What's your fuel economy to weight ratio?
 

JanGeo just posted an inspired question in response to my 100+ segment:

He asked how many MPG per pound it worked out to.

What a great question. Speed performance enthusiasts love to talk power to weight ratios. So why wouldn't efficiency performance enthusiasts compare MPG to weight ratios? (Aside from the fact that one ratio is a set of fixed numbers and the second ratio isn't, necessarily...)

FYI, my 3 month (3 tank) average is currently 59.3 (US). The car weighs 1830 lbs.

Edit: instead of the original suggestion of mpg/weight we're going with this formula...

vehicle weight (lbs) * MPG / 1000

... to get "pound miles per gallon (/1000)"

1800# * 59.3 / 1000 = 108.519 for the Blackfly

What's yours?

My 3 month avgerage 34.4. Car weighs 3950.

That's .0087 I need to carry a lot of decimals.

:)

I added a digit to my ratio. I suspect 4 decimal places will work for most.

would the measure of efficiency be the mpg multiplied by the weight then divided by some constant? the efficiency to weight ratio doesnt really say anything...

see:
with driver:
40/2300 = .01739
without:
40/2130 = .01878

and are we doing this with or without the driver?

anyway i think we should divide by 1000. its funny cus now you cant call it a ratio. product?? haha the efficiency to weight product.

with driver:
40*2300/1000 = 92
without:
40*2130/1000 = 85.2

My average is 32.2 My cars weight is 2350

That is .0137

Mine's about 2500 lbs, and my last 5 tanks average 39.8.

However, I think it should be multiplied, not divided. A semi getting 100 mpg should be more impressive than a metro, but the ratio would be lower.

The result would be in pound-miles per gallon.

did anyone read my post??? what the piss?

Actually power to weight is done differently. It's the biggest number divided by the smaller number. My car is 2990 lbs and my hp is 150. So that equals to 19.93

But I like your method of MPG because your number increases as the MPG.
I'll play along.

BEFORE starting mpg gig:
24mpg and 2990 lb car = .0080

AFTER starting mpg gig:
29.92mpg and 2965 lb car = .0100

So mine is

56.5/2200=0.0257.

But the number gets higher if your weight is lower. From reading JanGeo's original comment, he was trying to show that you should get more credit for having a heavier car. My immediate thoughjt would be weight/FE, not the other way around.

So in my case, 2200/56.5= 38.94.

But if I were able to get 56.5 MPG in a 3000 lb car, the number would be 53.10, which would give a higher score to someone who did the same with more weight.

I dunno, just my backwards way of thinking.....

I think Metro's number system is better because it increase with fuel economy. The other option makes the number go down and it's confusing. But, we all know it doesn't matter how much your car weighs, it's the MPG that counts.

You nailed it - tough being right isn't it! I has to be a product because it then becomes an efficency measurement. Now lets throw in frontal area too.

I read it but your theory was too much for my brain at 3am your greatness.

So what you're describing is pound-miles per gallon. It goes up with weight, and it goes up with raw mpg. In other words, it's the average number of miles your car can drag each pound per gallon. :cool:

Raw mpg is still impressive, this is just another statistic. If you can get a heavy vehicle to get a large number, then it says something.

example - light car vs. heavy car:
30 mpg * 1800# / 1000 = 54
30 mpg * 3200# / 1000 = 96

(that 1800# car would have to get over 53 mpg to get to this number - as some of you do!).

The correlation between the utility of a vehicle and it's weight merits a thread of its own. Or maybe you can multiply by the average 'occupant seat-miles' of actual usage. :)

we should definetly figure out some kind of a formula for weight and mpg. Because some of us don't have 3 cylenders, lightweight car, manual transmission, honda engine, small displacement motor. With the formula with can show who made more progress. Of course the thing under our sigs that showed a % hypermiling was accurate too.

That's weight to power. It can be done either way: power to weight ratio - Wikipedia

I don't really mind which formula we use for efficiency and weight, or whether the figure rises or declines relative to efficiency. The interesting information comes from comparing multiple vehicles as long as we're using the same formula.

In lb-miles per gallon, the Fireflea is:

1800# * 59.3 / 1000 = 108.519

JanGeo suggests factoring in frontal area as well, though it would be more accurate if you factored in CdA rather than just A.

finally people are responding :) anyway are we doing this with or without drivers?

also, metro, could you take everyones statistics and put them in the first post of the thread? like to consolidate the information?

adding the frontal area or cd or both could be too much. in the end your just factoring them out. but if a higher number is better then you want to multiply the number we came up with by the product of the frontal area and the cd. the problem is that most of us no longer have the cd that our cars came with from the factory. so maybe just frontal area and well will then have our generalized number for the efficiency of the drivetrain and aerodynamics. in the end these are the things that all of us tend to modify anyway right?

i think it would be cool to see the significance of the statistics. the efficiency-weight product and efficiency-weight-size product next to each other for each car.

Yes I agree! Some of us have SUVs and full size V-8 cars and trucks. I think we need our own section on the Forum for Full Size, Trucks, SUVs, and Cars with V-8s!!!

Let's do it without drivers.

I'll compile a summary in the top post in a day or so when more people have had time to respond.

Sorry for being dense, but I can't wrap my brain around that lb-mile per gallon number. It doesn't make any sense to me at all. I can understand people wanting more credit based on the type of vehicle they drive, but wouldn't a point system make more sense than a single screwball measurement?

thats worth pondering. i have a feeling its a good suggestion for the future as this site grows and by that i mean as the cost of gas goes up but the value of the big v8s wont return enough to justify selling it in place for the gas sipper.

i bet there are a lot of things that can be done to the bigger cars that havent been thought about just because there are not many minds out there that would think to do so.

