@ratekin: Yeah, I've been doing that since my very first car, but when I moved, and switch to a 6.1L V8 and E85 and realized I was slightly above 8MPG city (in winter, in Massachusetts), it all went south, so I stopped.
Also, one more thing that you could mention is the transmission: is it auto? Cause the auto with torque converter are terrible for fuel economy (especially in town). Though I'd guess from your numbers, it's manual.
@Greg818: My transmission is an auto, and my car is rated at 25 city / 35 Hwy. I drive about 70% highway / 30% city, but higher speeds reduce my mpg to around 30-31 most of the time.
Also, there's a German site that will help you with that: Spritmonitor.de. It will even allow you to compare yourself to other identical cars, and so what they did. You can log absolutely everything, which I used to do, including the cleaning products and all.
I used to use it about 10 years ago, but I gave up altogether, because... I don't really give a rat's ass anymore. I mean, I do what I can to maximize my fuel economy, I even found myself hypermiling... but I don't to track it that anymore.
I drive a 94 Nissan Maxima (17 city, 23 highway). I don't watch stuff like how much gas I'm buying over the course of a year or how much it costs, I keep an eye on it per tank. Something I've noticed is that the faster I go the better mileage I get out of it. 90mph leaves my engine at the same RPM as 60-65mph. While I'm risking a ticket, I'm getting a ton of extra distance out of my tank of gas.
And while I'm ashamed to say it's an automatic, I try to drive like it's a manual, letting off the gas to encourage it to shift earlier. Combined with driving faster and keeping an eye on the tachometer I've squeezed out 28-29 MPG on the last 3 tanks of gas.
Well, all I know for sure is that last year I chugged down roughly 6 cubic meter of gasoline for a little over 35,000 miles (altogether), so it's not that bad considering each car contribution and EPA rating.
Also, one thing that has a LOT of impact and that is very often overlooked is tire pressure, mine are always pumped as high as the tire is rated for (except specific use, or discomfort).
Also, for most small cars (sub compacts), usually the best fuel economy is achieved at around 65-70MPH, beyond that not only does the engine run a tad too high for good fuel economy, but the drag coefficient makes things much worse. @Toxeia: So, 90MPH seems a tad (lot!) high, have you tried 70-75? Also are those numbers the onboard computer's numbers or added gas and distance travelled.
Also, one fun thing to do to improve your millage if your not in a flat state: gather speed (try to stay reasonable) in downhills and let it slow down gradually in uphills. Doing so I achieved 53.5MPG city with a car rated around 28MPG city (european 2L turbo diesel w/ manu).
Also, auto trannies aren't all that bad, the ones that aren't too good are the ones with torque converter (actually pretty much everything with auto tranny in the US) because they've got a constant slip and all and I'm not gonna go into details too much, but rule of thumb: dual clutch auto = Good, otherwise you're F'ed!
@Toxeia said:
I don't watch stuff like how much gas I'm buying over the course of a year or how much it costs.
@Greg818: Well from 65 to 90, it's all the same on the tachometer, and I do use less gas (evidenced by trip odometer). So anything above 65 is more fuel efficient, just seems that 90's the most efficient my car can get. State troopers would disagree though, I'm sure.
@Toxeia: What's the penalty for doing 90 MPH where you are? Where I live (Ontario), doing the equivalent of 30 MPH over the limit could get your license suspended for 2 years, and/or 6 months of jail time, and/or a $10,000 fine. Probably not worth the risk to save a bit of gas.
@Toxeia: Darn, that's hard to believe as I had to do extensive testing on many different cars (engine size/layout, transmissions...) and pretty much all cars were the most efficient around 60-65MPH (trucks better around 50-55 depending on gearing a lot more than cars).
Even my Mustang GT with the 3.31 rear axle, which turns in about 1,300RPM@65MPH isn't better over 65.
I'm not implying anything other than, well, that's an odd case, really. Now I'm a lot more curious about your car. What's the engine speed at 90MPH? Do you have any idea about the mileage at that speed? It's a 4 gears right? Is there some weird overdrive shit in the mix? What tires do you have in it (brand, model and dimensions)? Do you know how much it weights?
