Price of gas getting you down? Drive SLOWER!!! (NSFW)

[Alaskan Rover]

Is that REALLY such a difficult concept?

Okay....this past week I did a small, not necessarily quantitative test. I had to rent a car. Usually I rent very economical cars that get really decent fuel mileage (30 - 40 mpg highway), but they were sold out of those. My choices were a minivan, a big Ford Crown Victoria (I must admit, those ARE extremely fun for impersonating a police car with down in the high-crime areas!!...but this time I had actual business to attend to so such friviality was out), and a fairly large new Jeep Liberty.

I chose the Liberty...nice car, leather seats, all the wingdings....but man was that thing thirsty as hell. What the hell happened to the Liberty? They increased the height and volume by about 30 percent, made it about 35 % heavier and gave it this incredibly UNaerodynamic front end.

Average highway speed was 75 - 80mph on the interstate....I had the thing following traffic at 79 mph. About 60 miles of this and I notice the freaken fuel gauge is reading 3/4 tank. Sucker had a big tank, too. The thing went through 1/4 tank just trying to drive its MASS at those speeds. I check the onboard computer...it's telling me 16.5 mpg was what I was getting at those speeds.

I devise a test.

I drive at 50mph (with flashers on) for 10 miles. MPG goes up to 24.5 mpg.....hmmm...not as much as I'd thought.

I drive at 60 mpg for 10 miles. MPG goes to approx 26 mpg.

Hmmm.

I drop it to 55 mph, and magically the fuel mileage goes up to 28.5 mpg....same conditions....level road...no wind.

I up it to 70 mph.... fuel mileage drops to 20.5 mpg avg.
you
Try 55 mph again...fuel rises back to its operational peak of 28.5 mpg.

Turns out for this vehicle, 55 mph is its efficiency sweetspot. It's that median point where engine running efficiency (amount of fuel engine is using statically at whatever rpm per unit time overall) is not yet burdened by air resistance.

Every car uses fuel in a static mode per unit time...run the vehicle in park at 2000 rpm and you'll use a surprising amount of fuel. The mpg will of course increase with increased vehicle speed in what seems a nearly linear format. But of course it's NOT linear...as efficiency is being countered by ever increasing air resistence.

Running a car at 30mph is not necessarily going to give you the best MPG, as the engine is still pumping fuel at whatever rate but your miles/time is still low.

The key, then, is to find your air-resistence/engine RPM sweetspot.

55 mph was the magic number for the gas-guzzling Liberty....but guess what?

Back in 1974 or whenever they mandated the 55mph national speed limit....they DIDN't just pull that number out of a hat....they did shitloads of testing on shitloads of vehicles....and due to the size/horsepower/aerodynamics of the average vehicle...came up with 55 mph as being a good overall efficiency sweetspot for most passenger vehicles on the road.

Maybe just happenstance that the Liberty's sweetspot was also 55...maybe not....but it made a whopping improvement in fuel economy just by driving 55!!!

55 doesn't just save lives....it saves fuel and saves YOU money!!

Try the test yourself....it works!

Okay...this post was admittedly tilting the "boring-O-meter" scale towards "Fucking Boring"....so here are some fine breasts to compensate:

Keep your cars CLEAN, bozos!!! It'll give slightly more MPG.

[The Suit]

Okay...this post was admittedly tilting the "boring-O-meter" scale towards "Fucking Boring"....so here are some fine breasts to compensate:

I'd say it tilted more towards "completely unreadable."

[TomCrac]

Are you sure that the Liberty's system isn't preprogrammed for those numbers? Are you sure that they are actual readings.

[WWCD]

I drive at 50mph (with flashers on)

I drive at 60 mpg

I drop it to 55 mph

55 doesn't just save lives....

If you were driving these speeds when the flow of traffic was 75-80, you were doing the exact opposite of saving lives.

[Alaskan Rover]

Are you sure that the Liberty's system isn't preprogrammed for those numbers? Are you sure that they are actual readings.

No...I don't believe the the Liberty's computer was preprogrammed. It's just that the vehicle's re-design resulted in a massive, wholly inefficient, very un-aerodynamic body that takes a lot more fuel to push it through the much higher air resistance encountered at 80 mph.

Every vehicle has an fuel efficiency speed sweet spot....the Liberty's just happened to be 55.

