Spreadsheet I made showing diminishing returns on MPG

Here is a spreadsheet that I made to show the diminishing returns of MPG, as well as to have an easy tool to compare different cars cost as far as fuel consumption goes. Google docs is a little on the clunky side, so I did not kill myself formatting it--sorry.

The first tab (on the bottom) is open for anybody to edit it. Please don't play with any of the cells except the ones in blue. These are for you guys to play around with, you can edit MPG, price of gas, as well as miles driven in a year for various comparisons.

Click on the second tab for the output.

You can change the "current and new" MPG figures--for instance, if you wanted to see what the change was from a Ramcharger to an F-150, a Ramcharger to a Prius, and a Ramcharger to a (uh... what gets 1001 mpg?), you can enter in 8 and 15, 8 and 40, and 8 and 1001. It only goes to 1007. You can do 3 comparisons at a time per gas price/mileage.

You'll notice on the output tab that there are a also a bunch of comparisons that cannot be changed--these are ones that a lot of folks probably wonder about, showing 5 mpg increments and how much it saves you from 15 to 30, 20 to 35, and 30 to 45. If you scroll down you will see it for the second gas price as well.

Enjoy!

https://docs.google.com/spreadsheet/ccc?key=0Am2g02d7X8CndG0wenBPOW9oSUlfc1k5czNHeWc3Znc&usp=sharing

A cool thing that I like to see with it is how there is the same difference from 20 to 30 as there is from 30 to 60. From 60, there is a smaller difference to 1007, than to 30. 1007 is the highest this spreadsheet goes.

I did a similar analysis a few years ago and came to the same conclusion. There's a huge reduction in cost when you go from say 12MPG to 25MPG, but the benefits are much less impressive from 25MPG to 35MPG. Especially when the more efficient car requires premium gasoline. I drive about 20k a year, and the only thing that made much sense from a pure financial perspective was a Prius, and that was only if you ignore the buy-in cost over my current DD.

I'm patiently waiting for an electric car that's reasonably priced with a 125 mile range so I can make my 60 mile round-trip commute in the winter...

dj06482 wrote: I'm patiently waiting for an electric car that's reasonably priced with a 125 mile range so I can make my 60 mile round-trip commute in the winter...

Yep, that's one of the reasons I went with a Nissan Leaf. My commute is 50 miles round trip, and with a 75+ mile range, I'm comfortably within it's abilities.

I like the spreadsheet!

dj06482 wrote: I did a similar analysis a few years ago and came to the same conclusion. There's a huge reduction in cost when you go from say 12MPG to 25MPG, but the benefits are much less impressive from 25MPG to 35MPG. Especially when the more efficient car requires premium gasoline.

Do a test. Quite a few cars exist where 92 octane gets better fuel economy than 87, so there will be a point where it crosses over and it's cheaper to run on premium.

At 30c/gallon difference, the break-even point for my Golf was somewhere around $2-$2.50. At the time I had it, fuel was $4.50 for 92.

Golf drank the good stuff, it did. PO was amazed that I was getting 40+mpg when he only ever got mid 30s. That was the difference.

$4.50 at 42mpg is about 9.3c/mile. $4.20 at 35mpg is about 12c/mile.

Sadly, the low-compression, non-knock sensing VW I replaced it with does not care for octane, and gets the same crappy fuel economy no matter what I feed it. So I went the other way and tried using cetane booster in 87 octane, and it helped economy a couple MPG but not enough to pay for the cetane enhancer.

Klayfish wrote: Yep, that's one of the reasons I went with a Nissan Leaf. My commute is 50 miles round trip, and with a 75+ mile range, I'm comfortably within it's abilities.

The Nissan Leaf is VERY interesting to me. With a 15 mile total daily commute, plus additional errands, I would always be in range of the vehicle. (I have a second car for vacation, hauling, longer trips)

According to the Nissan site, I can save $780 in gas every year. My payment for the car could be as low as $330. So I could make money buying a Leaf.

My wife could save $1,200 in gas in her 45 mile commute.

pinchvalve wrote:

Klayfish wrote: Yep, that's one of the reasons I went with a Nissan Leaf. My commute is 50 miles round trip, and with a 75+ mile range, I'm comfortably within it's abilities.

The Nissan Leaf is VERY interesting to me. With a 15 mile total daily commute, plus additional errands, I would always be in range of the vehicle. (I have a second car for vacation, hauling, longer trips) According to the Nissan site, I can save $780 in gas every year. My payment for the car could be as low as $330. So I could make money buying a Leaf. My wife could save $1,200 in gas in her 45 mile commute.

Same here, although it would be $1000 a year in gas, and I typically avg 26-27 per tank in my car on premium. Not sure I would like driving it though.

A two year lease on a base model is very intriguing as it would allow even more money every month to go into savings to get prepared for an eventual truck/trailer when the Miata goes track only.

pinchvalve wrote: The Nissan Leaf is VERY interesting to me. With a 15 mile total daily commute, plus additional errands, I would always be in range of the vehicle. (I have a second car for vacation, hauling, longer trips) According to the Nissan site, I can save $780 in gas every year. My payment for the car could be as low as $330. So I could make money buying a Leaf. My wife could save $1,200 in gas in her 45 mile commute.