I'm curious because at 90MPH, there are only a few cars that aren't too penalized but their drag coefficient (Prius and Merc E class come to mind), plus tires are starting to really slow the car down at that speed (there's a wave that propagates on the tire, and the faster you go, the more resistance it opposes). That (your car's case) is very interesting (well, for me at least)!
I have kinda been paying attention to how my '01 VW Jetta VR6 does in comparison to my crappy old '92 Chevy Cavalier. My Jetta's rated at 12.6 L/100KM for city and 8.4 L/100KM on the highway and that seems about right. It is automatic. I wanted manual but my dad got me a sick deal on this car so I couldn't pass it up. I only paid $2000 for it and the only issues have been one worn out strut, which was like $300 to replace, and a coolant leak, which is getting addressed on Monday and will likely be around $300 again (this is a very common issue on these engines so it will be a fairly simple fix because I've already identified exactly what is leaking). It doesn't burn oil and it runs silky smooth. My tank is 55 litres and it lasts me about 3-4 weeks, which isn't bad because my work commute is 14 KMs each way, half of which is on the highway.
I imagine it will last an extra day or two once summer is done and I can turn off the AC (my VW is black exterior with black interior and this summer has been insanely hot so having AC off isn't an option, especially when I get out of work at the hottest part of the day). It trounces my old Cavalier in terms of mileage, which is the opposite of what I thought would happen given that my Cavalier was much lighter and had a small 4-cylinder engine rather than the beefier 6-cylinder in my VW, which also weighs 500 pounds more.
@Ben_H: Why wouldn't you use the AC? If it's for fuel economy, it usually is just background noise if everything is working properly, especially on "bigger" engines. Also, having the windows down will definitely decrease your milage, especially at highway speeds. Also, when it's really toasty outside, using the AC isn't too bad because it forces the engines fan to run permanently (on low speed).
@Ben_H: Why wouldn't you use the AC? If it's for fuel economy, it usually is just background noise if everything is working properly, especially on "bigger" engines. Also, having the windows down will definitely decrease your milage, especially at highway speeds. Also, when it's really toasty outside, using the AC isn't too bad because it forces the engines fan to run permanently (on low speed).
Yeah that makes sense now that I think about it. I'm just saying that I basically haven't turned it off since I got the car since it has been 25 Celcius or more almost every day since I got the car and I wonder if having AC off will make a difference (my dad said it will be negligible too). I guess I just associate how AC works with my old car, which had a rather weak engine and AC did have a noticeable effect on performance. That thing was downright gutless feeling when AC was on, though it had electrical issues, among other problems from when I got it until I sold it.
@Greg818: Well from 65 to 90, it's all the same on the tachometer, and I do use less gas (evidenced by trip odometer). So anything above 65 is more fuel efficient, just seems that 90's the most efficient my car can get. State troopers would disagree though, I'm sure.
I'm not saying you are lying or anything but I don't see how that's possible. There is more drag on your car the faster you go. It's why you need a ridiculous amount of horsepower once you get into the 200 MPH range. It's all about overcoming the resistance from the air. Maybe 65 to 90 isn't significant enough of a change, who knows. Looks like we came up with a Mythbusters episode.
I don't think need to shoot bowling balls through two houses and two cars...
It might just be that the gearing is very long, and the torque converter is wasting a lot at 65, and then at 90, then clutch is coupled too, so less loss. But it would only be true if it's a TC+Clutch, which I have no idea if the Maxima is.
@CROM: You never popped up in my notification thing =(
In Texas it's pretty much up to the city you're caught in. While I can't find any references to my town of residence, a few major cities in the state of Texas will fine you $300 for going 30mph over the speed limit. San Antonio specifically charges you $166 for the first 10, and $5 for every mile over.
