how to increase better gas mileage
11-09-2004, 03:31 AM
#5
It's chrome alright...
Join Date: Dec 2001
Posts: 4,009
Never go above 3k rpm.
Never floor it.
Shift as soon as you can, and keep it in the highest gear possible.
Use a/c as little as possible, and only above 40mph.
Keep the windows rolled up as much as possible, and only roll them down below 40mph.
Keep OD *on*. Higher gears = better mileage. The ECU knows when to shift.
........basically, don't to anything that might be fun and your mileage will go up.
Oh, and DO NOT hold in the clutch and coast.... *if* you save $20 over the next 5,000 miles it'll be offset by needing to replace your clutch that much sooner.
Never floor it.
Shift as soon as you can, and keep it in the highest gear possible.
Use a/c as little as possible, and only above 40mph.
Keep the windows rolled up as much as possible, and only roll them down below 40mph.
Keep OD *on*. Higher gears = better mileage. The ECU knows when to shift.
........basically, don't to anything that might be fun and your mileage will go up.
Oh, and DO NOT hold in the clutch and coast.... *if* you save $20 over the next 5,000 miles it'll be offset by needing to replace your clutch that much sooner.
11-09-2004, 04:14 AM
#6
Guest
Posts: n/a
Originally Posted by 2k2wannabe
Oh, and DO NOT hold in the clutch and coast.... *if* you save $20 over the next 5,000 miles it'll be offset by needing to replace your clutch that much sooner.
11-09-2004, 04:53 AM
#9
Guest
Posts: n/a
Originally Posted by bgates1654
Holding your clutch in all the time will cause your throw out bearing to wear out quickly.
and I was asking so people here at work about 2k2wannabe's post, and one guy said the throw-out bearing would wear out (like you said) and another said the throw-out bearing is only used when you initially depress the clutch...
hmmm..
I don't know who to believe.
-vq
11-09-2004, 05:14 AM
#10
It's chrome alright...
Join Date: Dec 2001
Posts: 4,009
Originally Posted by vqman
one guy said the throw-out bearing would wear out (like you said) and another said the throw-out bearing is only used when you initially depress the clutch...
-vq
-vq
11-09-2004, 06:42 AM
#11
do not ride the clutch or place it in neutral for a long time. this can screw up either the clutch or the tranny, or both. if you want to save gas just drive steadily, no fast acceleration. driving at higher speeds doesnt make that much difference, and anything that says so is just propaganda. i was reading and autozone thing on gas mileage and it said that "you use 17% more fuel at 75 than 65" think about this and do the math it doesnt mean $#it because you are traveling 15.4% faster, a 1.6% loss. so if you get 20mpg @65 you will get 19.68mpg @75. whats your time worth?
seriously, acceleration requires energy. constant velocity does not. its simple physics. if you keep constant speed all you have to overcome is friction with the road and wind resistance.
seriously, acceleration requires energy. constant velocity does not. its simple physics. if you keep constant speed all you have to overcome is friction with the road and wind resistance.
11-09-2004, 07:14 AM
#12
Sometimes cruise control also decreases milage when you're on hilly roads. This is because the cruis is trying to maintain speed while going up the hill making the car think it's actually ecellerating. If you slow a little while going up and then bring it back to speed while going down, you should save a good deal of gas. The only problem is that you'll have guys like me on your bumper all the way up the hill!
11-09-2004, 07:33 AM
#13
Maxima Pilot
Join Date: Oct 2001
Location: Beaverton, Oregon
Posts: 1,467
Originally Posted by Matt_01SE_20th
do not ride the clutch or place it in neutral for a long time. this can screw up either the clutch or the tranny, or both.
One more suggestion for improving fuel mileage: get your dealer to bump up the timing to +17 BTDC -worth at least a half-mile per gallon
11-09-2004, 08:05 AM
#14
Originally Posted by 2k2wannabe
Never go above 3k rpm.
Never floor it.
Shift as soon as you can, and keep it in the highest gear possible.
Use a/c as little as possible, and only above 40mph.
Never floor it.
Shift as soon as you can, and keep it in the highest gear possible.
