Had they included a Suburban it would probably have been "the best" falling from an (estimated) 20 mpg @ 55 mph to 15 mpg @ 75 mph - a drop of "only" 5 mpg! Percent is the logical way to compare. Note that the highest mpg cars are still the highest at higher mph, and the lowest remain the lowest - isn't that the relevant comparison?
I don't think either measurement is the most relevant.

Seems that most people are focusing on 'how much extra will it cost me to drive at 75 mph versus 55 mph (all else being equal)' - they can then weigh this extra cost versus the time they save.

So if I did my math right (converting mpg to gallons per 100 miles), the largest $ savings is the Mercury Mountaineer, which is in the middle of the pack as far as % delta, but since it is the lowest mpg in the bunch, this translates to the largest dollar savings per 100 miles.

(edit/add: ) Numbers - assuming $3.50/gallon, the Mountaineer will cost you $4.96 extra to travel 100 miles at 75 mph versus 55 mph. In the Yaris, it will cost you $2.06 extra to travel 100 miles at 75 mph versus 55 mph.

And a 100 mile trip will take 1.8181818182 hours at 55 mph, 1.3333333333 hours at 75 mph - a savings of 29.0909090909 minutes (approximately ).

-ERD50
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Old 10-03-2014, 10:04 AM   #42
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I don't think either measurement is the most relevant.

Seems that most people are focusing on 'how much extra will it cost me to drive at 75 mph versus 55 mph (all else being equal)' - they can then weigh this extra cost versus the time they save.

So if I did my math right (converting mpg to gallons per 100 miles), the largest $ savings is the Mercury Mountaineer, which is in the middle of the pack as far as % delta, but since it is the lowest mpg in the bunch, this translates to the largest dollar savings per 100 miles.

-ERD50
And a Suburban or a Humvee would be even "better" even though the total cost would be higher per mile.

"Most people?" I'd guess the person who buys the Honda Insight couldn't care less that he/she would spend incrementally more to drive 75 mph than someone with a Mercury Mountaineer. They're going to spend less on fuel than less efficient vehicles at the same speeds.

And someone with a Suburban doesn't consider MPG a priority. Their prerogative, some people truly need larger vehicles for a variety of reasons.
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Old 10-03-2014, 10:17 AM   #43
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And a Suburban or a Humvee would be even "better" even though the total cost would be higher per mile.

"Most people?" I'd guess the person who buys the Honda Insight couldn't care less that he/she would spend incrementally more to drive 75 mph than someone with a Mercury Mountaineer. They're going to spend less on fuel than less efficient vehicles at the same speeds.

And someone with a Suburban doesn't consider MPG a priority. Their prerogative, some people truly need larger vehicles for a variety of reasons.
As I said 'all else being equal' - I'm thinking along the lines of, I already own the car, what will my trade-off be on this particular trip, with this particular car that I own. Is it 'worth it' to me to spend $x.xx to get there xx minutes early? I believe that was the focus of the OP - can you optimize the trip for the car you own?

To use this information for a new car purchase ( a very different calculation ), I'd be comparing a total cost of ownership based on the weighting of the speeds I typically drive, and maybe even make the decision at that point to keep my highway speeds lower.

Fortunately for me, I don't drive enough to have to do a deep dive into those numbers. A vehicle with 'decent' mpg is good enough for me, I just found this to be an interesting puzzle. As you are fond of saying, YMMV.

-ERD50
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Old 10-03-2014, 10:27 AM   #44
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...
"Most people?" I'd guess the person who buys the Honda Insight couldn't care less that he/she would spend incrementally more to drive 75 mph than someone with a Mercury Mountaineer. ...
For a fuller explanation - I would say that the Honda Insight owner certainly could (should?) care what it cost them to drive 75 mph versus 55 mph.

I agree with you that they may not care what the Mercury Mountaineer driver's costs are. But why would they?

But even if they spend less on fuel overall, they probably are still concerned about saving what they reasonably can. I know I am - fuel cost isn't a big issue for me, yet I try to conserve. A $1 saved is a $1 saved. At the end of the year, it really makes no difference if that $1 saved was on a $50 purchase or a $100 purchase. Your balance sheet is $1 further in the black.