As for losing your license, speeding won't do it. You'd have to have a pretty bad accident or be a repeat DWI offender to have your license suspended or revoked. In Texas we have a point system. Speeding get you 2 points, speeding and causing an accident 3. If within 3 years you get 6 points, you're charged an annual $100. For every point beyond that you pay an extra $25 to keep your license. If you behave, you'll lose points and have to pay less. If you get back under 6, you aren't charged anything beyond regular fees.
@grimace73: I totally agree. It doesn't make sense to me either. From what I remember in school, something like 80% of your fuel consumption goes towards defeating wind resistance. I have no idea why speeding gets me better mileage.
I drive a 94 Nissan Maxima (17 city, 23 highway). I don't watch stuff like how much gas I'm buying over the course of a year or how much it costs, I keep an eye on it per tank. Something I've noticed is that the faster I go the better mileage I get out of it. 90mph leaves my engine at the same RPM as 60-65mph. While I'm risking a ticket, I'm getting a ton of extra distance out of my tank of gas.
And while I'm ashamed to say it's an automatic, I try to drive like it's a manual, letting off the gas to encourage it to shift earlier. Combined with driving faster and keeping an eye on the tachometer I've squeezed out 28-29 MPG on the last 3 tanks of gas.
That's not physically possible, having the same RPM at two different speeds, unless you are towing something. You can't go two different speeds at the same RPM. The only way to do this is to put a much higher load on the engine, towing or loading your car down with a lot of weight (stuffing it full inside), and you will never get a higher fuel economy at a higher speed by putting a bigger load on your engine. Towing something at 70 mph in my truck takes about the same RPM as it being empty, but the engine is doing a lot more work and burning more fuel. What you're suggesting is literally impossible.
EDIT: Actually you can do this, but only, and I mean only if you are removing a tremendous amount of weight from your car to go 90 versus 60-70 mph. I seriously doubt you are doing that though.
From what I remember in school, something like 80% of your fuel consumption goes towards defeating wind resistance. I have no idea why speeding gets me better mileage.
Well, that is true at ONE point (i.e. at one given speed). Fro instance, for most cars (by cars I mean vehicles with car weight, car tires, car size and car weight, so no donk or stuff like that), the loss in the driveline+tires is about equal to drag induced loss at around 25MPH.
@HKZ said:
That's not physically possible, having the same RPM at two different speeds.
Man, I'm trying to understand, but I just can't figure out what you meant, because I'm pretty sure that it's not what you meant. Also, I just can't follow your logic on the weighting stuff, really, just can't figure out what you mean here either.
Also, at high speeds, mass doesn't have a great impact on fuel economy, unless you're going uphill...
That's not physically possible, having the same RPM at two different speeds while in the same gear.
That's how I understand it at least.
And yeah, I'm not able to figure it out, but at 55 it's at 2k RPM, at 65 it gets to 2.2-2.3, and then it stays there until 90. I'd say the gauge was busted, but it shows up in the mileage for that tank of gas.
@Toxeia: That's what I meant, thanks for the correction. You cannot go two different speeds at the same RPM without more or less engine load. It cannot be done. There are fixed ratios in every modern car transmission and the laws of physics dictate that to go 65 mph with one engine speed you can't go another engine speed with the same RPM unless the loading on the engine is different. Changing the load on the engine, more or less load, impacts fuel economy. You can't get the same economy at two different speeds at the same RPM, the engine load is being changed and you are burning more or less fuel. I can cruise at 2k in my truck going 70, but if I load it full of crap and pull a trailer I can also go 70 with the engine turning 2k, BUT the engine load is higher because I'm moving more weight and my economy tanks. Unless your gauge is broken, or you have nothing in your car except what it needs to run you aren't going to get better mielage at a higher speed. I'm guessing your gauge is busted and calculating off of one tank isn't enough to tell you definitively that your mileage is better. That's why I am so harsh on the Mythbusters on here. I've said many times before they don't do real science because the number of variables, especially in their fuel economy tests, are so varied and so important that their testing is null and void because they won't factor them out sufficiently.