Use a/c as little as possible, and only above 40mph.
if I really wanna save gas, I just shift before 3000 rpms.... on the highway, I'll get into 6 and just cruise at around 65 mph... And yeah... it won't be "fun" driving at all cuz then I also never get to hear my intake at 4500 rpms.... it really does save gas though....
11-09-2004, 08:33 AM
#15
It's chrome alright...
Join Date: Dec 2001
Posts: 4,009
Originally Posted by Matt_01SE_20th
driving at higher speeds doesnt make that much difference, and anything that says so is just propaganda.
The energy needed to push the car increases exponentially as the speed increases linearly. You use more gas the faster you go, even if you're going a constant speed, because you have to keep the car moving and the car has to push that much more air out of the way.
road load power = av + bv^2 + cv^3
The letter v represents the velocity of the car, and the letters a, b and c represent three different constants:
(read more about it here: )
http://auto.howstuffworks.com/question477.htm
The most important part:
But the bottom line is, if you double your speed, this equation says that you will increase the power required by much more than double. A hypothetical medium sized SUV that requires 20 horsepower at 50 mph might require 100 horsepower at 100 mph.
11-09-2004, 08:46 AM
#16
Originally Posted by KabirUTA13
ya basically i need more gas mileage... wat can i do other than oil change and air filter
Maxima is not an economy car, but does pretty darn good for a fairly large family sedan with the power it has, if you just drive sensibly and maintain your car properly.
11-09-2004, 09:09 AM
#17
all i am saying is that most of those little tips that say drive slower are in some way not all true. i agree with what you are saying 2k2wannabe, and i am a mechanical engineer so i am familiar with the energy load equations and how and why they work. but when i drive on long trip i typically do between 80 & 90 and get about 26mpg, when i do 65 i get about 27.5mpg. all i am saying is that i would rather get there faster than save a buck or two on gas. people just tend to make it seem like that equation is so much larger
anyway just remember to look more closely at the numbers some of those gas saving tips throw out. and remember, acceleration is what really kills you
anyway just remember to look more closely at the numbers some of those gas saving tips throw out. and remember, acceleration is what really kills you
11-09-2004, 09:13 AM
#18
I have an 01 auto. It was giving me 22mpg.. I got tired of having to fill the car every two days.. I drive over a 100 miles per day. I bought my wife a new 05 Camry and kept the old car we had. It is a Corolla with 111k miles on it, and is giving 34 mpg driving at 70 to 80 mph. So I think it is extremely GREAT, Ahh the car is a 94. I'm keeping this baby until it explodes.. My Max is in the GARAGE and will stay there until the GAS price comes down. Too much $2.27 in Central Florida.
To answer your question.. there is almost nothing you can do. Normally the Max is a gas drinker.. so try to drive under 55, regular maintenance ( tune up and check your tires...for the resthave fun driving..
To answer your question.. there is almost nothing you can do. Normally the Max is a gas drinker.. so try to drive under 55, regular maintenance ( tune up and check your tires...for the resthave fun driving..
11-09-2004, 09:17 AM
#19
It's chrome alright...
Join Date: Dec 2001
Posts: 4,009
Originally Posted by Matt_01SE_20th
all i am saying is that most of those little tips that say drive slower are in some way not all true ... anyway just remember to look more closely at the numbers some of those gas saving tips throw out. and remember, acceleration is what really kills you
All? No. Nothing is "all true" but I'd rather go 73 and get 30mpg than go 88 and get 25mpg.... and if you get a ticket for speeding, all the time you saved by speeding is going to get eaten up while you're pulled over waiting for the cop to write the paperwork.... and then there's the $$.
But we all make choices.
