A fuel economy riddle...with a moral to the story
 

A married couple have 2 vehicles, both powered by gas.

The husband has an antique truck that gets 10 mpg.

The wife has a hyper fuel efficient car of the future that gets 100 mpg.

Both drive the same 12,000 miles per year.

They both need to cut back on fuel costs, so they go to a mechanic to ask him to help them save some fuel.

The husband is told that if he cleans the crud from bird droppings off his roof and inflates his tires to recommended PSi instead of being nearly flat, he will get 11 mpg from his truck.

The wife takes her vehicle to the dealer and the dealer says they have a hyper efficient chrome plated caneuter valve that will double her mileage so she gets 200 MPG!!!

Who will save more money?

Lol, the wife, because she is burning 1031 gallons less a year than her husband ;)

Sorry, for the sake of the story, it's whomever is saving more money compared to their old MPG figures. Sure she is using a fraction of his fuel, but she can't haul stuff around in her econobox like he does.

lol, I'm just messin. I am a little concerned that there's a moral involved with this hypothetical though :)

She could get the job done with a trailer or a rental, but let's suppose he's a lumberjack by trade and he likes to take his work home with him. Or maybe he's just really stubborn.

He'll actually save more gas just by inflating his tires properly than she'd save by replacing all her bodywork with dry carbon fiber, installing movable aerodynamic devices, getting manual control of her electric motors, and developing that $3000 thermoelectric exhaust waste heat recovery system that she would love to use to charge her traction battery.

My boss wastes far more fuel by accidentally bumping his remote starter button (once a week, it seems) than I save by having a car without A/C. Or, for that matter, than I would save with a boat-tail.

Look at the gal/mi data before buying a car. It's a more relevant way that makes this riddle very obvious.

He burns 10 gal per hundred miles. She burns 1. He would go to 9gal/100mi, and she would go to .5gal/100mi.

He would because the mod are free.

This got me thinking about the claim made by Mobil that their Mobil-1 0W-30 could potentially increase mileage by 2% over conventional 5W-30. I was standing in the store thinking, "Hmmmm. 2% isn't very much. But I'm already getting 35 MPG by ecodriving my car. So 2% on top of that is much better than 2% on top of the EPA estimated 21 that my car is rated at." On the surface it sounds like the more fuel efficient your car is, the more this oil could potentially save you. The reality is actually not as bright.

The better your FE, the less money you will save.

not sure you did that right. it isn't at all obvious when fuel is in the denominator so lets flip it.

in your scenario car A(10mpg) gets .1 gpm (gallons/mile)
and car B(20mpg) gets .05 gpm.

so @ 10k miles a year they would use 1000 and 500 gallons respectively.

so 2% of that would be ~20 gallons and 10 gallons respectively "saved per year".

The other "gamey" aspect of this is that the fuel returns seem to taper off as gallons used approaches zero.

If you were to assume we had, say, rations of fuel (it's happened before), where you only get 500 gallons a year and were to look at how many miles you could travel on that allotment with different cars it puts a different spin on things.

@ 500 gallons/year

a .1gpm car could go 5000 miles
a .05gpm car could go 10000 miles
a .025gpm car could go 20000 miles

so in each case we decreased consumption by 50% and doubled the range.

Pickup guy went from 1200 gallons of fuel per year to 1090.91 gallons, saving 109.09 gallons of fuel. Hyper efficient wife went from 120 gallons of fuel to 60 gallons, saving 60 gallons.

Now if she could convince him to drive an efficient car to drive to work and back and keep his pickup truck for cruise nights with the car club guys, the savings could pay for that new paint job he's probably dreaming about.

OP -

This forum, like many others, will NEVER give you a straight answer to a question like this. There are too many points for discussion and fervent outbursts (that others might not even notice) for this thread to have gone any other way.

Just thought you should know that so you don't get frustrated when this keeps happening... LOL.

This is a perfect example of why the gallons per mile metric is better than the miles per gallon. Of course, the math is correct either way you do it, but our mind more easily grasps the actual improvement when we look at the gallons per mile figure...
10 -> 11 mpg = 0.1 -> 0.09 gpm
100 -> 200 mpg = 0.01 -> 0.005 gpm
Answering the question of which gain is bigger is much more intuitive when you use gpm.

Of course not, because it's a loaded "Have you stopped beating your spouse?" question, for which any straight answer you give is wrong. (OK, unless you actually HAVE been beating your spouse :-))

The correct answer, of course, would be for the husband to junk his pickup in favor of one that got halfway decent mpg. Used '80s Toyota 4WDs can be had for $2-3K, and will get over 25 mpg driven in working conditions.

I gotta decimal point wrong....

LOL everyone saw through it all pretty quick.

I suppose the moral is that small MPG increases in a larger car are to be preferred to large mpg increases in the smaller car.

The car manufacturers have it all wrong in how they try to boost their fleet economy. Instead of making the big vehicles get better economy, they take a 1.5L small sedan and add an electric motor and battery pack and make it even more economical. Why not do that with their pickups? Or their minivans?

If a family has 2 vehicles seeing similar miles, but 1 is getting much worse economy, the focus should be to get the 10 mpg truck up 5 mpg rather than to get the 40 mpg car to 50 mpg. Sure, a smaller car gets much better mileage, but you can't haul 4x8 sheets of plywood in the back of the Metro. (well, not easily :P)

lol, I was afraid that was the "moral" :) Really there isn't a comparison though. If you've sucked it up and got a small car more power to ya, if you are stuck with what you have then make the most of it.