@Greg818: Mass does have an effect because no road is perfectly level and you're always going to be changing the engine load. Modern cars are able to lean out their mixture for cruise but even still turning more RPM on a fixed ratio transmission is going to cause fuel consumption to go up. Drag squares with speed, I think that's the correct ratio I may be wrong, so even on a slippery car you're increasing drag every time to increase your speed and so your car engine is doing more work. Turning an engine faster will burn more fuel over time and testing with one or two tanks of fuel isn't going to give you a definitive figure.
Toxiea fixed my statement in his post, I meant that in the same gear you can't physically turn the same RPM at 65 that you are turning at 90. It simply isn't possible because gear ratios are fixed and you can't turn an engine at two different RPM speeds and get the exact same wheel speed. Nissan has put out a few CVT cars but his year model wasn't one of them. Unless he's tucking his mirrors I don't see how it's possible to vary the speed 30 miles an hour faster an get better economy. His car isn't all that slippery and the increased drag on the car will cause fuel consumption to go down. Even slippery cars like the Vette and others will get worse economy with speed simply because of aerodynamic drag. My point about weight was based on your typical road being undulating. My truck can get 18 MPG on a good day. Same road, same traffic, different weight it will have to work harder even on the smallest of inclines and that burns more fuel.
@Toxeia: To put it crudely, overdrive is a two ratio gearbox in series with the actual gearbox. So, it is possible that, while in the same gear (gearbox), if it's an auto overdrive, you can get the same engine speed, that's why I was asking. But cars (as opposed to trucks), will by default always be in overdrive. Now that I think about it, it's the same on trucks as you have the tow/haul mode... But still, 2.2k at 90MPH seams like an unusually long ratio for such a car.
@HKZ: Man, you're mixing up plenty of things here, I don't know if it's in your head, or when your write it down though. Drag is a constant (drag coefficient), thus no matter the speed, it will be the same. But you've got right, simply put, the drag induced force is proportional to the square of the speed.
Also, I didn't say mass had no effect, but much less than drag. At highway speed, constant speed, drag will be more significant, that's one of the reasons why trucks are still the same weight yet more fuel efficient. Well, work on the aerodynamics and engine too (and drive train and all...). Plus when you hitch a trailer you change drag, rolling friction, and weight by a quite a huge margin, so it's really no a good example to take.
And I'm sorry to be a nitpicker again, but I have to disagree about mixture. Cars don't lean out their mixture per se, it's still constricted to the same values because of exhaust temperature (EGT vs mixture forms a bit of a McDonald's M with the dangling part being 14.7), compression ratio, emission restrictions... so in the end they stick to the V part of the M, which doesn't make a lot of difference (though cars sold in the US, that means modern ones, as in emission regulated, car actually go way more on the rich side when floored, compared to what is allowed in Europe).
Anyway, don't have much more time, but drag, at highway speeds, has a lot of influence on fuel economy, more than anything else, that's why the Mercedes E class, can turn in fuel economies better than lighter, less powerful cars, that's why they work so hard on hybrids to lower the drag (and rolling friction), and not so much on the weight (they still do, but put less effort there).
Edit: I do fully agree on myth buster, if they were anywhere near science, well, first they wouldn't even do that show, because they'd already know what to expect, and they wouldn't have so many unexpected results (first that comes to mind for me is the bowling ball incident)
I made an Excel spreadsheet for keeping track of my mileage and costs. I log any maintenance and modifications and it breaks everything down into per month, per year and grand totals. I scan all the receipts into PDF files as well.
I also use an app called aCar. I enter in the maintenance and modification records here too, but it's primarily for keeping track of my fuel use. It generates all kinds of cool stats, graphs and charts if you're into that sort of thing.
@Bane: I use CarCare and it works much the same way. It's pretty neat together all the graphs and whatnot. I get pretty poor mileage in my truck, but it did get a pretty significant increase in mileage after I lowered it. Since my 76 MGB is about done getting siggnificant work done on it, I'm going to get more than twice the mileage, and look cool driving it. Don't know if I'll use the app on it though, not really sure if the odometer is entirely accurate.
