Driving slower saves gas?

[darkswordsman17]

Originally posted by: IHateMyJob2004
technophile82,

Wind resistance affects(sp?) the amount of energy required to push your car through the air. The faster you go, the more energy that is required. And since wind resistance increases exponentially with vehicle velocity, the faster you go, the amount of energy required increases exponentially. There fore you burn more gas when going faster.

Also, it has nothing to do with being a car guy and everything to do with physics.

Yes, but that is reasoning that the vehicle is using the same gear for every speed. Mechanical efficiency allowed by modern transmissions changes optimum efficiency speed, and it varies from car to car. Even when comparing say a small SUV to a midsize sedan, where both use the same drivetrain, the main thing that makes the car more efficient is that it often weighs a good 500lbs or more less than the SUV. It takes more fuel to accelerate more mass to the same speed. Acceleration is the key area where larger vehicles added fuel consumption comes from, not maintaining speed. Yes it is a function of both mass and wind resistance, but the mass is a bigger part of it for typical driving speeds.

 

[Dacalo]

Originally posted by: fatpat268

Originally posted by: Citrix
i have a friend who is a truck driver, his company truck has a governor (sp?) on it and they company he drives for just tweaked it down so none of their trucks can go past 68.

My dad's (who is also a trucker) company truck was recently set down from 63 mph to 60 mph.

Apparently it makes a difference.

Even more so trucks which tend to be very heavy and much less aerodynamic.

 

[gnumantsc]

I tend to accelerate really slowly making sure I don't go past 2000rpms from a dead stop. I see all these other cars zoom by or try to make me go faster when the light is red. I don't give a crap that the light is red and you want me to waste my gas?

When going on a long trip I would rather drive faster than to save gas if its an hour difference that's a big difference in time but for say going to work an extra 5 minutes is no big deal.

 

[Eli]

This is a joke, right?

Of course driving faster uses more gas. There are huge numbers of variables, but it takes energy to push you through our atmosphere. The faster you're going, the more it requires.

 

[Oyeve]

Originally posted by: Eli
This is a joke, right?

Of course driving faster uses more gas. There are huge numbers of variables, but it takes energy to push you through our atmosphere. The faster you're going, the more it requires.

Yep, it's all simple physics. Sometimes you have no choice but to drive fast though. If everyone is doing 80 on the highway and you arent, it could be dangerous, especially in L.A., last time I was there EVERYONE was doing 90-100mph. I was freaking out just trying to keep up! And I was driving a Jeep that the tires were recalled back in 2000-2001 and I havent received my replacement tires yet. Man, I never want to go thru that again.

 

[Eli]

Originally posted by: skyking

Originally posted by: technophile82
a lot of people are saying wind resistance, but doesnt it come down to rpms in the end? i mean if wind resistance makes your engine 'work harder' doesnt that mean its revving faster, and thus eating more gas? or is there something else...like the engine uses more gas per revolution at different rpms? i'm not a car guy so i dont really know.

No, RPMs are less important than you think. Load is the wind resistance and friction.
at any give RPM, your engine can use more or less fuel to maintain that RPM due to the load.
I drive trucks, cars, boats and fly planes. The trucks, boats and planes have very good charts on LB/BHP/HR at different RPMs.
The efficiency varies a little with RPM, but the HP needed is the bigger factor.

Exactly what I was going to post.

RPM isnt the only thing that matters. You have to think of the throttle position too.

 

[Eli]

Originally posted by: lozina

Originally posted by: IHateMyJob2004

Originally posted by: lozina

Originally posted by: Billb2
Set the cruse on 55, and be surprised.

cruise sucks ass

it causes you to brake on downhills and rev the RPMS up on uphills

Your cruise control does braking? Actually applying the brakes. That is Amazing. What kind of car is it?

As for uphills, wouldn't you need to apply gas to go up it anyways? Your point is moot.

No, it does not apply brakes but it downshifts to lower your speed down to the speed you set. This is wasteful.

See the proper way to negotiate hills is to coast downhill and when you see you are approaching an uphill throttle up prior to reaching the uphill to gain speed then maintain constant rpms as you climb up even if it means you slow down considerably if the hill is sufficiently large.

this is the most natural way to drive and the most efficient in terms of mpgs.

This is incorrect, partially.