Just FYI, I have a $200 4x8 trailer that can, easily, and can still get 45mpg behind my saturn. Seen metros & diesel rabbits with tow hitches too. If I kept this setup vs a larger vehicle that gets 22.5 mpg, I would recoup that $200 in 3 months.

I think your answer deserves a prize, because it accurately addressed the salient point of the way in which the riddle was framed. The implication was one of who would save the most money after seeking (and presumably acting upon) the professional advice given. One proposal involved spending money (on a technical gizmo), the other in spending nothing. If neither took any action at all, the status quo would remain the same.

He saves by not spending anything, nor losing anything. His potential return is risk-free and his attaining anything more than zero is a pure benefit. She hopes to increase her benefit, but only after pinning her hopes upon and recouping the capital outlay spent on the (presumably not cheap) recommended whiz-bang, canoodle valve.

It's a case of 'money remaining in your pocket' while losing nothing yet possibly earning potential rewards vs. incurring a debt with hopes of attaining 'pie in the sky'. ;)

My truck has already made up the difference in fuel costs between it and my previous vehicle, a consistent 28-29 MPG Dodge Caravan.

Sure, I used the Caravan to haul things as well (check out my albums), but the truck can haul SO MUCH more. Like half a cord of wood. TWO lawn tractors (and a trailer with 5 more on it). I can haul motorcycles without having to lower/remove the handlebars or other parts... and so on.

I went from 28-29MPG down to something like 17 (hard to keep accurate track because I'm going tank to tank... I only drive it when I need to.)

Oh, and my insurance went down $20 a month, as well. Guess that makes up for the fuel costs, a little.

I do have a Diesel Golf, that as soon as I get it on the road, will get a trailer hitch put on it, and stiffer suspension. Why? Cuz I'd be willing to bet that Diesel Golf can handle a 1,000 lb tow load just like my truck can... except it can get 40+ MPG of nearly free fuel doing it. :) I only with it was a turbo... :(

Antique truck with 10mpg and high fuel mileage car? Why don't you just put my name in the riddle? (See sig) :p

this is simple.

the conobox drifts to the wind and 22 guage tinfoil aero mods...
in todays dollars the 16guage fendered truck is 20 econoboxes...

he could haul the econobox.

if an antique vehicles value increases by just 1000 a year, it is another gain on the crap box risking life and limb with tiny wheels and tires....

the truck is not only saving money, it is gaining.

for every 1000 pound payload, it has to be proportianetly applied to the fuel mileage.

To drift off the subject.. I did not want to give my sube up for ayhting (I got the little 1781cc wagon).. I spotted two fairmont wagons with the 302 v8 installed, 5 speed, and welded...
for 10-20mpg less, I could have a car I could go fast in..and still be a wagon that can haul a bit more (not hat I have any complaints, the little sube is the biggest little car ever).. but you may get my point. Thinking larger may have larger bills, but it may return alot more than expected...no short timer eocnomy about it.
If one thinks their little hypermiler is normal... the disease is winning, like a bad cult.
no riddles about it. What exactly is getting saved? some drops in the bucket, and a scarier ride.

lol, assuming the bird poop encrusted 10mpg truck is increasing in value by $1000 a year, sure.

LOL I love the debate this has stirred up.

And the way I framed the story had more loaded statements than I intended to be sure.

olesube also pointed out something I hadn't considered, which is the relative safety of being in a slightly heftier vehicle.

And having a $200 trailer and trailer hitch on the econobox is a heckuva lot better than having a pickup.

Good points from all. This is why I enjoy being on here, there's plenty of intelligent conversation to be had.

[QUOTE=bgd73;174633if an antique vehicles value increases by just 1000 a year, it is another gain on the crap box risking life and limb with tiny wheels and tires...[/QUOTE]

Yeah, like my neighbors' granddaughter, who listened to her family, traded in the cute little "econobox" her dad bought her for graduation for a big safe pickup - and in a few months rolled it, killing her and her boyfriend.

Detroit's "big = safe" scam beats anything pulled off by Bernie Madoff or Goldman & Sachs.

No one said anything about it being trashy, good sir. And yes, antique cars gain value over time. Even the uglyones with the new "patina" trend.
:thumbup:

I didn't make up the bird poop part :)

Yet the people who buy antique cars don't drive them much, maybe to an occasional "cruise" or similar event. A lot of the more valuable ones get trailered from show to show. Very few get used as daily drivers.

I recently sold a '77 Ford rust-bucket truck for $1500 because it would pass inspection, and could haul "stuff". (No details on what it was hauling, but the guy that bought it wasn't too heavy...)

Not a week later, I sold a '84 F150 to the guy's "cousin" (around here, that doesn't mean they're related) for... you guessed it... $1500. Also rusty, also passed inspection, and also could haul "stuff". Both trucks had the same engine installed, 300ci 6 cylinder, same 4 speed transmission in both, and probably the same axle ratios. Both 4x4.

A truck's a truck when it's being used for a truck. It doesn't become an "antique" until some jerk (lightly intended) buys it that doesn't ever plan on making it do anything but use fuel and sit.

Value is relative to the people who might want to buy it. To anyone around here, who's actually looking for a truck, it might be worth ~$1500. If they're looking for a trailer queen POS, more than likely they're not trying to pay more than junk price. Doesn't matter what KBB or NADA say, their values aren't EVER accurate except to the people that use them.