@Bane: Nice ride! Do you do a "lot" of off road? Do you know the final drive? Cause that's a neat milage, can only dream about it with the Raptor (just a little 12MPG average in the last 9 months, but quite a bit and sand trails)
Good evening testers;
I've had my car for 18 months, tracking my MPG, price per gallon, etc.
Do you track your car and what other things do you follow?
The big numbers, 45779.6 miles, 1565.43 gallons of gas, $5,701.16 on gas.29.46 MPG average. (2011 ford focus)
I pay 0.1245 cents per mile.
price per gallon Graph
http://www.flickr.com/photos/13554779@N00/7752284646/
MPG Graph
http://www.flickr.com/photos/13554779@N00/7752284520/
@ratekin: Yeah, I've been doing that since my very first car, but when I moved, and switch to a 6.1L V8 and E85 and realized I was slightly above 8MPG city (in winter, in Massachusetts), it all went south, so I stopped.
Also, one more thing that you could mention is the transmission: is it auto? Cause the auto with torque converter are terrible for fuel economy (especially in town). Though I'd guess from your numbers, it's manual.
@Greg818: My transmission is an auto, and my car is rated at 25 city / 35 Hwy. I drive about 70% highway / 30% city, but higher speeds reduce my mpg to around 30-31 most of the time.
@ratekin: No way! Kudos then!
Also, there's a German site that will help you with that: Spritmonitor.de. It will even allow you to compare yourself to other identical cars, and so what they did. You can log absolutely everything, which I used to do, including the cleaning products and all.
I used to use it about 10 years ago, but I gave up altogether, because... I don't really give a rat's ass anymore. I mean, I do what I can to maximize my fuel economy, I even found myself hypermiling... but I don't to track it that anymore.
@ratekin said:
Shouldn't that be 0.1245 dollars per mile, or 12.45 cents.
Really nice information, I can never seem to stay consistent when trying to do this.
I drive a 94 Nissan Maxima (17 city, 23 highway). I don't watch stuff like how much gas I'm buying over the course of a year or how much it costs, I keep an eye on it per tank. Something I've noticed is that the faster I go the better mileage I get out of it. 90mph leaves my engine at the same RPM as 60-65mph. While I'm risking a ticket, I'm getting a ton of extra distance out of my tank of gas.
And while I'm ashamed to say it's an automatic, I try to drive like it's a manual, letting off the gas to encourage it to shift earlier. Combined with driving faster and keeping an eye on the tachometer I've squeezed out 28-29 MPG on the last 3 tanks of gas.
Well, all I know for sure is that last year I chugged down roughly 6 cubic meter of gasoline for a little over 35,000 miles (altogether), so it's not that bad considering each car contribution and EPA rating.
Also, one thing that has a LOT of impact and that is very often overlooked is tire pressure, mine are always pumped as high as the tire is rated for (except specific use, or discomfort).
Also, for most small cars (sub compacts), usually the best fuel economy is achieved at around 65-70MPH, beyond that not only does the engine run a tad too high for good fuel economy, but the drag coefficient makes things much worse. @Toxeia: So, 90MPH seems a tad (lot!) high, have you tried 70-75? Also are those numbers the onboard computer's numbers or added gas and distance travelled.
Also, one fun thing to do to improve your millage if your not in a flat state: gather speed (try to stay reasonable) in downhills and let it slow down gradually in uphills. Doing so I achieved 53.5MPG city with a car rated around 28MPG city (european 2L turbo diesel w/ manu).
Also, auto trannies aren't all that bad, the ones that aren't too good are the ones with torque converter (actually pretty much everything with auto tranny in the US) because they've got a constant slip and all and I'm not gonna go into details too much, but rule of thumb: dual clutch auto = Good, otherwise you're F'ed!
@Toxeia said:
Well... Don't! Cause you'd have a stroke.
@aaronb: You are correct. Thanks.
@Greg818: Well from 65 to 90, it's all the same on the tachometer, and I do use less gas (evidenced by trip odometer). So anything above 65 is more fuel efficient, just seems that 90's the most efficient my car can get. State troopers would disagree though, I'm sure.