The transmission downshifting to maintain speed down a hill saves gas. The engine is not burning any when the wheels are driving the engine.

However, if you coast down the hill, you are using gas idling.

And if you are slowing down, you aren't maintaining constant RPMs.

 

[Mermaidman]

Another benefit of driving slower is improved mental health because I no longer run into slow traffic . . . I AM the slow traffic :laugh:

My car's sweet spot ~ 65-70 MPH.

 

[torpid]

It seems that I purchased the wrong year A4. I had an '02 A4 and my sweet spot was 0mph. Any faster and the car broke down. I ended up trading it in, fortunately.

 

[Svnla]

I drive a bit slower than the posted speed and in the right hand side.

70 MPH, I will drive 60 to 65
60 MPH, 55 or so

It helps a bit, about 5% more...ie, I used to get 300 miles per 13 gallons, now I get about 320 or so. Not much but it does help over the whole year.

 

[Eli]

Driving my Insight has taught me a lot about fuel economy.

I get the best fuel economy in town using the 1-2-5 shift method. And I floor it.

1st - floored to ~3,000RPM, shift, floor 2nd to desired speed, shift into 5th.

Originally posted by: gnumantsc
I tend to accelerate really slowly making sure I don't go past 2000rpms from a dead stop. I see all these other cars zoom by or try to make me go faster when the light is red. I don't give a crap that the light is red and you want me to waste my gas?

When going on a long trip I would rather drive faster than to save gas if its an hour difference that's a big difference in time but for say going to work an extra 5 minutes is no big deal.

I've found that accelerating slowly does me no favors. It's a time vs. instant mpg thing. I wonder if I could gather enough data to actually run the numbers.

When accelerating, the Insight engine uses a lot more fuel than it normally does. If it takes me say, a minute to get to my desired speed, I might only be getting 35MPG during that time.

However, if I employ the 1-2-5 shift, I will only be getting 20MPG while accelerating hard, but thats only the first 20 seconds or so of the minute. Now that I'm up to speed, I can shift into 5th, lean burn will kick in and I will get 65+MPG for the remainder of the minute.

 

[HardcoreRobot]

absolutely

thats why many cities let hybrids buses and motorcycles use the HOV lanes and force the people with crappy cars to sit in stop and go traffic

 

[Svnla]

Originally posted by: Auggie
It's not a gas-rate issue, Summit - it's the fact that wind resistance geometrically increases as speed linearly increases.

The efficiency of an engine is nearly the same at 40mph or 80mph. The force of the wind resistance is incredibly different.

QFT, Consumer Reports did a report on this subject recently. IIRC, it said "exponentialy" increase from 60 to 70, and from 70 to 80 and so on.

http://www.consumerreports.org...20for%20fuel%20dollars

 

[gnumantsc]

Well I drive automatic so I tend not to speed up quickly. I drive a 3.4L Pontiac GrandAM and pressing a bit harder feels I'm not doing much but feeling the gas being sucked up and goign nowhere. I usually speed up slowly and not quickly although I tend to let my foot go on the gas earlier when I see the light red and usually by the time I get there it just turned green so I pass the people who rushed to the light.

 

[brownzilla786]

Originally posted by: PhaZe
you have practice hypermiling

http://www.cnn.com/video/#/vid...obrien.hypermiling.cnn

http://www.hypermiling.com/

thats a bit psychotic

If you turn off the car don't you lose power steering and brakes?

 

[spidey07]

Originally posted by: brownzilla786

Originally posted by: PhaZe
you have practice hypermiling

http://www.cnn.com/video/#/vid...obrien.hypermiling.cnn

http://www.hypermiling.com/

thats a bit psychotic

If you turn off the car don't you lose power steering and brakes?

Yes. Don't do this.

 

[Eli]

Originally posted by: brownzilla786

Originally posted by: PhaZe
you have practice hypermiling

http://www.cnn.com/video/#/vid...obrien.hypermiling.cnn

http://www.hypermiling.com/

thats a bit psychotic

If you turn off the car don't you lose power steering and brakes?

Yes. Never turn an automatic off while moving, unless you know what you're doing.

Not as big of a deal with a stick.

 

[BlahBlahYouToo]

Originally posted by: Scouzer
80km/h - 40-45mpg
110km/h - 34-36mpg

Pontiac G5 GT

shens.