11-09-2004, 09:37 AM
#20
Originally Posted by Matt_01SE_20th
all i am saying is that most of those little tips that say drive slower are in some way not all true. i agree with what you are saying 2k2wannabe, and i am a mechanical engineer so i am familiar with the energy load equations and how and why they work. but when i drive on long trip i typically do between 80 & 90 and get about 26mpg, when i do 65 i get about 27.5mpg. all i am saying is that i would rather get there faster than save a buck or two on gas. people just tend to make it seem like that equation is so much larger
anyway just remember to look more closely at the numbers some of those gas saving tips throw out. and remember, acceleration is what really kills you
anyway just remember to look more closely at the numbers some of those gas saving tips throw out. and remember, acceleration is what really kills you
11-09-2004, 10:03 AM
#22
Originally Posted by Matt_01SE_20th
do not ride the clutch or place it in neutral for a long time. this can screw up either the clutch or the tranny, or both. if you want to save gas just drive steadily, no fast acceleration. driving at higher speeds doesnt make that much difference, and anything that says so is just propaganda. i was reading and autozone thing on gas mileage and it said that "you use 17% more fuel at 75 than 65" think about this and do the math it doesnt mean $#it because you are traveling 15.4% faster, a 1.6% loss. so if you get 20mpg @65 you will get 19.68mpg @75. whats your time worth?
seriously, acceleration requires energy. constant velocity does not. its simple physics. if you keep constant speed all you have to overcome is friction with the road and wind resistance.
seriously, acceleration requires energy. constant velocity does not. its simple physics. if you keep constant speed all you have to overcome is friction with the road and wind resistance.
"driving at higher speeds doesnt make that much difference, and anything that says so is just propaganda" & "if you keep constant speed all you have to overcome is friction with the road and wind resistance"
I copied and pasted your quotes above. You kinda contradicted yourself by making those statements. Wind resistance, road friction, and higher RMPs speed (depend on the gearing) WILL significantly reduce the gas mileage of any car. Since the Maxima's body shape is somewhat aerodynamic (rated in the low 30's in coeff. of drag), it does help to a point. Much more energy is required from the engine to overcome the wind resistance and road friction as the speed increases above 50mph. IMO, The key to achieve a good gas mileage is in the gearing of the transmission. For a manual, try upshift the transmission to a higher gear as early as possible.
11-09-2004, 11:33 AM
#23
2k2 wannabe: i agree with waht you are saying but like you said, if you follow all 5 tips you get 5mpg. basically what i am saying is that the "lower your speed" one is the one that offers the lowest gains. i always say "to each thier own" and like you pointed out, there is downsides to the way i do it but it is my preference & i think its worth the trade off.
bigfly: i believe that you have looked at the numbers on this and i believe you have posted true numbers. however in my experience the difference is not that great. maybe a difference is the 3L vs. the 3.5L, or the transmission gearing (i have a 5-speed, if you have auto that might explain some of the difference), and i am sure there are a bunch of other things that may go into it. the #'s i posted were just my personal experience and my feelings on the issue based on those experiences.
VMaximus: i am both a working engineer and a student. i am in a co-op program. as per the topic at hand, i am just trying to say that the gains, in my experience, are not that great going 65 as opposed to 75 or 85. like stated above, there are alot of different variables in fuel mileage figures. as for what you said is a good way to get good fuel mileage, spot on. higher gears will give you better fuel mileage, as will shifting early. this is like what i said before about not accelerating fast. the situation i got my numbers from is my frequent trip between detroit and chicago, where i hop on I-94 and cruise at 80-90 for 230 miles. it is a trip i make alot and i have found very little difference between 70(the speed limit) and 85.
bigfly: i believe that you have looked at the numbers on this and i believe you have posted true numbers. however in my experience the difference is not that great. maybe a difference is the 3L vs. the 3.5L, or the transmission gearing (i have a 5-speed, if you have auto that might explain some of the difference), and i am sure there are a bunch of other things that may go into it. the #'s i posted were just my personal experience and my feelings on the issue based on those experiences.
VMaximus: i am both a working engineer and a student. i am in a co-op program. as per the topic at hand, i am just trying to say that the gains, in my experience, are not that great going 65 as opposed to 75 or 85. like stated above, there are alot of different variables in fuel mileage figures. as for what you said is a good way to get good fuel mileage, spot on. higher gears will give you better fuel mileage, as will shifting early. this is like what i said before about not accelerating fast. the situation i got my numbers from is my frequent trip between detroit and chicago, where i hop on I-94 and cruise at 80-90 for 230 miles. it is a trip i make alot and i have found very little difference between 70(the speed limit) and 85.