@Toxeia: What's the penalty for doing 90 MPH where you are? Where I live (Ontario), doing the equivalent of 30 MPH over the limit could get your license suspended for 2 years, and/or 6 months of jail time, and/or a $10,000 fine. Probably not worth the risk to save a bit of gas.
@Toxeia: Darn, that's hard to believe as I had to do extensive testing on many different cars (engine size/layout, transmissions...) and pretty much all cars were the most efficient around 60-65MPH (trucks better around 50-55 depending on gearing a lot more than cars).
Even my Mustang GT with the 3.31 rear axle, which turns in about 1,300RPM@65MPH isn't better over 65.
I'm not implying anything other than, well, that's an odd case, really. Now I'm a lot more curious about your car. What's the engine speed at 90MPH? Do you have any idea about the mileage at that speed? It's a 4 gears right? Is there some weird overdrive shit in the mix? What tires do you have in it (brand, model and dimensions)? Do you know how much it weights?
I'm curious because at 90MPH, there are only a few cars that aren't too penalized but their drag coefficient (Prius and Merc E class come to mind), plus tires are starting to really slow the car down at that speed (there's a wave that propagates on the tire, and the faster you go, the more resistance it opposes). That (your car's case) is very interesting (well, for me at least)!
I don't currently have a car, so I don't track it. (I am waiting for my car to get built, which looks to have been delayed until early Q4. :()
I have kinda been paying attention to how my '01 VW Jetta VR6 does in comparison to my crappy old '92 Chevy Cavalier. My Jetta's rated at 12.6 L/100KM for city and 8.4 L/100KM on the highway and that seems about right. It is automatic. I wanted manual but my dad got me a sick deal on this car so I couldn't pass it up. I only paid $2000 for it and the only issues have been one worn out strut, which was like $300 to replace, and a coolant leak, which is getting addressed on Monday and will likely be around $300 again (this is a very common issue on these engines so it will be a fairly simple fix because I've already identified exactly what is leaking). It doesn't burn oil and it runs silky smooth. My tank is 55 litres and it lasts me about 3-4 weeks, which isn't bad because my work commute is 14 KMs each way, half of which is on the highway.
I imagine it will last an extra day or two once summer is done and I can turn off the AC (my VW is black exterior with black interior and this summer has been insanely hot so having AC off isn't an option, especially when I get out of work at the hottest part of the day). It trounces my old Cavalier in terms of mileage, which is the opposite of what I thought would happen given that my Cavalier was much lighter and had a small 4-cylinder engine rather than the beefier 6-cylinder in my VW, which also weighs 500 pounds more.
@Ben_H: Why wouldn't you use the AC? If it's for fuel economy, it usually is just background noise if everything is working properly, especially on "bigger" engines. Also, having the windows down will definitely decrease your milage, especially at highway speeds. Also, when it's really toasty outside, using the AC isn't too bad because it forces the engines fan to run permanently (on low speed).
@Greg818 said:
Yeah that makes sense now that I think about it. I'm just saying that I basically haven't turned it off since I got the car since it has been 25 Celcius or more almost every day since I got the car and I wonder if having AC off will make a difference (my dad said it will be negligible too). I guess I just associate how AC works with my old car, which had a rather weak engine and AC did have a noticeable effect on performance. That thing was downright gutless feeling when AC was on, though it had electrical issues, among other problems from when I got it until I sold it.
@Toxeia said:
I'm not saying you are lying or anything but I don't see how that's possible. There is more drag on your car the faster you go. It's why you need a ridiculous amount of horsepower once you get into the 200 MPH range. It's all about overcoming the resistance from the air. Maybe 65 to 90 isn't significant enough of a change, who knows. Looks like we came up with a Mythbusters episode.
@grimace73 said:
I don't think need to shoot bowling balls through two houses and two cars...
It might just be that the gearing is very long, and the torque converter is wasting a lot at 65, and then at 90, then clutch is coupled too, so less loss. But it would only be true if it's a TC+Clutch, which I have no idea if the Maxima is.