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Old 10-03-2014, 11:14 AM   #45
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When considering the cost vs time saved with regard to speed, should we also consider wear and tear? Does going 75 vs 55 wear your tires faster or put more strain on the engine thus reducing it's lifespan? If so, that would need to be factored in when deciding if it's worth it to go faster or slower.
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Old 10-03-2014, 11:35 AM   #46
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When I drive the RV, I try to keep it under 60 so I get 8+ MPG. If I push it to 70, it drops into the 6's. The motorcycle gets 60 MPG and it's smiles per mile are off the chart.
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Old 10-03-2014, 11:41 AM   #47
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Anybody here trying to optimize fuel efficiency on long distance driving trips?
Not really. I bought a diesel that gets excellent mpg (low to mid 40's on the interstates) even when I'm driving 75 or 80 mph.

I usually care more about making good time when it's a matter of getting from A to B (Ohio to Florida or Ohio to California or wherever).

I got the higher mileage variant of my car (E250 rather than the E350) so that I could spend lots of time driving and not feel guilting about spending too much money on fuel.

I love to drive.
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Old 10-03-2014, 11:44 AM   #48
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When considering the cost vs time saved with regard to speed, should we also consider wear and tear?
I think it should be considered but I'm not sure what the effect (if any) there is on vehicle health and tire longevity at the speeds we are considering.

The other issue I think about is fatality rate given vehicle speed. Kinetic energy is proportional to v^2 so a crash at 75mph has 33% more energy to dissipate than 65 mph. Of course there is Walt's point driving at a speed significantly different than the flow can increase your accident likelihood.
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Old 10-03-2014, 11:53 AM   #49
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Anybody here trying to optimize fuel efficiency on long distance driving trips?
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Not really. I bought a diesel that gets excellent mpg (low to mid 40's on the interstates) even when I'm driving 75 or 80 mph.

I usually care more about making good time when it's a matter of getting from A to B (Ohio to Florida or Ohio to California or wherever).

I got the higher mileage variant of my car (E250 rather than the E350) so that I could spend lots of time driving and not feel guilting about spending too much money on fuel.

I love to drive.
Aside from what vehicles we choose to purchase, I doubt anyone tries to solely optimize fuel efficiency while driving. I'd guess we all consider the trade offs of driving time, MPG, speed limits (and other) to arrive at a speed that fits our own priorities. Some people probably drive as fast as they dare or are comfortable at (lowest time spent), some drive at posted speed limits or some fixed differential (ie, 5 mph over posted speed limits) and there are some hypermilers out there. To each his/her own.
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Old 10-03-2014, 03:15 PM   #50
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I readily admit that I paid a premium to drive a Prius. I'm a low-mileage driver, at about 30k right now, 34 months in. Of course, the Prius does save money on fuel, especially compared to the Silverado I traded in.

So, I haven't calculated it recently, but I could have bought a car for $5-10k less, with reduced mpg, and would likely not notice the difference that much on a daily/weekly basis.

The reasons I did buy a Prius: I assume fuel will generally be more expensive in the future, I plan to travel more during retirement, and add in the fact that DFW spends much of every summer at pollution level orange, so doing my small part to reduce localized pollution.
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Old 10-04-2014, 03:21 PM   #51
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At around 172 mph I get 14.4 mpg,
At 160 mph I get 16.1 mpg.

At 185 I only get I'm down to around 13 mpg and rarly go that fast. That's just to high a fuel burn to make much difference in the length of my trips.

This is at around 5000 feet and this is with no wind.

I generally cruise around 160 to 165, around 15 mpg.

My wife drives a hybrid and gets around 40 mpg to balance things out.
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Old 10-04-2014, 03:28 PM   #52
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At around 172 mph I get 14.4 mpg,
At 160 mph I get 16.1 mpg.

At 185 I only get I'm down to around 13 mpg and rarly go that fast. That's just to high a fuel burn to make much difference in the length of my trips.

This is at around 5000 feet and this is with no wind.

I generally cruise around 160 to 165, around 15 mpg.

My wife drives a hybrid and gets around 40 mpg to balance things out.
Although I haven't bought avgas in quite a while, I'm going to guess you are spending $5~6 per gallon.

Sent from my mobile device so please excuse grammatical errors.
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Old 10-04-2014, 04:37 PM   #53
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Although I haven't bought avgas in quite a while, I'm going to guess you are spending $5~6 per gallon.