11-10-2004, 01:31 AM
#25
trust me... driving 65 vs 80 or even 85 mph will be a big difference. I drove from my girlfriend's place to Las vegas at 65 mph and got spent about a line and a half tank. The trip was approximately 245 miles. By the time i hit half tank, i was amazed that I hit 300miles!
But yes, acceleration does affect gas significantly. I still switch gears at 2k rpm and I am a dog, but my gas mileage still suks.
But yes, acceleration does affect gas significantly. I still switch gears at 2k rpm and I am a dog, but my gas mileage still suks.
11-11-2004, 08:43 AM
#29
get an intake, i have the injen knock off from ebay, it was good for 1.5-2 mpg, definatly worth the $$. Also get an exaust if you want to do better, y-pipe, catback and intake was good for a solid 4mpg hwy gain on my 2k se.
you still have to lay off the acelerator though.......
you still have to lay off the acelerator though.......
11-11-2004, 08:50 AM
#31
from a while back...
Originally Posted by budha56
I have this on my computer...I think I copied it from the FAQ's? Anyway, you can try these things:
Low gas mileage can come from any number of places. Let's start with the basics. Keep in mind the following for optimal gas mileage: use 91+ octane fuel, try to keep RPMs below 4k (normal), your car must be in overall good working order (good oil, good coolant etc) and other factors. If you're doing a bunch of 5 minute trips, or its 0 degrees outside, don't expect gas mileage to be so hot. Also keep in mind that different types of gas can have an effect on the mileage. Shop around to find the best gas you can. But if none of these describes your preidcament, read on. Below are some common causes and cures for bad gas mileage.
1) Air filter. The stock filter on the car is a drop in panel filter. If you bought your car used there is a chance that the filter may have never be changed. This would be the time to do it and you have several options: drop in K&N filter, cone filter or CAI. A search on any of these terms will resolve any questions you may have. If you have a cone filter, the filter may be dirty. K&N makes a recharge kit that is available at Pepboys to clean the filter.
2) Fuel filter. The fuel filter is small gray cylinder on the back of the firewall that is to be changed on a 60k service interval. It is often to blame for bad gas mileage, but can be a pain in the butt to change, but it can be done. The filter is relatively cheap from Nissan. Some members reccomend buying a fuel filter for a Nissan 300ZX. Its the same size hoses, but twice the size, so it lasts 2x longer and is doubly effective. The choice is up to you. The writeup to change the filter can be found here: www.maximadriver.com
3) Spark plugs. If you're running anything other than NGK plugs in your engine, or you bought your car used, go get some NGK spark plugs for the dealer. Spark plugs are to be repalced every 60k miles, but rarely are. They will cost about $10 a pop. Sprintmax has a great spark plug changing writeup that can be found here: http://www.sprintmax.com/tails/sparkplug.htm
4) Dirty throttle body. The throttle body is the first piece of metal behind the intake system. It accumulates a certain amount of dirt and grime. Those who clean it out after long neglect find their car is smoother and that fuel economy does increase. Writeup can be found here: www.motorvate.ca
5) Tire Pressure. Stock tire pressure is 29psi. I found recently that mine were at 25 and filled them up and found a substantial increase in fuel economy. If your tires are low, go ahead and fill them up (I filled to about 31, but everyone has a preference).
6) Oxygen sensors. If an oxygen sensor is messed up, it will trigger a Check Engine Light. There are three sensors in total. 2 rest in the respective branches of the Y Pipe (these are the Front Heated 02 Sensors) and one rests in the catalytic converter (95-96) or in the B Pipe right behind the cat (97-99). If any of these sensors fail, gas mileage will decrease substantially. Many sites exist that sell oxygen sensors (dealers will charge a lot). www.buyoxygensensors.com gets good reviews on this site frequently, and they have good prices. For a writeup, go to www.motorvate.ca, or search around the .org
7) Knock Sensor. This is the bad boy, the code everyone fears. The sensor is actually just a piece of metal that rests under your intake manifold. They cost approximately $110 from various sources (www.thepartsbin.com is usually cited as one of the best). The sensor is not terribly difficult to change, but as my friend Harold described it, "Nissan must weld razor blades under the manifold." Due to tight fitting, the sensor often results in a bloody hand. The writeup for the sensor can be found at www.motorvate.ca
8) Dirty fuel system. As a car grows older, carbon deposits in the fuel path, clogging areas such as the injectors. Many modern gasolines are designed to combat this (such as Chevron with Techron) and there are many additives that can be added to gas to clean out these systems. Many mechanics offer a full fuel system clean out for about $50-$75. Many .orgers believe this to be BS, some think the process is valid. The choice is yours.
