Increasing MS3 fuel efficiency.

[happy and angry]

We are both overweight and tend to carry 100 or so pounds of extra stuff (mostly wife's work stuff, laptop, etc) around with us. I am not convinced a little extra weight makes much of a difference in a 3k+ lb car with this much HP/Tq.

I'm going to make up pretend numbers here to make a point. I'm going to be general with the numbers and keep things simple.

Let's say you have 310 pounds of stuff in the car. You and some gear. You have just added 10% more weight to the vehicle. That is 10% more weight to pull, and as a result about 10% more work to be done to keep it moving at a given speed, 10% more effort needed to accelerate up to speed, etc. That's going to burn a lot more fuel. About 7% more, actually.

http://www.fueleconomy.gov/feg/lightweight.shtml

For every 10 % of weight eliminated from a vehicle's total weight fuel economy improves by seven percent.

So let's add another 310 pounds to the car. Someone else and some gear. That's another 7% increase in fuel burned. Just over 600 pounds and you just killed your fuel economy by a good 14%, which is about 1.4 MPG for every 10 MPG your car gets. That's about 3.5 MPG for our car if you average 25 MPG.

Weight is one of the biggest problems when it comes to fuel economy and performance. Power doesn't matter. Torque doesn't matter. More weight, more work, more fuel burned.

 

[builthatch]

Weight is one of the biggest problems when it comes to fuel economy and performance. Power doesn't matter. Torque doesn't matter. More weight, more work, more fuel burned.

it's exponentially less meaningful during sustained cruise vs. acceleration conditions. physics, of course.

if you plan on driving primarily on highways with cruise control on at 72 mph, you can rest assured adding weight won't matter nearly as much as the person who is commuting through city traffic and going on and off arterial roads.

i am surprised these threads keep popping up because i thought the idea was simple, but evidently it's not. if you drive lightly with no aggression (vacuum conditions), and carry static speed settings for long spans, you will have the best mileage. i've seen calculated mileage approaching 30mpg when doing this. the more you alter those conditions, you use more fuel more often and your mileage goes down to the averages we all already know from our turbocharged small displacement sports cars.

 

[Uze DaFarce]

Power doesn't matter. Torque doesn't matter. More weight, more work, more fuel burned.

It certainly does matter, one extra person getting on a bus makes less of a difference in fuel economy than one extra person getting on a go-cart.

7% regardless of the vehicle? No way that is scientific, even based off an average. I would really like to see the study with the data to back that up, I am fairly certain it's an extremely limited dataset with tons of questionable assumptions.

I agree with you in theory, that weight does impact performance and MPG, but I just haven't seen much of a difference IRL. In cars at least. There is a hugely noticible difference in boats, but at least 90% of that is due to planing, resistance, and drag.

 

[Uze DaFarce]

I realize % of weight makes my example look dumb. I am trying to come up with a better one.

EDIT:
I thought of an example:
http://www.hyundaiusa.com/vehicle/santafe/specs/specs.aspx

Look at the differences engine/curb weight/hp in GLS/SE/Limited Hyundai Santa Fe, now look at the differences in the MPG.

I realize this isn't anywhere near a scientific example either, but I hold that it's fairly typical of RL experiences.

 

[happy and angry]

I realize % of weight makes my example look dumb.

...

I realize this isn't anywhere near a scientific example either, but I hold that it's fairly typical of RL experiences.

Power of the motor really doesn't matter that much from the perspective of efficiency. A more powerful motor doesn't respond more favorably to added weight in terms of fuel economy, you just won't feel the vehicle bog down with weight as a result.

Again, the more the vehicle weighs the more energy that is needed to produce the same amount of work. This is obvious, right? It's harder for you to lift 200 lbs than it is 100 lbs. Where does the energy come from in a motor to "lift a weight" (move you forward)? Gasoline. It's even a linear relationship, where as weight goes up the energy necessary goes up by a like ratio.