@CROM: You never popped up in my notification thing =(
In Texas it's pretty much up to the city you're caught in. While I can't find any references to my town of residence, a few major cities in the state of Texas will fine you $300 for going 30mph over the speed limit. San Antonio specifically charges you $166 for the first 10, and $5 for every mile over.
As for losing your license, speeding won't do it. You'd have to have a pretty bad accident or be a repeat DWI offender to have your license suspended or revoked. In Texas we have a point system. Speeding get you 2 points, speeding and causing an accident 3. If within 3 years you get 6 points, you're charged an annual $100. For every point beyond that you pay an extra $25 to keep your license. If you behave, you'll lose points and have to pay less. If you get back under 6, you aren't charged anything beyond regular fees.
@grimace73: I totally agree. It doesn't make sense to me either. From what I remember in school, something like 80% of your fuel consumption goes towards defeating wind resistance. I have no idea why speeding gets me better mileage.
@Toxeia said:
That's not physically possible, having the same RPM at two different speeds, unless you are towing something. You can't go two different speeds at the same RPM. The only way to do this is to put a much higher load on the engine, towing or loading your car down with a lot of weight (stuffing it full inside), and you will never get a higher fuel economy at a higher speed by putting a bigger load on your engine. Towing something at 70 mph in my truck takes about the same RPM as it being empty, but the engine is doing a lot more work and burning more fuel. What you're suggesting is literally impossible.EDIT: Actually you can do this, but only, and I mean only if you are removing a tremendous amount of weight from your car to go 90 versus 60-70 mph. I seriously doubt you are doing that though.
@Toxeia said:
Well, that is true at ONE point (i.e. at one given speed). Fro instance, for most cars (by cars I mean vehicles with car weight, car tires, car size and car weight, so no donk or stuff like that), the loss in the driveline+tires is about equal to drag induced loss at around 25MPH.
@HKZ said:
Man, I'm trying to understand, but I just can't figure out what you meant, because I'm pretty sure that it's not what you meant. Also, I just can't follow your logic on the weighting stuff, really, just can't figure out what you mean here either.
Also, at high speeds, mass doesn't have a great impact on fuel economy, unless you're going uphill...
@Greg818: Let me fix what @HKZ said:
That's how I understand it at least.
And yeah, I'm not able to figure it out, but at 55 it's at 2k RPM, at 65 it gets to 2.2-2.3, and then it stays there until 90. I'd say the gauge was busted, but it shows up in the mileage for that tank of gas.
@Toxeia: Oh, it's constant engine speed from 65 through 90? I really don't know the Maxima, is there an Overdrive?
Does the engine sound the same from 65 to 90? You should be able to tell the difference just by its sound.
@Toxeia: That's what I meant, thanks for the correction. You cannot go two different speeds at the same RPM without more or less engine load. It cannot be done. There are fixed ratios in every modern car transmission and the laws of physics dictate that to go 65 mph with one engine speed you can't go another engine speed with the same RPM unless the loading on the engine is different. Changing the load on the engine, more or less load, impacts fuel economy. You can't get the same economy at two different speeds at the same RPM, the engine load is being changed and you are burning more or less fuel. I can cruise at 2k in my truck going 70, but if I load it full of crap and pull a trailer I can also go 70 with the engine turning 2k, BUT the engine load is higher because I'm moving more weight and my economy tanks. Unless your gauge is broken, or you have nothing in your car except what it needs to run you aren't going to get better mielage at a higher speed. I'm guessing your gauge is busted and calculating off of one tank isn't enough to tell you definitively that your mileage is better. That's why I am so harsh on the Mythbusters on here. I've said many times before they don't do real science because the number of variables, especially in their fuel economy tests, are so varied and so important that their testing is null and void because they won't factor them out sufficiently.