I put more details in my Leaf thread last week, but you should be able to get one for less than $330/month. I put $2k down and pay $249/month for a loaded model. A base is around $159-$169/month if you bargain hard. With $0 down, it would probably be $240ish/month. 15 mile commute would be a snap. Here was my math. My lease is 15k miles/year. Between the cars that it is "replacing", they averaged 25mpg. That's 600 gallons of gas. At $3.59/gallon average, that's $2154/yr. I plan to use every one of those 15k miles per year.

That said, they're not for everyone. I like the fuel calculations mtn has. I was going through all the numbers a lot before I bought...i.e. how much would I save if I got 40mpg vs. 25? What if I could squeeze it to 42? Obviously, the difference between 40 and 42 is minimal, so that became a non-factor, it was just the big chunks.

pinchvalve wrote:

Klayfish wrote: Yep, that's one of the reasons I went with a Nissan Leaf. My commute is 50 miles round trip, and with a 75+ mile range, I'm comfortably within it's abilities.

The Nissan Leaf is VERY interesting to me. With a 15 mile total daily commute, plus additional errands, I would always be in range of the vehicle. (I have a second car for vacation, hauling, longer trips) According to the Nissan site, I can save $780 in gas every year. My payment for the car could be as low as $330. So I could make money buying a Leaf. My wife could save $1,200 in gas in her 45 mile commute.

This is one of the things that justified the Volt for me. My day to day driving uses no gas, so I save $200 a month over the car I traded in right off the bat. Funny thing is, it damn near paid for itself over the cost of driving the previous paid off car just in fuel costs alone.

I was talking to a lady that has a paid off 12 year old Ford Explorer that she puts in $100 a week in gas. A car like the Leaf or Volt would pay for itself starting the first month due to the gas savings alone.

Knurled wrote:

dj06482 wrote: I did a similar analysis a few years ago and came to the same conclusion. There's a huge reduction in cost when you go from say 12MPG to 25MPG, but the benefits are much less impressive from 25MPG to 35MPG. Especially when the more efficient car requires premium gasoline.

Do a test. Quite a few cars exist where 92 octane gets better fuel economy than 87, so there will be a point where it crosses over and it's *cheaper* to run on premium.

Two gas price fields on that spreadsheet

pinchvalve wrote: According to the Nissan site, I can save $780 in gas every year. My payment for the car could be as low as $330. So I could make money buying a Leaf.

Huh? How would you make money? I assume your current vehicle is paid off, so instead of $800 in gas, you'd be paying $4000 in payments.

In reply to mtn:

He makes money when he compares the annual fuel savings to the monthly payments.

I can't look at your spreadsheet right now- but I look forward to it later.

Anyone want to run a comparison between a Leaf and a Hyundai Elantra? 38 mpg, $19000 purchase price, runs on regular fuel.

I can't access the spreadsheet while at work, but when I get home I will update the sheet to add an electric car option--I'll make it 1,000,000 MPG to approximate ∞.

I'll also add in the return fields on the front page, but since that sheet is not locked, anyone can mess with it and it might get deleted. Actually, anyone can try that now--you should be able to copy from the protected sheet.

Anyone interested in the original excel document, PM me and I'll email it to you. The formatting is much better, and the MPG goes up to 11. No, wait--10,000.

Chris_V wrote: This is one of the things that justified the Volt for me. My day to day driving uses no gas, so I save $200 a month over the car I traded in right off the bat. Funny thing is, it damn near paid for itself over the cost of driving the previous paid off car just in fuel costs alone. I was talking to a lady that has a paid off 12 year old Ford Explorer that she puts in $100 a week in gas. A car like the Leaf or Volt would pay for itself starting the first month due to the gas savings alone.

Yep, stepping out of something that gets <20mpg, like an Exploder, and going into an EV will pay completely for itself if driven a decent amount of miles. One nice thing about the Volt is that when your battery runs out, you (OK...the car) fire up the gas engine and go. When the Leaf runs out, I fire up my Nike's and start walkin'.

SVreX, To do comparisons, you'd need to include miles driven per year, how long you'd own the Elantra, etc... Most people lease the Leaf, so you walk away with no equity vs. buying a car like an Elantra. Also factor in maintenance. Leaf requires basically none. Elantra probably would be very little too, but still something (oil changes, etc...).

Chris_V wrote: I was talking to a lady that has a paid off 12 year old Ford Explorer that she puts in $100 a week in gas. A car like the Leaf or Volt would pay for itself starting the first month due to the gas savings alone.

the only problem is that loans to get such vehicles are still super tight.

most people wouldn't be able to get enough credit at a good rate to bother with it...

also the whole 'not for sale in all markets' thing...

This is part of what I use to determine the relative cost of a different vehicle. Use net cost and estimate resale to determine actual savings over 5 years. Note: the lower part is a separate but self explanitory function.

