Ouch my mileage sure drops at speed

[mercanucaribe]

Originally posted by: sao123

Originally posted by: Scouzer
Car: 2006 Pontiac Pursuit GT

I have an on board fuel economy gauge. It is very accurate. I have tested it on two fuel tanks in the past, and it was within .2 mpg of my calculations.

When I was driving through the city, the speed limit was between 44 and 56mph (converted from KMPH). In about 20 miles of driving with this, including three red lights (complete stops) and numerous times speeding up and slowing down, I managed 42mpg.

After this, I finally got out on to the open highway where the speed limit is 68mph. I turned on the cruise control at exactly 68mph, and watched the fuel economy. Over the next two hours my economy dropped and averaged at 31mpg.

Ouch. Sucks. And it happens every time.

Why don't they make 5th gear higher? My car turns at about 2700rpm to maintain 68mph, seems higher than necessary...

Several fuel economists suggested that they make 6th gear which would run at 65mph at 1800rpms thus making fuel economy peak at 65 instead of 55... but thent he government claimed that would encourage people to drive 65mph all the time thus creating a more sufficient speeding problem...
:thumbsdown:

The speed limit is 65-75 in most places. The government is in bed with oil companies anyway though.

 

[iamaelephant]

I don't know why people are doubting the car will make 2700rpm in 5th. I had a Falcon with a 4.11:1 diff ratio and the thing would be well over 3000rpm at 100km/h (...sigh around 60mi/h).

 

[Imdmn04]

Air resistance EXPONENTIALLY increases as speed increases.

That is why in the Bugatti Veyron, you only need 300hp to go the first 150mph, but to hit 250mph, you need 1000hp. That is an increase of 700hp for 100mph gain!

 

[Parasitic]

Our Camry turns 2700rpm @ 70 mph with a 4-speed.
31 mpg is pretty good - only in rare cases will I be able to average over 30mpg. Most of the time I hover 26-27mpg.

 

[d33pt]

if your 5th gear was higher, you'd need more power to overcome drag, so you'd actually waste more gas.

 

[Shawn]

I get less than 19mpg in the miata when I do over 100mph. 21mpg when I average around 90mph. 25mpg at 80 and about 28mpg at 70.

 

[HannibalX]

I love car threads. The pseudo truths that everyone heard from their mechanic, neighbor, etc. are hilarious.

 

[PHiuR]

I drive at 80MPH and don't give a crap about MPG...perhaps thats why I'm poor. Nope, not why.

 

[miri]

I have a 2005 Scion TC. It gets horrendous city mpg, 22-27, but when I took a 3000 mile roadtrip I got 36-37MPG cruising at 75-80MPH and near 4000rpm with a 5 speed. Dunno why my gas mileage was so good at high speeds, and my car was loaded down with all my stuff.

 

[AgaBoogaBoo]

Originally posted by: b0mbrman

Originally posted by: spidey07
That's why many cars come with 6 speeds these days.

The type of cars that I've driven w/6 gears didn't do it for the sake of fuel economy

Agreed. Even in the sports cars that have a 6 speed for performance, I feel they should make the last gear even taller... that's what I'll be using for highway cruising and really wouldn't mind 80 mph @ 2000 rpm or something in your standard Evo/STi/etc.

I would agree with the OP that the last gear should be taller, consider it a highway only gear or whatever... would work very well when you just need to maintain a certain speed.

 

[BUTCH1]

Originally posted by: MercenaryForHire

Originally posted by: BUTCH1
Is that CRPM?? (Canada's RPM)..No modern vehicle will turn 2700@68 MPH unless it's been modified for racing and no
auto will get WORSE MPG @ cruising speed than in traffic (except hybrids of course) please, drag your owners manuel
into the crapper and read it before any more posting, you lack the automotive knowledge that a 10 year old in the USA
takes for granted, making YOU look stupid..

Pursuit GT = 25.1" tire diameter, 0.69:1 gear ratio in 5th, 3.84:1 final drive.

Do the math yourself if you like.

- M4H

OK, I did the math, got the same spec's as you Here then used This to calculate tire dimensions then used This to calculate final speed@2700RPM and came to
152.2 MPH which of course is wrong. So now that I've overworked my 11 brain cells on this I'm going to stun
them with a leftover Loritab and go plant shopping, good afternoon everyone...

 

[OS]

Originally posted by: BUTCH1

Originally posted by: MercenaryForHire

Originally posted by: BUTCH1
Is that CRPM?? (Canada's RPM)..No modern vehicle will turn 2700@68 MPH unless it's been modified for racing and no
auto will get WORSE MPG @ cruising speed than in traffic (except hybrids of course) please, drag your owners manuel
into the crapper and read it before any more posting, you lack the automotive knowledge that a 10 year old in the USA
takes for granted, making YOU look stupid..