<--*continues to ponder*

What about a simple point system with a baseline of 50? For every mpg over the EPA average you get an extra point (or lose if under). My Metro would score a 47 right now.

Anyone with a severely modded vehicle should take the average of the EPA averages for every vehicle they've borrowed major parts from (chassis/body, motor, transmission) - they should end up with a very high score then.

This way even an F350 getting higher than the EPA average could beat any other vehicle.

Just a suggestion. I know it's not hard, cool numbers like mpg/pound (wouldn't mpg/tonne produce a more sensible number?), but at least it would keep everyone in the running vehicle type be damned.

I like where this idea is going. if we are able to decide on a formula that we all agree on then I can add this to the garage. When you pull up a vehicle you'll see year, make, model, 90-day mpg, curb weight, and this ratio. We can even do a top-ten.

Not fair! The heavy vehicles are only going to improve a few MPG. Light weight one will show a bigger improvement for the same mods. It needs to be a percentage over or under the EPA.

But isn't that the point? A point scale would show just how far you are willing to go to get the mileage OR the maximum that the vehicle can achieve.

Performance is the same way. You can add a lot less to a lighter vehicle to make it rip the hair off of a heavier one.

Any point system will eventually favor the lighter/smaller/modified vehicle simply because the large/heavy/powerful one is already running at a deficit.

Did we not already have this with the last gas log that showed where you were in relation to EPA values. What wrong with that?:D

Yeah, we did, but everybody seems to asking for a ratings/comparison based on MetroMPG's mpg:weight ratio which won't work since it's only one number in a huge field of numbers. It's like comparing a Vette and a Viper based on HP ratings alone.

I thought a base of 50 puts everyone on level ground and then you just add/subtract from there to see how your vehicle/driving compares. A point system is a great idea I think. I think percentages can be misleading at times since you don't necessarily immediately know what the percentage stands for.

i think its important to have both the efficiency-weight product and the over epa percentage. because some cars are a lot easier to squeeze efficiency out of than others. there is no need to replace one with another. also weight is usually a good indicator of how big a vehicle is. you could do frontal area but that really only covers so much and its a more difficult statistic to get your hands on. i am totally unaware of my cars frontal area. but i know its weight.

also i think these formulas should be kept simple. any more an we will have to start taking derivative of the torque curve at the mean rpm and dividing by the blablablabla nobody cares.

2 simple formulas:

efficiency-weight product
= lbs * mpg /1000
this shows a general idea of the overall designed efficiency for the car in its class as compared to others, both the dealers design and your modifications

hypermiler percentage
= 1 - (epa mpg / actual mpg)
this shows a general idea of the improvements youve made over the factory design and average driving style.

also there should be some way of taking two averages. this was my tick with the old gaslog. my ending average mpg was my average since december, back when it was 33-34mpg. the last 10 tanks were over 38mpg and the last 3 over 40mpg. i think the average of the last 5 tanks should be the average that is displayed. that will also cause a much more dynamic top 10

sorry for another novel status post but i dont know how i could condense it. trust me its worth reading:)

But could what does the resulting number mean? I don't understand it at all...:confused:

I like the lb*mpg/1000

the higher the number the better

My number comes to 128.93(2392x55.43/1000) with las weekend's trip.

Which is why people with heavier vehicles seem to be favoring it, but the number seems to be completely meaningless and the term pound-miles per gallon makes it even more meaningless. At least mpg per pound made sense though it's hardly an absolute and doesn't tell you much vehicle to vehicle.

mpg/ton would give a larger number overall. At 44 mpg my car would be 48.7 mpg/ton.

I just don't like numbers that don't have any particular meaning and unless somebody can give me a concise, rational explanation for pound-miles per gallon it I'll vote against it.

Pound-miles per gallon: 80

Metro, if you don't have the time I'll make a table of everyone's stats in your original post, lemme know.

Sorry, I know I'm probably bugging everyone by now, but I had to figure out some meaning to this pound-miles per gallon thing...which I can only do if I have some basis to go by.

Using the EPA average, my Metro should be 84.0255 (1807*46.5/1000). However, it actually is 1807*43.041 (average of last 3 tanks) /1000 = 77.7751.

This makes my car 7% under the EPA lb-mpg...which is interesting, because I come up with the EXACT SAME percentage if I just use the mpg numbers:

1 - 43.041/46.5 = 7.439%
1 - 77.7751/84.0255 = 7.439%

Can somebody please show me the point in lb-mpg now??? Yes, I'm a pain in the gassavers...

Vehicle weight is going to be a greater factor with people who do a lot of city driving or a lot of steep hill climbing. I agree that if we are going to come up with some kind of equation to give everyone a level playing field, then cdA is going to have to be factored into the mix.

The point of lb-mpg is to factor in vehicle weight. *shrug* though, no baseball fans to figure out good stats for us to use.

But I just proved that on a percentage basis it doesn't factor in anything - it's just a bigger, prettier number that's completely meaningless.

If people want a level playing field then we have to come up with a ratings system that we can all agree on. What about something like this:

Fuel Economy Point Chart

Base points (stock vehicle): 50
Hybrid: -5
Featherweight (under 1 ton): -5
Middleweight (1 to 1.5 tons): 0
Heavyweight (1.5 to 2.5 tons): +5
Ultra-Heavyweight (over 2.5 tons): +10
Manual Trans: 0
Auto Trans: +5
Bone stock meet or exceed EPA (driving style points): +10
Mods: +1 for each mpg increase

I know, that's why I said we needed good stats...but nevertheless, it does factor in vehicle weight.

How about something like:

(cdA * MPG) * ( 1 + (Weight / 2000)) = X

So my d15z1 CRX would be:

(5.71 * 62) * 1.75 = 619.5

Let's see, that's about 3000 miles and 6 months.