A VERY aerodynamic and lightweight coupe might indeed have a sweetspot closer to 60 or 65 mpg.

I don't know of ANY production vehicle that has an efficiency sweetspot near 80 mph.

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[Alaskan Rover]

If you were driving these speeds when the flow of traffic was 75-80, you were doing the exact opposite of saving lives.

You are correct....when only one or two vehicles are driving at 55 and everyone else is doing 80 mph, that creates an unsafe situation.

Which is EXACTLY why the national speed limit on the interstates should be dropped back down to 55 mph.

It will then save fuel AND lives.

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[Tippster]

OR we could drive cars that don't have the aerodynamics of a brick.

My Mercedes E350 4matic wagon gets better gas mileage at 75/80 than at 55.

[crashtestdummy]

Mileage is a lot like penis size, you aren't going to get an honest answer from very many. Most people figure their mileage out once, and then assume that what they get always. Ask someone who drives a 4wd diesel pickup what they get and they will claim 20 mpg whether they are pulling their D9 Dozer or driving empty.

My truck, 4wd Frontier gets 18 to 19 on the highway at 75 mph. If I go faster, the tank gets empty a lot quicker. Also if I drive 2 lane highways at 60 to 65 I can get up 24 mpg. If I have the bar round Yakima bars on my shell, my mileage drops 1 to 3 mpg. I record all of my miles and all of the gas I put into the vehicle, so these are real numbers. Physics is also real, the faster you go, the more energy it will take, and it's not linear either.

[MontuckyFried]

You are correct....when only one or two vehicles are driving at 55 and everyone else is doing 80 mph, that creates an unsafe situation.

Which is EXACTLY why the national speed limit on the interstates should be dropped back down to 55 mph.

It will then save fuel AND lives.


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It's clear that you don't live in a place like here (or just have a crapload of time on your hands). It's bad enough that the Feds forced speed limits (again) on the good people of Montana, without them dropping it to 55 (again). I'm all about maximizing your mpg when you can, but I don't exactly feel like turning my weekly 2 hour commute into a 3-4 hour one. I'm willing to spend the extra $10 once a week for that freedom. The Feds better not impose 55mph speed limits again! Freaking east-coast bureaucrats don't have en effing clue what it's like to live and work out here. God, I wish they did away with speed limits again here. Just got a ticket on Saturday coming out Bozeman for doing 91 in a 75. At least it was only $40, so I'm not complaining too much. Second one within a month, though.

[Alaskan Rover]

OR we could drive cars that don't have the aerodynamics of a brick.

My Mercedes E350 4matic wagon gets better gas mileage at 75/80 than at 55.

EXACTLY...the more aerodynaically efficient cars WILL have a higher fuel efficiency sweetspot....especially if they're also lighter as well.

But I can't help but notice that as our coupes and sedans are getting more aerodynamic, their horsepowers are going up up up...which partially obviates their efficiency if your opting for a 380 hp 8 cylinder in the same vehicle that has a base engine of a 180hp V6 (180hp is PLENTY!!)...I'm not talking about your Mercedes, just a generic, non-specific example car.

And while we are seeing these more aerodynamic bodies on passenger cars, how come light trucks are getting HUGE on the outside for the same seating capacity/pick-up bed capacity/towing capacity as a few years ago....That's a LOT of excess wind barrier to be pushing through at 80 mph!!! See the 2012 Ford F-150 vs the 2007 Ford F-150 to see what I'm talking about....the frickin' things are nearly the same size as a F-600 now!!!

WTF...are they trying to turn the damn F-150s into Personal Peterbilts???



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[BmillsSkier]

Who are you to tell me that 180hp is plenty?

[hawkgt]

HEY!!! You want to tell Alyssa to get off the dam lambo?!? friggin' clit ring tore the shit out of the bently paint last year...

[The AD]

EXACTLY...the more aerodynaically efficient cars WILL have a higher fuel efficiency sweetspot....especially if they're also lighter as well

Sorry, this is false. Drag increases with speed. The faster you go, the more drag. Aerodynamics are going to reduce this drag, but it will still go up as a function of velocity. More drag means more power needed by the engine. How the engine is geared is going to affect that sweet spot, but vehicle aerodynamics is not.