Pursuit GT = 25.1" tire diameter, 0.69:1 gear ratio in 5th, 3.84:1 final drive.

Do the math yourself if you like.

- M4H

OK, I did the math, got the same spec's as you Here then used This to calculate tire dimensions then used This to calculate final speed@2700RPM and came to
152.2 MPH which of course is wrong. So now that I've overworked my 11 brain cells on this I'm going to stun
them with a leftover Loritab and go plant shopping, good afternoon everyone...

I hope you're using half the diameter for radius, cause that would explain why you're around 200% off

 

[sao123]

Originally posted by: mercanucaribe

Originally posted by: sao123

Originally posted by: Scouzer
Car: 2006 Pontiac Pursuit GT

I have an on board fuel economy gauge. It is very accurate. I have tested it on two fuel tanks in the past, and it was within .2 mpg of my calculations.

When I was driving through the city, the speed limit was between 44 and 56mph (converted from KMPH). In about 20 miles of driving with this, including three red lights (complete stops) and numerous times speeding up and slowing down, I managed 42mpg.

After this, I finally got out on to the open highway where the speed limit is 68mph. I turned on the cruise control at exactly 68mph, and watched the fuel economy. Over the next two hours my economy dropped and averaged at 31mpg.

Ouch. Sucks. And it happens every time.

Why don't they make 5th gear higher? My car turns at about 2700rpm to maintain 68mph, seems higher than necessary...

Several fuel economists suggested that they make 6th gear which would run at 65mph at 1800rpms thus making fuel economy peak at 65 instead of 55... but thent he government claimed that would encourage people to drive 65mph all the time thus creating a more sufficient speeding problem...
:thumbsdown:

The speed limit is 65-75 in most places. The government is in bed with oil companies anyway though.

The national speed limit is still 55 on all non "limited-access" highways... (interstates only make up about 2% of all roads)

 

[Accipiter22]

Originally posted by: Scouzer
Car: 2006 Pontiac Pursuit GT

I have an on board fuel economy gauge. It is very accurate. I have tested it on two fuel tanks in the past, and it was within .2 mpg of my calculations.

When I was driving through the city, the speed limit was between 44 and 56mph (converted from KMPH). In about 20 miles of driving with this, including three red lights (complete stops) and numerous times speeding up and slowing down, I managed 42mpg.

After this, I finally got out on to the open highway where the speed limit is 68mph. I turned on the cruise control at exactly 68mph, and watched the fuel economy. Over the next two hours my economy dropped and averaged at 31mpg.

Ouch. Sucks. And it happens every time.

Why don't they make 5th gear higher? My car turns at about 2700rpm to maintain 68mph, seems higher than necessary...

2700??? My 4 cylander chevy malibu turns about 2300-2400 for that

 

[KingofCamelot]

Originally posted by: iamaelephant

Originally posted by: Scouzer
Actually, the thoughts in my mind was using archaic units to please stupid Americans.

I almost typed "stupid" but decided I'm sick of being banned Some Americans are sensitive to having their wittle feewings hurt I've found.

Yup, us stupid Americans with our archaic systems.

Hows that constitutional monarchy working out for you two? The Queen doing well today?

 

[Scouzer]

Originally posted by: KingofCamelot

Originally posted by: iamaelephant

Originally posted by: Scouzer
Actually, the thoughts in my mind was using archaic units to please stupid Americans.

I almost typed "stupid" but decided I'm sick of being banned Some Americans are sensitive to having their wittle feewings hurt I've found.

Yup, us stupid Americans with our archaic systems.

Hows that constitutional monarchy working out for you two? The Queen doing well today?

Pretty good, thanks. We don't have to pay for it, and the British government holds no power here, so I'd say it works dandy.

 

[BUTCH1]

Originally posted by: OS

Originally posted by: BUTCH1

Originally posted by: MercenaryForHire

Originally posted by: BUTCH1
Is that CRPM?? (Canada's RPM)..No modern vehicle will turn 2700@68 MPH unless it's been modified for racing and no
auto will get WORSE MPG @ cruising speed than in traffic (except hybrids of course) please, drag your owners manuel
into the crapper and read it before any more posting, you lack the automotive knowledge that a 10 year old in the USA
takes for granted, making YOU look stupid..

Pursuit GT = 25.1" tire diameter, 0.69:1 gear ratio in 5th, 3.84:1 final drive.

Do the math yourself if you like.

- M4H

OK, I did the math, got the same spec's as you Here then used This to calculate tire dimensions then used This to calculate final speed@2700RPM and came to
152.2 MPH which of course is wrong. So now that I've overworked my 11 brain cells on this I'm going to stun
them with a leftover Loritab and go plant shopping, good afternoon everyone...