 

[Raizinman]

Miles per gallon is not the whole picture.

If you have to travel 70 miles and are traveling 35 MPH, then you will arrive in 2 hours with an approximate 26 miles per gallon. In my car.

If you travel the same 70 miles and travel 70 mph, then you will arrive in 1 hour with an approximate 20 miles per gallon.

From that perspective, is traveling 70 mph more or less fuel efficient? Traveling 70 MPH will have your engine OFF for one full hour. This savings should be more than enough to cover the difference in the MPG, not to mention time is money.

 

[bunnyfubbles]

Originally posted by: lozina

Originally posted by: IHateMyJob2004

Originally posted by: lozina

Originally posted by: Billb2
Set the cruse on 55, and be surprised.

cruise sucks ass

it causes you to brake on downhills and rev the RPMS up on uphills

Your cruise control does braking? Actually applying the brakes. That is Amazing. What kind of car is it?

As for uphills, wouldn't you need to apply gas to go up it anyways? Your point is moot.

No, it does not apply brakes but it downshifts to lower your speed down to the speed you set. This is wasteful.

See the proper way to negotiate hills is to coast downhill and when you see you are approaching an uphill throttle up prior to reaching the uphill to gain speed then maintain constant rpms as you climb up even if it means you slow down considerably if the hill is sufficiently large.

this is the most natural way to drive and the most efficient in terms of mpgs.

Highways (where cruise is put to best use) generally do not have the rolling hills required for the driving you're talking of. Also manuals would be immune to having cruise shift your gears

 

[spidey07]

Originally posted by: Raizinman
Miles per gallon is not the whole picture.

If you have to travel 70 miles and are traveling 35 MPH, then you will arrive in 2 hours with an approximate 26 miles per gallon. In my car.

If you travel the same 70 miles and travel 70 mph, then you will arrive in 1 hour with an approximate 20 miles per gallon.

From that perspective, is traveling 70 mph more or less fuel efficient? Traveling 70 MPH will have your engine OFF for one full hour. This savings should be more than enough to cover the difference in the MPG, not to mention time is money.

wait, what?

Fuel efficiency is defined as miles per gallon, the distance you go per unit fuel. In your scenario you're using more fuel to do the same task - drive 70 miles. Therefore it's much less efficient. Doesn't have anything to do with the car being on or off.

 

[Eli]

Originally posted by: Raizinman
Miles per gallon is not the whole picture.

If you have to travel 70 miles and are traveling 35 MPH, then you will arrive in 2 hours with an approximate 26 miles per gallon. In my car.

If you travel the same 70 miles and travel 70 mph, then you will arrive in 1 hour with an approximate 20 miles per gallon.

From that perspective, is traveling 70 mph more or less fuel efficient? Traveling 70 MPH will have your engine OFF for one full hour. This savings should be more than enough to cover the difference in the MPG, not to mention time is money.

What?

It's more fuel efficient for you to travel at 35MPH, period. You aren't saving any money by getting there earlier and having your car sit off. :laugh:

At 35MPH, it takes 2.692 gallons.

At 70MPH, it takes 3.5 gallons, using your figures. Which is more fuel efficient?

This thread isn't about time.

 

[PieIsAwesome]

If I remember my physics correctly:
Yes, because the greater the velocity, the greater the wind resistance, and wind resistance is the greatest force your car needs to overcome. If there were no wind resistance/atmosphere and if you were to drive in a straight line on level ground you would merely accelerate to your desired velocity and leave it at that.

 

[91TTZ]

Originally posted by: OdiN
It's not necessarily how fast you're going. It's more the RPM's, vs. speed. The optimal speed would be where RPM's aren't high, but you're still travelling fast, as in 65MPH. As you go faster, your RPM's will be higher and you will use more gas - your engine is working harder to maintain the higher speed.

No, it's mostly about speed. It takes energy to overcome wind resistance.

 

[RbSX]

The whole theory of driving slow to save gas is a rock of shit, it's known as hypermilling.

The fact is that it really doesn't matter how fast your car is going, revving to 5k can get you to 30kph in 1st year, or revving to 2000rpm can get you to 30 in second.

At a certain point though going slower is a better idea because you have to figure out where your car is aerodynmically most effective, at a certain point going faster then WILL be less efficient no matter if you gear down or not.