This is the ticket to good gas mileage! Any other questions can be resolved using the search function, as this subject is discussed quite often. Enjoy!
Last edited by gepetto on 01-07-2003 at 03:37 PM.
Low gas mileage can come from any number of places. Let's start with the basics. Keep in mind the following for optimal gas mileage: use 91+ octane fuel, try to keep RPMs below 4k (normal), your car must be in overall good working order (good oil, good coolant etc) and other factors. If you're doing a bunch of 5 minute trips, or its 0 degrees outside, don't expect gas mileage to be so hot. Also keep in mind that different types of gas can have an effect on the mileage. Shop around to find the best gas you can. But if none of these describes your preidcament, read on. Below are some common causes and cures for bad gas mileage.
1) Air filter. The stock filter on the car is a drop in panel filter. If you bought your car used there is a chance that the filter may have never be changed. This would be the time to do it and you have several options: drop in K&N filter, cone filter or CAI. A search on any of these terms will resolve any questions you may have. If you have a cone filter, the filter may be dirty. K&N makes a recharge kit that is available at Pepboys to clean the filter.
2) Fuel filter. The fuel filter is small gray cylinder on the back of the firewall that is to be changed on a 60k service interval. It is often to blame for bad gas mileage, but can be a pain in the butt to change, but it can be done. The filter is relatively cheap from Nissan. Some members reccomend buying a fuel filter for a Nissan 300ZX. Its the same size hoses, but twice the size, so it lasts 2x longer and is doubly effective. The choice is up to you. The writeup to change the filter can be found here: www.maximadriver.com
3) Spark plugs. If you're running anything other than NGK plugs in your engine, or you bought your car used, go get some NGK spark plugs for the dealer. Spark plugs are to be repalced every 60k miles, but rarely are. They will cost about $10 a pop. Sprintmax has a great spark plug changing writeup that can be found here: http://www.sprintmax.com/tails/sparkplug.htm
4) Dirty throttle body. The throttle body is the first piece of metal behind the intake system. It accumulates a certain amount of dirt and grime. Those who clean it out after long neglect find their car is smoother and that fuel economy does increase. Writeup can be found here: www.motorvate.ca
5) Tire Pressure. Stock tire pressure is 29psi. I found recently that mine were at 25 and filled them up and found a substantial increase in fuel economy. If your tires are low, go ahead and fill them up (I filled to about 31, but everyone has a preference).
6) Oxygen sensors. If an oxygen sensor is messed up, it will trigger a Check Engine Light. There are three sensors in total. 2 rest in the respective branches of the Y Pipe (these are the Front Heated 02 Sensors) and one rests in the catalytic converter (95-96) or in the B Pipe right behind the cat (97-99). If any of these sensors fail, gas mileage will decrease substantially. Many sites exist that sell oxygen sensors (dealers will charge a lot). www.buyoxygensensors.com gets good reviews on this site frequently, and they have good prices. For a writeup, go to www.motorvate.ca, or search around the .org
7) Knock Sensor. This is the bad boy, the code everyone fears. The sensor is actually just a piece of metal that rests under your intake manifold. They cost approximately $110 from various sources (www.thepartsbin.com is usually cited as one of the best). The sensor is not terribly difficult to change, but as my friend Harold described it, "Nissan must weld razor blades under the manifold." Due to tight fitting, the sensor often results in a bloody hand. The writeup for the sensor can be found at www.motorvate.ca
8) Dirty fuel system. As a car grows older, carbon deposits in the fuel path, clogging areas such as the injectors. Many modern gasolines are designed to combat this (such as Chevron with Techron) and there are many additives that can be added to gas to clean out these systems. Many mechanics offer a full fuel system clean out for about $50-$75. Many .orgers believe this to be BS, some think the process is valid. The choice is yours.