[MontuckyFried]

But I can't help but notice that as our coupes and sedans are getting more aerodynamic, their horsepowers are going up up up...which partially obviates their efficiency if your opting for a 380 hp 8 cylinder in the same vehicle that has a base engine of a 180hp V6 (180hp is PLENTY!!)...I'm not talking about your Mercedes, just a generic, non-specific example car.

There's actually something to be said for having high horsepower for efficiency. One of my cars has a 405 horse V-8. Thus, it takes it very little effort to cruise down the highway, especially with it's great 6th gear. With that kind of power, it doesn't make too much of a difference whether I'm going 60 or 80, uphill or downhill. For what it's worth, I average about 26 on the highway. Do I get the mpg that I used to in my '04 Mazda 3 hatch? Nope, but then again, that car only got around 30 on the highway. I'm willing to deal with the "whopping" 3-4 mpg difference to enjoy having triple the power.

As far as the trucks go, you're right in that they're getting obnoxiously huge, BUT their new ultra powerful V-8's and Twin-Turbo V-6's (ref: F150's EcoBoost) are getting better MPG than many compact trucks of yore, while having way more capability. It would be really nice if we could get a diesel F-150 or Tacoma, though.

[MontuckyFried]

Alaskan Rover's car?



With it's 300cc, 13 horsepower engine, the BMW Isetta may have been the pinnacle of efficiency, getting between 50-70 mpg. I'm sure the world would be a better place if we all drove these (according to AR). I kid. I kid.

[uglymoney]

Agree with The AD. You can't get away from e=mv2. It basically takes four times as much energy to push your car through the air at 60 than 30 mph and four times more energy to push it at 120 instead of 60. This is why a 100 hp car go a hundred miles an hour but the same car with 200 hp can't do 200. 400 hp and we might be talking.

It could be that the tranny on the Jeep doesn't lock up in high gear at 50 mph or it was locking and unlocking as the op was throttling it. This would explain the slightly better one time mileage readings at 55.

Mileage is a lot like penis size, you aren't going to get an honest answer from very many. Most people figure their mileage out once, and then assume that what they get always. Ask someone who drives a 4wd diesel pickup what they get and they will claim 20 mpg whether they are pulling their D9 Dozer or driving empty.

My truck, 4wd Frontier gets 18 to 19 on the highway at 75 mph. If I go faster, the tank gets empty a lot quicker. Also if I drive 2 lane highways at 60 to 65 I can get up 24 mpg. If I have the bar round Yakima bars on my shell, my mileage drops 1 to 3 mpg. I record all of my miles and all of the gas I put into the vehicle, so these are real numbers. Physics is also real, the faster you go, the more energy it will take, and it's not linear either.

Yes. I'm one who takes the mileage every time. It varies based on so many factors. If you don't do it you don't know. And the trip computer on my wifes Runner always runs a few percentage points higher than what we're really getting.

And Tippster I don't think so man. Not unless you're holding condoms out the window when you drive slow.

[uglymoney]

There's actually something to be said for having high horsepower for efficiency. One of my cars has a 405 horse V-8. Thus, it takes it very little effort to cruise down the highway, especially with it's great 6th gear.

They do a bunch of trick things to get 26 mpg out of your huge engine but the size of the engine is not one of the tricks. Super tall 6th gear for one. The fact that the big old motor can hold that gear makes it pleasing to drive but a smaller motor with all the same tricks would get better mileage - though you or the computer might have to shift more often.

[Alaskan Rover]

Alaskan Rover's car?



With it's 300cc, 13 horsepower engine, the BMW Isetta may have been the pinnacle of efficiency, getting between 50-70 mpg. I'm sure the world would be a better place if we all drove these (according to AR). I kid. I kid.

I love those Isettas!!! Pretty much a motorcycle morphed into a three-wheeled car. 13hp does seem a little low, though. My rover of the same approxiate vintage is approximately 72hp...although that's BHP....net would probably be sixty something...66 rings a bell. Unfortunately the engine is coupled to a tranny with gearing as high as 55:1 and the rover is running 3000 rpm at 50 mph..so it's no shining star on the highway in speed NOR fuel efficiency...but it DOES get up to 23 mpg when tuned well...which ain't too bad for such high-ratioed gearing.

