Driving slower saves gas?

[Nevada]

Originally posted by: Genx87
Of course driving slower saves gas. But there is always a sweet spot. For me it appears to be ~65 mph where I can get around reasonably fast and still get 28-30 mpg in my 2001 A4.
70 and my mileage drops to 24-25.

i have a 2003 a4 and i've noticed the sweet spot for me is also around 65mph.

 

[IHateMyJob2004]

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

Pontiac G5 GT

I've done a handful of long range tests with my ext cab Chevy 1500 (4.8L V8)
55-60 mph: 21 mpg
65 mph: about 20 mpg
70 mph: still about 20 mpg
72 mph: 0.2 mpg less than 70 mph
75 mph: about 19 mpg

So, yes. People don't believe me. It's a pointless debate. The bottom line is that driving faster exponentially increases wind resistance. Don't believe me, then ask why it is easy to stand in 40 mph wind but 80 mph wind will probably knock you over. It's not twice as hard to stand now is it? Liek I said though, people are stubborn and comfortable in their ignorance.

So, why don't you people that think this is not true actually test out your own cars at 55, 65 and 75 like I have. I say what I say about driving slower improving fuel economy to be true because I've tested it out myself. I don't think, I KNOW!

 

[Oceandevi]

I got these magnets for my fuel line and my ford focus gets 50 mpg now.!!!1

 

[IHateMyJob2004]

Originally posted by: Gothgar
fuck that shit, time is money.

I used to say that at $2/gallon over my 50 miles of daily driving at 16-17 mpg (cty/hwy combined) on average.

I take it easier now and I usually get 18-19 mpg combined. Accelerate slower and drive slower on the highway (about 72 mph cruise)

 

[spidey07]

Originally posted by: IHateMyJob2004

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

Pontiac G5 GT

I've done a handful of long range tests with my ext cab Chevy 1500 (4.8L V8)
55-60 mph: 21 mpg
65 mph: about 20 mpg
70 mph: still about 20 mpg
72 mph: 0.2 mpg less than 70 mph
75 mph: about 19 mpg

So, yes. People don't believe me. It's a pointless debate. The bottom line is that driving faster exponentially increases wind resistance. Don't believe me, then ask why it is easy to stand in 40 mph wind but 80 mph wind will probably knock you over. It's not twice as hard to stand now is it? Liek I said though, people are stubborn and comfortable in their ignorance.

So, why don't you people that think this is not true actually test out your own cars at 55, 65 and 75 like I have. I say what I say about driving slower improving fuel economy to be true because I've tested it out myself. I don't think, I KNOW!

But that's your car. It isn't totally true for all cars. Some cars the sweet spot can be 75, 80, 85 Mph. Just depends on the car and gearing.

 

[Injury]

Originally posted by: tasmanian

Originally posted by: Summit
yes, because the higher the speed even if you are in the highest gear is causing you to have a higher rpm which means you are burning more gas.

I dont think its that. I think its that there is alot more wind so your car has to work harder. At 5th gear going 60-70ish my rpm is around 3000. While 50 they are alot higher.

lol... wind can affect your MPG but wind is not the cause behind the discussion here.

Ideally, you want to keep your car in the area right before it changes gears because it is runs more efficient when it's turning gears with less effort.

 

[IHateMyJob2004]

Originally posted by: broon
My durango gets better gas mileage going 80 than it does going 55-75.

Please show us your results at 55,65,75,80.

And I can guarantee you that what you said is not true.

 

[Oceandevi]

"gearing sweet spot" vs wind resistance... what matters most

"wind resistance" being the atmosphere itself, you have to drive through it.

 

[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.

 

[Injury]

Originally posted by: Drako

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

Yep, you'll be suprised how many rude looks and fingers you get .

I keep my speed at the limit in the right hand lane and don't give a crap what other people think. You can move your ass over if you wanna break the speed limit.

It's probably more annoying to other people that I use "tap and glide" on the gas pedal, with a variance of about 5MPH every few seconds, I'll let myself drop 10 below the speed limit on the expressway if I'm going uphill so I don't have to keep it floored to go and keep running efficiently.

 

[skyking]

I've done a handful of long range tests with my ext cab Chevy 1500 (4.8L V8)
55-60 mph: 21 mpg
65 mph: about 20 mpg
70 mph: still about 20 mpg
72 mph: 0.2 mpg less than 70 mph
75 mph: about 19 mpg

So, yes. People don't believe me. It's a pointless debate. The bottom line is that driving faster exponentially increases wind resistance. Don't believe me, then ask why it is easy to stand in 40 mph wind but 80 mph wind will probably knock you over. It's not twice as hard to stand now is it? Liek I said though, people are stubborn and comfortable in their ignorance.