@Greg818: Mass does have an effect because no road is perfectly level and you're always going to be changing the engine load. Modern cars are able to lean out their mixture for cruise but even still turning more RPM on a fixed ratio transmission is going to cause fuel consumption to go up. Drag squares with speed, I think that's the correct ratio I may be wrong, so even on a slippery car you're increasing drag every time to increase your speed and so your car engine is doing more work. Turning an engine faster will burn more fuel over time and testing with one or two tanks of fuel isn't going to give you a definitive figure.
Toxiea fixed my statement in his post, I meant that in the same gear you can't physically turn the same RPM at 65 that you are turning at 90. It simply isn't possible because gear ratios are fixed and you can't turn an engine at two different RPM speeds and get the exact same wheel speed. Nissan has put out a few CVT cars but his year model wasn't one of them. Unless he's tucking his mirrors I don't see how it's possible to vary the speed 30 miles an hour faster an get better economy. His car isn't all that slippery and the increased drag on the car will cause fuel consumption to go down. Even slippery cars like the Vette and others will get worse economy with speed simply because of aerodynamic drag. My point about weight was based on your typical road being undulating. My truck can get 18 MPG on a good day. Same road, same traffic, different weight it will have to work harder even on the smallest of inclines and that burns more fuel.
@Greg818: Yeah, there's an overdrive. I always figured it was just an extra gear or something.
@Toxeia: To put it crudely, overdrive is a two ratio gearbox in series with the actual gearbox. So, it is possible that, while in the same gear (gearbox), if it's an auto overdrive, you can get the same engine speed, that's why I was asking. But cars (as opposed to trucks), will by default always be in overdrive. Now that I think about it, it's the same on trucks as you have the tow/haul mode... But still, 2.2k at 90MPH seams like an unusually long ratio for such a car.
@HKZ: Man, you're mixing up plenty of things here, I don't know if it's in your head, or when your write it down though. Drag is a constant (drag coefficient), thus no matter the speed, it will be the same. But you've got right, simply put, the drag induced force is proportional to the square of the speed.
Also, I didn't say mass had no effect, but much less than drag. At highway speed, constant speed, drag will be more significant, that's one of the reasons why trucks are still the same weight yet more fuel efficient. Well, work on the aerodynamics and engine too (and drive train and all...). Plus when you hitch a trailer you change drag, rolling friction, and weight by a quite a huge margin, so it's really no a good example to take.
And I'm sorry to be a nitpicker again, but I have to disagree about mixture. Cars don't lean out their mixture per se, it's still constricted to the same values because of exhaust temperature (EGT vs mixture forms a bit of a McDonald's M with the dangling part being 14.7), compression ratio, emission restrictions... so in the end they stick to the V part of the M, which doesn't make a lot of difference (though cars sold in the US, that means modern ones, as in emission regulated, car actually go way more on the rich side when floored, compared to what is allowed in Europe).
Anyway, don't have much more time, but drag, at highway speeds, has a lot of influence on fuel economy, more than anything else, that's why the Mercedes E class, can turn in fuel economies better than lighter, less powerful cars, that's why they work so hard on hybrids to lower the drag (and rolling friction), and not so much on the weight (they still do, but put less effort there).
Edit: I do fully agree on myth buster, if they were anywhere near science, well, first they wouldn't even do that show, because they'd already know what to expect, and they wouldn't have so many unexpected results (first that comes to mind for me is the bowling ball incident)
2006 Jeep Wrangler, 4.0L, auto, 32,000 miles
I made an Excel spreadsheet for keeping track of my mileage and costs. I log any maintenance and modifications and it breaks everything down into per month, per year and grand totals. I scan all the receipts into PDF files as well.
I also use an app called aCar. I enter in the maintenance and modification records here too, but it's primarily for keeping track of my fuel use. It generates all kinds of cool stats, graphs and charts if you're into that sort of thing.
Fun facts:
@Bane: Nice ride! Do you do a "lot" of off road? Do you know the final drive? Cause that's a neat milage, can only dream about it with the Raptor (just a little 12MPG average in the last 9 months, but quite a bit and sand trails)
OK, I also keep all of my fuel receipts, so here are some numbers:
From June 26 to August 5 (2012):