Sent from my mobile device so please excuse grammatical errors.
It a little under $5 for 100ll at the SS pump. Ethanol free is $4.40 .
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Old 10-04-2014, 06:33 PM   #54
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Temperature doesn't seem to be the factor
That surprises me, because in my experience it's a big factor. I always get much better MPG numbers in summer compared to winter.
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Old 10-05-2014, 03:14 AM   #55
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Temperature doesn't seem to be the factor
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That surprises me, because in my experience it's a big factor. I always get much better MPG numbers in summer compared to winter.
We've always gotten lower MPG in winter, and it's more pronounced now that we have two hybrids. On tankfuls, I average as much as 56 MPG in summer, and as low as 44 MPG in winter. DW averages about 41 MPG in summer, and about 34 MPG in winter. When we have a long stretch of single digit temps in winter, it's really obvious, MPG and range!
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Cold weather and winter driving conditions can reduce your fuel economy significantly.

Fuel economy tests show that, in short-trip city driving, a conventional gasoline car's gas mileage is about 12% lower at 20F than it would be at 77F. It can drop as much as 22% for very short trips (3 to 4 miles).

The effect on hybrids is worse. Their fuel economy can drop about 31% to 34% under these conditions.
Fuel Economy in Cold Weather
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Old 10-05-2014, 08:18 AM   #56
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Honestly this is an area I don't worry about much. I buy cars that get decent mileage but are still fun. I take the train to work so my driving commute is typically about 3 miles. I save ~$500/mo by taking the train vs. driving.

LBYM in a huge way overall and just budget gas money each year.

When I do take a road trip, not worrying about how fast I drive and the associated impact on MPG is one my little LBYM rewards.
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Old 10-05-2014, 10:14 AM   #57
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On long trips I drive 5->9 miles over the speed limit, as long as someone passes me.
I don't want to be the fastest car on the road as I don't use a radar detector.
Personally I value my time more than the $25 I might save driving at 55.
After all I can always make more $$$, but I cannot make more lifetime.

I always use cruise control, once you do that you see who is not using it, they pass me, then drift back then pass me again and repeat.
Last trip of 800 miles, I checked the mileage and at generally 75 mph I got 34 mpg in an old toyota Camry that has a 4 cylinder engine. Tires were at 33lbs, used AC and windows were closed all the time.
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Old 10-05-2014, 10:25 AM   #58
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> Tires were at 33lbs

I've noticed that in our old Nissan Murano tire inflation made more of a difference to the highway mileage than the speed on the highway (within reason of course).

It pays to have tires inflated to the maximum PSI.
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Old 10-05-2014, 10:38 AM   #59
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We've always gotten lower MPG in winter, and it's more pronounced now that we have two hybrids. On tankfuls, I average as much as 56 MPG in summer, and as low as 44 MPG in winter. DW averages about 41 MPG in summer, and about 34 MPG in winter. When we have a long stretch of single digit temps in winter, it's really obvious, MPG and range!
Fuel Economy in Cold Weather

Poor expression on my part. My fuel economy is worse in the cold. I was speaking to driving at altitude, and was trying to say that I was comparing similar temperatures at high altitude and low as well as comparable average speeds at high and low altitudes. I am puzzled by the measured superior fuel economy my car gets at high altitude. Air resistance? If I could keep my foot out of it perhaps it would return better numbers at low altitude as well, through a reduction in air resistance. Maybe the engine computer is doing just fine compensating for the higher oxygen density at different altitudes and temperatures and it is all air resistance.

I still dislike ethanol, which is often added in winter, but that is a digression.
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Old 10-05-2014, 10:41 AM   #60
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That surprises me, because in my experience it's a big factor. I always get much better MPG numbers in summer compared to winter.
It could be the geographical differences in winter. Cars do often work a bit better in 'slightly' lower temps. At the track we had to adjust our 1/4 mile handicap times after the sun went down because the car would run about .1 seconds faster in the cooler air. (65 degrees vs 75 degrees) So perhaps if someone lives in the south and has a 'faux winter', maybe it doesn't get cold enough to hurt much.

I live in Ohio. It gets cold enough here in winter that it hurts my gas mileage noticeably.
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