So, why don't you people that think this is not true actually test out your own cars at 55, 65 and 75 like I have. I say what I say about driving slower improving fuel economy to be true because I've tested it out myself. I don't think, I KNOW!

^what he said.
True enough some autos have much better coefficiency of friction values, and are not as heavily penalized by speed.
Your pickup and my wife's pilot, however, are hammered by it: they push a crapload of air.
I got the EPA estimate of 23 MPG by doing 60 with the cruise.
Wind it up to 75, and it drops to 19~20.

 

[IGBT]

..wind resistance becomes a huge factor > 50mph.

 

[IHateMyJob2004]

Originally posted by: Oceandevi
"gearing sweet spot" vs wind resistance... what matters most

"wind resistance" being the atmosphere itself, you have to drive through it.

Having read the thread in its entirety I ahve to agree that this is true to some extent. But if this were true, wouldn't manufacturers make the sweet spot somewhere around 70 mph and not 90 mph?

It seems like in my truck, they really nailed it on the head. 70 mph is just about perfect for speed/fuel economy benefit. As much as it would save gas (about 5% on costs) I will not drive 55 in a 65.

I'll add, having been in England recently, those cars get insane fuel economy and going 55 is not the end of the world. What money are you making by getting somewhere sooner? The simple fact is that the answer is $0. No one here is some high flying corporate executive that needs to be to 20 meetings in one day. Fact of the matter is that saving time costs money for most here.

 

[OutHouse]

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.

 

[OutHouse]

Originally posted by: IHateMyJob2004

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

Pontiac G5 GT

I've done a handful of long range tests with my ext cab Chevy 1500 (4.8L V8)
55-60 mph: 21 mpg
65 mph: about 20 mpg
70 mph: still about 20 mpg
72 mph: 0.2 mpg less than 70 mph
75 mph: about 19 mpg

So, yes. People don't believe me. It's a pointless debate. The bottom line is that driving faster exponentially increases wind resistance. Don't believe me, then ask why it is easy to stand in 40 mph wind but 80 mph wind will probably knock you over. It's not twice as hard to stand now is it? Liek I said though, people are stubborn and comfortable in their ignorance.

So, why don't you people that think this is not true actually test out your own cars at 55, 65 and 75 like I have. I say what I say about driving slower improving fuel economy to be true because I've tested it out myself. I don't think, I KNOW!

thats great mileage on your truck. i had a 1995 GMC V8 and i was lucky to get 15mpg. one time driving through NM i had a 50+mph headwind and i bearly got 120 miles out of my FULL tank. i was getting really worried about running out of gas before i hit Raton NM to fill up again.

 

[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.

 

[Kelemvor]

I stopped speeding on the freeway and went from being lucky to get 300 miles between fill ups to now getting 350 (which is right around 30 mpg)

My cars is in it's top gear at 40. 45-50 is the sweet spot. Anything over that, wind resistance increases exponentially which means gas mileage decreases quickly as well.

Try it for your next tank of gas and you'll see the difference.

 

[Kelemvor]

Originally posted by: IGBT
..wind resistance becomes a huge factor > 50mph.

And that's the whole underlying reason why slowing down and not speeding saves so much gas.

 

[imported_Imp]

Not decelerating/accelerating your car as much by maintaining a consistent speed, slowing down to 'avoid' red lights (slow down to wait for them to go green when you get there) helps save gas.

 

[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.

 

[darkswordsman17]

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.

The drivetrain matters much more for fuel efficiency than aerodynamics, especially at speeds 80mph and below. It will start to impact things some between 50-80mph, but nowhere near as much as the drivetrain. Not only that, but the way you drive is probably more influential than aerodynamics as well. Learning how to drive more efficiently goes a long way to improving gas mileage. For instance, its not too uncommon to get stopped by a fairly long coal train in some of the communities around here, in which case instead of idling your car, turn it off, also the same with road construction (2 lane roads where they close off a lane and you have to wait for the pilot car).

If aerodynamics was such a big deal, then they would be slapping plastic underbody trays on every car these days. The thing is, the benefit from that on most cars would be negated by the added weight, so it's not worth it.

I'm not saying it doesn't matter at all, but there are several things that will have as much and probably more of an impact on fuel efficiency (namely drivetrain, weight, and tire pressure). Keep up proper maintenance, check tire pressure routinely (once a week would be a big improvement for most people), get rid of any unnecessary junk in your car, and learn to drive more efficiently will help a lot (doing all of that should easily net a 25% increase in fuel efficiency).

Another area that a lot of people don't seem to notice is aftermarket wheels/tires. Going with a larger rim increases rotational mass, and probably makes it so you have to use larger tires, which will raise rolling resistance.

 

[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.

 

[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.

 

[jonks]

quick, someone tell the OP the truth about cucumbers and pickles!

 

[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.