Those new Smartcars get SHAMEFULLY low mpg on the highway for what they are....mid-40s. Seems they SHOULD be at least in the fifties. A friend of mine has a 2000 VW Jetta Diesel that REGULARLY gets 55 mpg on the highway!

Here's exactly what we should be driving:








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[carvedog]

Okay...this post was admittedly tilting the "boring-O-meter" scale towards "Fucking Boring"....so here are some fine breasts to compensate:

Gooooooood Lord. So I drop in to an Ak Rover thread that promises NSFW.

Since when is side boob and ass crack NSFW? I show more than that to the neighbor in the morning doing yoga. WTF dude?

I call it bullshit false advertising. Either that or I am completely blinded by the friviality that I had to wade through up there. Where you trying to say trivial ity? or what. Fuck I'm out.

[Alaskan Rover]

Gooooooood Lord. So I drop in to an Ak Rover thread that promises NSFW.

Since when is side boob and ass crack NSFW? I show more than that to the neighbor in the morning doing yoga. WTF dude?

I call it bullshit false advertising. Either that or I am completely blinded by the friviality that I had to wade through up there. Where you trying to say trivial ity? or what. Fuck I'm out.

Well, the thread was originally destined for PolyAsswipeHat...but I thought that even 1.5 square inches of side tit might be enough to give DBT a coronary...so strictly for DBT's heart-health, I decided to move the thread over here to the Padded Room.

My mistake was not upgrading the pictorial aspects to better suit the Padded Room versus the originally intended Polyasshat.

I can rectify that herewith for you:







My God....my eyeballs are MAIMED for life...thanks a LOT, Carvedog...now I'm blind!!

But I WILL try to fix the bad link to the third pic in the O.P.....that's the only one that contained fairly decent aspect.

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EDIT: There...third pic in O.P. is fixed.....I think. Of course, anyone is free to add their own NSFW pics of course...but try to keep them somewhat applicable to cars (or fuel??....nahh...scratch that...too many psychos out there).

[DJSapp]

You are correct....when only one or two vehicles are driving at 55 and everyone else is doing 80 mph, that creates an unsafe situation.

Which is EXACTLY why the national speed limit on the interstates should be dropped back down to 55 mph.

It will then save fuel AND lives.

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Actually, this is a chicken and the egg problem. From the EPA test criteria: "The highway test has a top speed of 60 miles per hour, and an average speed of only 48 miles per hour." (more boring shit here: http://www.epa.gov/fueleconomy/420f06069.htm).

Car manufacturers need to raise fuel economy standards to meet gov't requirements, therefore cars are designed to run efficiently there. If the fuel economy tests were changed to a max speed of 70, and average speed of 65, manufacturers would change the gear ratios to improve fuel economy. This is why sports cars and imports do better at higher speed, since they aren't designed to pass this stupid test.

[jfost]

Actually, this is a chicken and the egg problem. From the EPA test criteria: "The highway test has a top speed of 60 miles per hour, and an average speed of only 48 miles per hour." (more boring shit here: http://www.epa.gov/fueleconomy/420f06069.htm).

Car manufacturers need to raise fuel economy standards to meet gov't requirements, therefore cars are designed to run efficiently there. If the fuel economy tests were changed to a max speed of 70, and average speed of 65, manufacturers would change the gear ratios to improve fuel economy. This is why sports cars and imports do better at higher speed, since they aren't designed to pass this stupid test.

good thing we are getting rid of the EPA!!!

[GeezerSteve]

What The AD and uglymonkey said. Drag increases exponentially with air speed.

[Downbound Train]

You are correct....when only one or two vehicles are driving at 55 and everyone else is doing 80 mph, that creates an unsafe situation.

Which is EXACTLY why the national speed limit on the interstates should be dropped back down to 55 mph.

It will then save fuel AND lives.

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Time is money AK. 20 miles per hour less = 20 minutes per hour wasted. What's your time worth? How much would that lower the productivity of America. We're supposed to do things to HELP the economy AK. Not wreck it even more for some psycho religion called enviromentalism.

[Alaskan Rover]

What The AD and uglymonkey said. Drag increases exponentially with air speed.

I don't think anyone here inferred that it is a linear function. In fact, in my original post, I stated:

" But of course it's NOT linear...as efficiency is being countered by ever increasing air resistence."

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