This is the ticket to good gas mileage! Any other questions can be resolved using the search function, as this subject is discussed quite often. Enjoy!
Last edited by gepetto on 01-07-2003 at 03:37 PM.
11-11-2004, 09:13 AM
#32
last night myth-busters concluded that A/C actually makes lower MPG than the indows down at high speeds.
but they also used a Ford Explorer. I would hope we have better engineering.
Well I have the nice little feature of MPG on my display. I'm sure this isn't accurate to the .1 mile, but it is close (compare to my calculations at fill up) and good for comparisons.
Cruising at 55-60 (very hard to do) it read 32 mpg once it settled/averaged after a few miles. When I got to a comfortable 85, it dropped to 27 mpg. both times I waited to reset it until I was already cruising at the speed. if coasting (almost no throttle) it can read 50 mpg before it averages more accurately. when accelerating, it can read 10 mpg.
I hardly drive highways (everything is 10 min from my house) and average 20 mpg. rated 19/29. highway trips are often +/- 30
I always roll to a stop and never idle in the morning. Drive low RPM to warm car saves a lot of gas.
but they also used a Ford Explorer. I would hope we have better engineering.
Well I have the nice little feature of MPG on my display. I'm sure this isn't accurate to the .1 mile, but it is close (compare to my calculations at fill up) and good for comparisons.
Cruising at 55-60 (very hard to do) it read 32 mpg once it settled/averaged after a few miles. When I got to a comfortable 85, it dropped to 27 mpg. both times I waited to reset it until I was already cruising at the speed. if coasting (almost no throttle) it can read 50 mpg before it averages more accurately. when accelerating, it can read 10 mpg.
I hardly drive highways (everything is 10 min from my house) and average 20 mpg. rated 19/29. highway trips are often +/- 30
I always roll to a stop and never idle in the morning. Drive low RPM to warm car saves a lot of gas.
11-11-2004, 10:00 AM
#36
Member
Join Date: Nov 2004
Posts: 76
Originally Posted by Matt_01SE_20th
i was reading and autozone thing on gas mileage and it said that "you use 17% more fuel at 75 than 65" think about this and do the math it doesnt mean $#it because you are traveling 15.4% faster, a 1.6% loss. so if you get 20mpg @65 you will get 19.68mpg @75. whats your time worth?
Lets say that you are travelling 65mph at 20mpg for one hour.
IF you are spending 20mpg, you will have spent: 65mi/20mpg=3.25 Gallons.
According to your 17% Autozone theory above, we will have spent 17% more, or 3.25*1.17=3.8025 gallons to go 65 miles at 75 miles per hour. Thus going 75 miles per hour and spending 3.8025 gallons after 65 miles we get: 65m/3.8025gallons = 17.094 mpg @75mph
Going 75 miles per hour, we will have travelled 65 miles in 52 minues, as opposed to 60 minutes going 65 miles per hour. A time savings of 8 minutes or 13.33%.
If your 17% theory is true, you will have spent .5525 gallons extra to save 8 minutes for every hour you are driving at 75mph versus 65mph. Of course this is all based on the 17% theory and that you are originally getting 20mpg@65mph.
Now you are correct in asking how much your time is worth. With gas prices these days, .5525 gallons will cost you about a dollar. For a 195 mile trip, or 3 hours going 65mph, going 75mph will save 24 minutes but you will spend an extra 3 bucks. How much is your time worth?