Obviously it is not quite linear in a car. Gearing, torque distribution, and rates of acceleration ensure this. You still need to burn more fuel to move a heavier vehicle, but you can improve engine efficiency with mechanics, or gearing. This is one way a semi-truck manages to pull heavy loads without making enormous sacrifices in fuel economy.

I linked you to a scientific study, and you don't really seem to believe it. It's likely an average, but you can safely use that to estimate the rate at which overall fuel consumption will increase as load on the motor increases. If you're bothered by it because you're overweight and weight is a sensitive subject for you... well... not sure what to say.

The problem is going to be more pronounced during acceleration than at a cruise at a steady speed, but even at a steady cruise you will be burning more fuel to maintain the same speed in your car if it is heavier.

 

[Uze DaFarce]

... Again, the more the vehicle weighs the more energy that is needed to produce the same amount of work. This is obvious, right?

Yes, but what is not obvious is how much impact is observable.

It's harder for you to lift 200 lbs than it is 100 lbs. Where does the energy come from in a motor to "lift a weight" (move you forward)? Gasoline. It's even a linear relationship, where as weight goes up the energy necessary goes up by a like ratio.

The car doesn't have to "lift", it has to move. Underwater lifting or moving weight with a hand-truck (dolly) would be slightly more accurate examples, but still way too simplistic to be at all helpful in this case.

...
I linked you to a scientific study, and you don't really seem to believe it. It's likely an average, but you can safely use that to estimate the rate at which overall fuel consumption will increase as load on the motor increases. If you're bothered by it because you're overweight and weight is a sensitive subject for you... well... not sure what to say.

The parts relevant to this discussion seemed to simply be editorial comments. There is no data whatsoever on that page, cited or otherwise which would give any indication that scientific research was used to determine the 7%. What makes it seem scientific to you? The .gov in the address? The reference to researchers? The fact that there are actual scientific studies about fuel consumption listed on the same site?

LOL, if I was sensitive about my weight, do you honestly think I would post that I am overweight on this forum? I have a low post count, but I have been a fly on the wall here for a long time, I know full well how critical and cruel many posters are here. My post came right after coololddude was making a fat chicks joke... or perhaps you think I am seeking conflict? I guess that would make sense.

...
The problem is going to be more pronounced during acceleration than at a cruise at a steady speed, but even at a steady cruise you will be burning more fuel to maintain the same speed in your car if it is heavier.

Even down hill?

My original point, and the point I have been making all along, is that in my experience a few hundred pounds doesn't make enough of a difference to be noticeable (>~1 MPG - I would consider noticeable). If the 7% is accurate, then I am clearly wrong.

 

[happy and angry]

The study is probably pretty close with the 7% number.

Lifting an object is still moving an object, and it illustrates the same point, but if you don't like how different it is from a car, change it to pushing a wheelbarrow with 200 lb in it versus pushing a wheelbarrow with 400 lb in it. Takes more energy. Any movement requires energy, and in any medium, by any means, more weight means more energy needed to move at a given speed means more fuel burned. I can go into physics equations for this, but I don't think I'll do that.

More examples: airlines. An airline is so conscious of fuel use that they will go to great lengths to maximize fuel economy. They will weigh a plane, calculate how much fuel will be needed to go from point A to point B, and put almost exactly that much fuel in the plane (plus a little extra for safety). The weight of carrying too much extra fuel means fuel efficiency declines and they burn more fuel for a given trip unneccessarily.

Race teams will do the same thing. You can use calculus to figure out how fuel economy will change as fuel weight is burned off. Teams trying to finish a race on a final pit will put in exactly how much fuel they need to finish the race, and sometimes this is less than you'd figure if you assumed a constate rate of fuel consumption. It might even be less than you'd calculate to finish the race if you assumed the rate of fuel consumption was constant. Because fuel economy improves as weight is burned off, a distance that might look like it needs 10 gallons of fuel might only end up needing 9.5.

Check out the manual Golf GTI (3150 lbs) versus the Audi A4 Avant 2.0T (3750 lbs). The GTI gets 22/29 mpg city/highway, the Audi 20/28. Pretty big difference. That's almost 10% city (where fuel economy is most affected by weight, because of the constantly accelerating and slowing down in traffic), and it is slightly less of a difference highway because you are doing much more cruising. And the only difference in those vehicles is weight.