It's a little rough, and metric. It's worth about what you paid for it. ;)

https://docs.google.com/spreadsheet/ccc?key=0AifxTObEEQISdEMwdGZYaHZhci1NR3c2WHhvUFlRR3c&usp=sharing&authkey=CL32nZ0K

Knurled wrote:

dj06482 wrote: I did a similar analysis a few years ago and came to the same conclusion. There's a huge reduction in cost when you go from say 12MPG to 25MPG, but the benefits are much less impressive from 25MPG to 35MPG. Especially when the more efficient car requires premium gasoline.

Do a test. Quite a few cars exist where 92 octane gets better fuel economy than 87, so there will be a point where it crosses over and it's *cheaper* to run on premium. At 30c/gallon difference, the break-even point for my Golf was somewhere around $2-$2.50. At the time I had it, fuel was $4.50 for 92. Golf drank the good stuff, it did. PO was amazed that I was getting 40+mpg when he only ever got mid 30s. That was the difference. $4.50 at 42mpg is about 9.3c/mile. $4.20 at 35mpg is about 12c/mile. Sadly, the low-compression, non-knock sensing VW I replaced it with does not care for octane, and gets the same crappy fuel economy no matter what I feed it. So I went the other way and tried using cetane booster in 87 octane, and it helped economy a couple MPG but not enough to pay for the cetane enhancer.

How does a vehicle get better gas mileage with higher octane? Higher octane has a lower power density and thus makes less power per gallon.

Higher octane should DECREASE your mileage.

The only factor(s) I am ignoring is ignition timing (if we are comparing THE SAME vehicle). If the vehicle can increase its power by allowing more timing due to the increased knock "safe zone", then it MAY be able to get better MPG. If the vehicle already has max timing with the lower octane, you CAN NOT get better MPG from higher octane. (assuming the same driving style)

Rob R.

P.S. I realize you mention this briefly in your post. I was just clarifying.

I did this when shopping for the Sonata. The offset of the $250ish in gas every month I’m suddenly not buying makes the car payment a lot easier to swallow. Still hurts to write that check, but whatever. Sadly, I don’t imagine I’ll get that big a jump again, unless 8-10 years from now electric cars are more prevalent (could be) or something else has changed, like a societal move to mass telecommuting vs. centralized offices in cities.

I did the same thing, though- Excel sheet for every car I was looking at, including estimates for the “beater with a heater” option(s). Plugged in the mileage of the old SUV, whacked a few MPG off the highway mileage figures for the new cars, and did a big ol’ analysis. At the end, the newer car was the move for us, if only because I’ve realized over the years that I don’t really care to be all that grassroots on the daily drivers/ appliance cars.

In reply to wvumtnbkr:

I get where you're both coming from, I've noticed on some vehicles(sho's and my old ion redline) that recommend premium(rated at the cali piss they call 91 octane), will return 1-3mpg better on 93 octane and about a 1-3 drop running 89, and 3-5 drop running 87.....

Cars that just called for unleaded only actually got a bit worse in my experience.

In reply to wvumtnbkr:

you pretty much explained the reasons in your post. on higher compression engines the ECU will have to pull timing and sometimes also add fuel when running lower octane fuel. the timing advance being tapped out on 87 octane seems to be more of a thing of the past, seeing as we now have standard on most cars variable valve timing with a range of 50+ degrees.

things like direct injection also help, by allowing higher static compression ratios to be suitable for 87 octane, they also open up the potential for better efficiency with higher octane fuel.

Mileage, schmileage. 260 feet per gallon. $16 per gallon.

wvumtnbkr wrote: How does a vehicle get better gas mileage with higher octane? Higher octane has a lower power density and thus makes less power per gallon.

Not necessarily, and often not. That's more of one of those old wive's tales than anything else.

The only factor(s) I am ignoring is ignition timing (if we are comparing THE SAME vehicle). If the vehicle can increase its power by allowing more timing due to the increased knock "safe zone", then it MAY be able to get better MPG. If the vehicle already has max timing with the lower octane, you CAN NOT get better MPG from higher octane. (assuming the same driving style)

Exactly what's going on. Some cars, typically European but some Japanese as well, will run better on premium fuel. They'll run acceptably on the lower octane fuels, so it's not officially required.

P.S. I realize you mention this briefly in your post. I was just clarifying.

No worries there. Incidentally, I've heard from people regarding the Ecoboost F-150 that they get atrocious fuel economy if you tow on 87 octane, but fuel economy gets up over 20mpg again if you use premium. They have fuel strategy in their knock properties.

madmallard wrote:

Chris_V wrote: I was talking to a lady that has a paid off 12 year old Ford Explorer that she puts in $100 a week in gas. A car like the Leaf or Volt would pay for itself starting the first month due to the gas savings alone.

the only problem is that loans to get such vehicles are still super tight. most people wouldn't be able to get enough credit at a good rate to bother with it... also the whole 'not for sale in all markets' thing...

Well, the Volt and Leaf do away with that last concern, as they are available in all markets. At least the Volt is. And the lease deals are pretty easy to get through Ally. Right now it's $269/mo. Not a bad deal, actually, considering you can easily save that much in gas over even a paid off older car.