I hope you're using half the diameter for radius, cause that would explain why you're around 200% off

Your right, the calculator specified the radius not the diameter. Using the radius it
comes out to 101.5 MPH, still way too high. Oh well, Guess I'll just take the OP's
word for it, looks like a nice little car BTW...

 

[iamaelephant]

Originally posted by: KingofCamelot

Originally posted by: iamaelephant

Originally posted by: Scouzer
Actually, the thoughts in my mind was using archaic units to please stupid Americans.

I almost typed "stupid" but decided I'm sick of being banned Some Americans are sensitive to having their wittle feewings hurt I've found.

Yup, us stupid Americans with our archaic systems.

Hows that constitutional monarchy working out for you two? The Queen doing well today?

As Scouzer said, the Queen holds absolutely no power over here. You don't know anything about my country :roll: Just start using the metric system you imbeciles.

 

[mugs]

Originally posted by: BUTCH1
Is that CRPM?? (Canada's RPM)..No modern vehicle will turn 2700@68 MPH unless it's been modified for racing and no
auto will get WORSE MPG @ cruising speed than in traffic (except hybrids of course) please, drag your owners manuel
into the crapper and read it before any more posting, you lack the automotive knowledge that a 10 year old in the USA
takes for granted, making YOU look stupid..

My Civic (2003) would be at ~3400 RPM at 68 mph in 5th gear. It's almost exactly 20 mph per 1000 RPM in 5th gear.

Edit: Wow, in this entire thread I don't think anyone is even discussing the OP's question. It's all about units of measure.

OP, I'm guessing part of the problem is that people pay attention to EPA fuel economy ratings, which are measured at 55 mph. So for a car that uses fuel economy as a selling point, they may sacrifice actual fuel economy for a better number on the sticker. The EPA is changing the way they measure fuel economy though.

 

[BUTCH1]

I've got the same MPG readout on my GM that OP has, if you reset it the MPG will initially read way
too high. It's not meant to measure a single 20Mi trip through town. My trip to work is local roads
to and I-95 back home, my MPG stays@26.2 for the entire trip. If I take local roads both ways it
will lower back down to 24.2 in a day or two. This is why he thinks his city MPG is better than his
Hy. MPG.

 

[DivideBYZero]

Originally posted by: Accipiter22

Originally posted by: Scouzer
Car: 2006 Pontiac Pursuit GT

I have an on board fuel economy gauge. It is very accurate. I have tested it on two fuel tanks in the past, and it was within .2 mpg of my calculations.

When I was driving through the city, the speed limit was between 44 and 56mph (converted from KMPH). In about 20 miles of driving with this, including three red lights (complete stops) and numerous times speeding up and slowing down, I managed 42mpg.

After this, I finally got out on to the open highway where the speed limit is 68mph. I turned on the cruise control at exactly 68mph, and watched the fuel economy. Over the next two hours my economy dropped and averaged at 31mpg.

Ouch. Sucks. And it happens every time.

Why don't they make 5th gear higher? My car turns at about 2700rpm to maintain 68mph, seems higher than necessary...

2700??? My 4 cylander chevy malibu turns about 2300-2400 for that

My inline 6 M3 runs at about 2800 @ 70mph. What is your point?

 

[MercenaryForHire]

Originally posted by: BUTCH1
Your right, the calculator specified the radius not the diameter. Using the radius it comes out to 101.5 MPH, still way too high. Oh well, Guess I'll just take the OP's word for it, looks like a nice little car BTW...

You're still smoking rock. I get 74.2mph from those numbers - which is perfectly plausible that the OP would see 68 given speedo error + wind resistance + margin of error.

Originally posted by: mugs
My Civic (2003) would be at ~3400 RPM at 68 mph in 5th gear. It's almost exactly 20 mph per 1000 RPM in 5th gear.

What tires are you on? 3400 in 5th would put me around 80mph.

- M4H

 

[PricklyPete]

Originally posted by: b0mbrman

Originally posted by: spidey07
That's why many cars come with 6 speeds these days.

The type of cars that I've driven w/6 gears didn't do it for the sake of fuel economy

My Toyota Tacoma sure doesn't. The Sixth gear in my manual gear box is lower than the Fifth gear in the auto gear box. My fuel economy suffers at higher speeds.

 

[Zenmervolt]

Drag increases exponentially. The power required to move through a fluid increases with the cube of speed, so to go twice as fast takes eight times the power. Given the mileage it sounds like you have a 4-cylinder. 2,700 RPM at almost 70mph is actually pretty tall gearing for a 4-cylinder, in most cases 4-cylinders are turning about 3,000 RPM at 70 mph. The reason that 5th is not taller is because your engine doesn't make enough power for that.

ZV

 

[Syrch]

man im happy when i get 21...stop complaining