Another link for you:

http://www.fueleconomy.gov/FEG/driveHabits.shtml

Weight matters. Depending on how much extra weight you lug around, it can matter quite a bit. You'll notice it says 1-2% per 100 lbs. Look back at the GTI vs A4 comparison. 600 lb weight difference, just under 10% difference in city fuel economy. That works out to ~1.5% per 100 lbs, well within the 1-2% range given in the link.

Other than proper maintenance and better driving habits, the best way to improve economy is to save weight.

 

[Russm]

Good Day
110 mile commute, 1hr each day in stop and go the rest 65-70 hwy, most always aggressivly seaking to further my position in traffic, combined 29 MPG since I changed to full synt.
MSCAI. MSCBE Shift at 3K

 

[clos561]

Good Day
110 mile commute, 1hr each day in stop and go the rest 65-70 hwy, most always aggressivly seaking to further my position in traffic, combined 29 MPG since I changed to full synt.
MSCAI. MSCBE Shift at 3K

shift under 2k under vac, it will be wonderful

 

[Uze DaFarce]

More examples: airlines

The physics of flying through the air, or across water for that matter, are very different from rolling down the road, as I am sure you are well aware.

Teams trying to finish a race on a final pit will put in exactly how much fuel they need to finish the race, and sometimes this is less than you'd figure if you assumed a constate rate of fuel consumption.

You may want to work with these teams on their calculus, since they end up figuring wrong as often as not.

Check out the manual Golf GTI (3150 lbs) versus the Audi A4 Avant 2.0T (3750 lbs). The GTI gets 22/29 mpg city/highway, the Audi 20/28. Pretty big difference. That's almost 10% city (where fuel economy is most affected by weight, because of the constantly accelerating and slowing down in traffic), and it is slightly less of a difference highway because you are doing much more cruising. And the only difference in those vehicles is weight.

OK, obviously we are not going to be able to get anywhere near a real discussion, now you are only counting weight as the difference in MPG between an AWD car and a FWD car? There are lots of other differences between these cars other than weight, for example aerodynamics, tire sizes/compounds, tank size, wheel base, ground clearance, etc.

http://www.fueleconomy.gov/FEG/driveHabits.shtml
Weight matters. Depending on how much extra weight you lug around, it can matter quite a bit. You'll notice it says 1-2% per 100 lbs. Look back at the GTI vs A4 comparison. 600 lb weight difference, just under 10% difference in city fuel economy. That works out to ~1.5% per 100 lbs, well within the 1-2% range given in the link.

Other than proper maintenance and better driving habits, the best way to improve economy is to save weight.

+/- 50%? Wow, they really nailed those scientific numbers down with their "study". The fact that your example of two vastly different cars matches up with the "study" brings the numbers into question a lot more in my mind.

It's fairly obvious we are going to continue to disagree, and that neither of us has scientific data to back our opinions up. Neither of us have the burden of proof, I was just stating my opinion, I honestly couldn't care less. I keep replying because I love to debate. I much prefer topics where scientific data is availiable than endlessly going back and forth, so let's just say you win the internet, the argument, and life.

 

[tiagotiago]

Guess Mazda will care a bit more about fuel efficiency.


http://blogs.edmunds.com/greencaradvisor/.eec061b

 

[happy and angry]

The physics of flying through the air, or across water for that matter, are very different from rolling down the road, as I am sure you are well aware.

Yes, but the basic kinematic truths remain the same. Why are you ignoring this central point? Did you ever take a class that covered newtonian physics?

You're being obtuse at this point. Inertia and momentum are both functions of mass. As weight increases, inertia increases, and the energy required to overcome that inertia increases a like amount. As I said, this is a basic truth regardless of medium. This is true in a boat, a plane, a car, a helicopter, a train, a ball rolling down the hill, moving your finger, running, walking, climbing a ladder, falling down the stairs... it doesn't matter. If it is being moved it is being or has been accelerated, inertia is being over overcome to do that acceleration, and the energy necessary to do this increases as inertia increases.