Also after reading the previous posts it was said that holding the clutch wears out the throwout bearing. Although this is relatively true, I wouldn't worry so much about the throw-out bearing as much as the pilot shaft(the shaft that the throwout bearing sits on). The act of pressing, and de-pressing the clutch will wear out your pilot shaft . For instance, holding in your clutch for 10 minutes will not hurt anything (may wear out your throwout bearing a bit), but the act of pushing the clutch in and out a thousand times a day is far worse. Replacing a pilot shaft is much more expensive than replacing the throwout bearing, which only cost a couple of bucks and is normally replaced when the clutch is replaced. Some trannies have the pilot shaft casted with the bell housing, so replacing the pilot shaft will require a tranny rebuild. That really sucks. The slightest wear on the pilot shaft will cause the throwout bearing to push on the clutch fingers unevenly. This will cause your clutch disk to wear out unevenly and much quicker. You will also feel alot of vibration when letting out on the clutch.
In conclusion, going faster does spend more gas, but saves you time. It's up to you to determine if it's worth it. Also avoid unnecessary engaging and dis-engaging of the clutch. just my .02
11-11-2004, 03:02 PM
#37
Member
Join Date: May 2003
Posts: 96
I get better milage with my Frankencar intake and Apexi filter. I am averaging 23.5 over the last 20K. And I drive alot. And sometimes fast. At times I'll coast in neutral even though I've got auto, but not often, it's too flat around here. And you can turn off and on the A/C ( well I'm in Florida and most people are still running it full-time! ) But I noticed that only part time A/C saves gas too.
11-11-2004, 07:03 PM
#38
Originally Posted by MaxOctane
I'm not sure what kind of math or engineering you are practicing, but you cannot make the time/mpg conversion you just made - at least not in this universe.
Personally, not having read the Autozone article, I find it hard to believe that they would equate fuel consumption per unit of time as opposed to fuel consumption per distance travelled. I suspect what they were trying to say was that if you travel the same distance at 65mph and at 75mph, you will used 17% more fuel to get there going 75mph.
11-11-2004, 08:34 PM
#39
Member
Join Date: Apr 2003
Posts: 63
Originally Posted by BigFly_2K2SE
I believe the "math" that Matt was doing with the 17% theory from Autozone was that he was saying that the car uses 17% more fuel per unit of time at 75mph than 65mph. Therefore, once you factor time into the equation (15.4% less travel time at 75 than 65), it amounts to basically no more fuel used.
Personally, not having read the Autozone article, I find it hard to believe that they would equate fuel consumption per unit of time as opposed to fuel consumption per distance travelled. I suspect what they were trying to say was that if you travel the same distance at 65mph and at 75mph, you will used 17% more fuel to get there going 75mph.
Personally, not having read the Autozone article, I find it hard to believe that they would equate fuel consumption per unit of time as opposed to fuel consumption per distance travelled. I suspect what they were trying to say was that if you travel the same distance at 65mph and at 75mph, you will used 17% more fuel to get there going 75mph.
Ummm....Unless someone somewhere puts a value on time (time=some dollar amount) then no, you can't factor time into that equation. As for me, I travel 150 miles to work. If I drove 65 the entire way I would most definitely fall asleep so I have set my time value quite high. Thus 75 all the way for me. Keeps me on my toes and AWAKE at least.
11-12-2004, 05:51 AM
#40
Member
Join Date: Sep 2004
Posts: 97
Now with an identical car you can factor out Coefficient of drag, density, and area. You are left with D = (V^2)/2
A car travelling at 40mph will have a (V^2)/2 value of 800.
A car travelling at 80mph will have a (V^2)/2 value of 3200.
Thus the equations show that when your speed doubles, the aerodynamic drag quadruples.
A car travelling at 60mph will have a (V^2)/2 value of 1800
A car travelling at 70mph will have a (V^2)/2 value of 2450
The increase in drag from 60mph to 70mph is 36%
The increase in drag from 70mph to 80mph is 31%
The increase in drag from 60mph to 80 mph is 77%
Conclusions: Your car, while consuming more fuel at higher speed is also having to work harder to maintain its speed, thus lower speed is better, but only to a point. This is dependant on the fuel map and how much fuel it consumes at each rpm as well as your gearing. The rule of thumb is 55mph for best gas mileage, but I experienced great gas mileage (would have gotten ~500 miles out of tank) going 75-78 on the highway in my auto. Slowing down and accelerating, even from 60 to 80 on the highway will kill your gas mileage, as I also experienced on the same trip.