The GTI and the A4 were used because they are so close to being the same car in terms of engine and transmission. The additional power loss from the AWD drivetrain is not going to translate directly to an equivelant loss in efficiency loss, and it is a sophistic argument to suggest that it will. The drag coefficients are almost identical, at 0.31 and 0.32, but these only become significant contributors to load on a vehicle at highway speeds. For the purposes of this argument wheel base and track can be ignored. Since rolling resistance from tire width is a function of weight and not simply tire width, your argument here is poorly considered, as while the GTI's tires are 4% narrower, the biggest contributor to this particular issue is the 14% heavier A4 (friction calculations are ALSO a function of mass).

I am tired of you debating on the side of a fundamentally broken view of how physics works. Read this:

http://books.google.ca/books?id=kE9...=X&oi=book_result&resnum=5&ct=result#PPA26,M1

I quote (second paragraph, starting at line 6):

Because the force needed to accelerate a vehicle is purely a function of weight, weight reduction through improved design, acceptance of less space, or materials substitution is a critical factor in fuel economy, especially for the urban part of the cycle.

I could quote further. I won't. I'm sorry my linking you to the U.S. Department of Energy wasn't quite good enough for you, but if it will help, read that book I just linked to in its entirety. Follow the footnotes, it's all sourced to scientific journals and papers. If you wish to continue to disagree with me, you're free to do so, but if you're going to do it with 4 centuries of peer-reviewed Newtonian kinematics, perhaps you need to re-evaluate your position.

 

[chronus377]

How about buying a CAI or SRI, since they do give you a little MPG increase but more importantly they allow you to hear when your turbo is activated. This way you can judge the amount of gas your guzzling through your turbo and avoid it when you want.

Plus they are fun and add more power. Can't go wrong with that.

 

[Uze DaFarce]

Ah, so per that document, bottom of pg 24...
"The EEA analysis does not isolate weight reduction directly associated with other efficiency changes, for example, reduced engine weight due to the downsizing (decrease in engine displacement) made possible by engine efficiency improvement, but instead counts the weight reduction as part of the overall fuel economy induction as part of the overall fuel economy increase associate with the efficiency change. Most weight reduction gains are expected after 1995. The fuel economy gain available from a 10-percent weight reduction is estimated to be 6.6 percent, including the effect of engine downsizing to maintain constant performance. Without downsizing, the fuel economy benefit would be 4.2 percent."

Also, could you explain to me why the much heavier (+762lbs) speed6 gets better city MPG (20) than the speed3 (18)? IMHO, they seem to be as good a comparison as the A4 and GTI.

 

[happy and angry]

All things remaining equal (drive train and motor), a heavier car will get better fuel economy. The line you so lovingly bolded even says this, without downsizing the engine a 10% decrease in weight will improve fuel economy 4.2%. That's about 1 mpg in a car getting 20. So go on a diet, take out your 100 lbs of gear, and you can save money on gas. 'kay?

Here: http://www.google.ca/search?hl=en&q=fuel+economy+weight&btnG=Google+Search&meta=

Tell me how many links you need to go through before you find one that suggests saving weight does not improve fuel economy. Enjoy.

 

[Uze DaFarce]

All things remaining equal (drive train and motor), a heavier car will get better fuel economy. The line you so lovingly bolded even says this, without downsizing the engine a 10% decrease in weight will improve fuel economy 4.2%. That's about 1 mpg in a car getting 20.

Here are a few reasons why I bolded that remark:
1) Are you swapping out your drive train and motor? Doesn't that mean that 6.6% (rounded up to 7) is not a relevant number for our discussion?
2) 4.2% != 7%
3) 10% for less than 1 MPG. I can't reduce it by 10% even by going on a diet and getting the extra 100 lbs of crap out of my car, so less than less than 1 MPG. I started all this by saying it wasn't a noticeable amount; I still hold that less than less than 1 MPG is not a noticeable amount.