calculating gas savings

[kjb516]

I recently reviewed the EPA mpg for every car I’ve ever owned versus the average yearly gasoline price for the entire 22 years I’ve had a license. As I’ve usually been able to achieve nearly the EPA ratings in each car (yes, even in my Prius), I used this number to calculate my average pennies per mile fuel cost since 1982.

To my shock and delight, I realized that I haven’t driven this cheaply since 1986 when I was driving a Chevrolet Chevette (~28 mpg) and gasoline, according to the California Energy Commission web site, was around 87.4 cents per gallon.

[DaveinOlyWA]

Bruceha_2000

i can agree with that. before driving was a hassle and i avoided it a lot without realizing it.

now, i find that i am willing to drive farther and more often.

last weekend for a family birthday, i carted my sister and two kids to my sister-in-laws house. normally, i would have probably driven myself, been late, broke all laws getting there, etc.

now i look forward to it for reasons i am not sure of. the newness of the Prius has worn off (i think) and since my car was a basic model, there isnt nearly as much to play with.

i guess it could be another attempt at showing off the car to someone, but the people in question have seen and ridden in my car several times.

my niece is a 14 year old who like all other 14 year olds constantly needs rides. i now know all her friends and no longer needs directions to nearly anywhere she has to go. because two of her friends live near me, she now calls me first before calling mom and dad, and both are VERY happy about that. (realize both constantly complain about the price of gas while i mention that i dont get gas often enough to remember what i paid for it the last time i filled up)

[Prius Maximus]

I thought I was going to be clever and update my MPG spreadsheet to figure my cost savings over my old car. I came here to brag but you all beat me to it.

Anyway, my old car was a Dodge Neon which got a lifetime average of 27.8 mpg. I am at 50.9 for the Prius lifetime. Since delivery of the Prius in March '04, I figure I have saved $640.

I see there is some confusion over how to figure savings. Here is what I did:

I took the elapsed miles for the current Prius tank fillup and divided it by the Neon lifetime average MPG to get the gallons the Neon would have used. Then I multiplied that answer by the current price per gallon to get the total cost of a fillup for the Neon. That number minus the total cost of the current Prius fillup gives the savings for the tank. A simple summation calculates the total savings. I uploaded a simple spreadsheet into the file library that calculates money saved.

(I have columns in my spreadsheet for total miles, elapsed miles, elapsed gallons, calculated MPG, cost, price per gallon, date, display MPG, and display/calculated mpg difference. Most of these columns have a heading that shows the maximum, minimum and average over all entries.)

[TonyPSchaefer]

Ok, here's my first crack at this. I had a difficult time uploading this file into Geocities. Once I get it finalized, I'll place it on the PriusChat server. I welcome all feedback and input:

http://www.geocities.com/tonypschaefer/Pri...vings_Sheet.htm

[karmavore]

<div class='quotetop'>QUOTE(finman\";p=\"48729)</div>

 
Your results may vary, but I for one see my 'investment' being justified in another 15K miles (roughly $2800 saved in gas).  That should occur within 2 years of purchasing my Prius, well ahead of the 10 year time frame claimed by 'experts'.[/b]

I've been doing the same, tracking my gas savings. Sadly, I don't drive enough to get to "break-even" so quickly. (So I wind up concentrating on the fun-to-drive and fun-to-own and fun-to-think-about factor. Poor me. )

Nevertheless, I feel obligated to point out a major flaw, not in the mathematics, but rather in the reasoning: the 'experts' are comparing MPG in the Prius to MPG in a 'comparable' new automobile. It's not (I'll just say) "fair" to compare your number, using an 89 Pathfinder (or my number, with a 92 Olds Ciera) to the 'experts' number, using an 04 Corolla.

If you really want to do a valid comparison to your Pathfinder, you'll need to recover, in gasoline, the entire cost of the Prius minus the cost of anticipated repairs on the 89 Nissan.

We get so frustrated when publications misrepresent the capabilities of Prius; we've got to be careful not to fall into the same traps on the other side.

Cheers,
Brad

p.s. Yeah, I know: what is "comparable" to a Prius?

p.p.s. What could a Prius get in MPG if there were no battery? Hmm...

[finman]

Ya know, I realized that mistake shortly after posting my calculations. Yes, it's true. Must compare apples to apples, etc. I just wanted to show that conserving gas is good and doable. Lots of other factors I didn't figure should be considered, as always. I was really blown away with the gallons saved figure (700 gallons). That right there told me I did the right thing. Less polution, less foreign oil going into my tank.

I wanted to keep it simple for my sake when doing the comparison. I did not have a car payment with my old truck, had lower insurance to pay. I rode my Harley more ('cause it was more fun). Now I think the Prius is more fun, (sorry Harley riders!). It has a better stereo and heater. I definitely believe the Prius is in a class by itself...

[kjb516]

Nevertheless, I feel obligated to point out a major flaw, not in the mathematics, but rather in the reasoning: the 'experts' are comparing MPG in the Prius to MPG in a 'comparable' new automobile. It's not (I'll just say) "fair" to compare your number, using an 89 Pathfinder (or my number, with a 92 Olds Ciera) to the 'experts' number, using an 04 Corolla.

Another reasoning flaw I've found with breakeven calculations, is the wrongful assumption made by many that use current gasoline prices to calculate future savings.

Having detailed records of my fuel purchases over the last three years, a simple graph of gasoline prices over time with a linear trend line into the future indicate a price in excess of $3.50 a gallon by July 2011 (my current expectations for keeping my Prius). Personally, I believe that a linear trend is too optimistic and the price will more than likely be around the $5.00 / gallon exponential trend line predication.

[karmavore]

While no one can dispute that gasoline prices will go up, the price increases we've experienced throught the last 20 years have been almost completely due to inflation. Since we're not adjusting future dollars for inflation, using today's gasoline prices certainly seems reasonable. (Using three years of history to project out seven years certainly does not.)

See this chart of Gasoline Price History for evidence of what I'm referring to.

I don't mean to start a debate on Hubbard's Curve, oil, and the like. I do believe gasoline prices will increase, relative to inflation, above the level of the '80s. I only assert that we don't know exactly when this will happen, though it's a good bet that the bulk comes after current owners have already hit break-even, and therefore not necessary to include in this calculation.

Brad

[ssmithri]

Greetings... I am a newbie to this site and a new Pirus owner.

I do not know all of the intricacies regarding mileage calculations, etc..., but I do know one thing. By the time I will have to fill up my Prius for the frist time (around $20.00-the dealer gave me the first tank), I would have had to fill up my SUV five times ($60.00).

Calculate it any way you want. This is cash in my pocket.

:mrgreen:

[TonyPSchaefer]

Greetings... I am a newbie to this site and a new Pirus owner.

I do not know all of the intricacies regarding mileage calculations, etc..., but I do know one thing. By the time I will have to fill up my Prius for the frist time (around $20.00-the dealer gave me the first tank), I would have had to fill up my SUV five times ($60.00).

Calculate it any way you want. This is cash in my pocket.

:mrgreen:

Leave it to the "newbie" to keep things in perspective. I admit that sometimes we over-analyse things a little too much. I started working in the "oil change every 3,000 vs. 5,000" as well as the estimated repair costs but figured my time would be better spent doing anything else.

Welcome to PriusChat, ssmithri! I hope you find a lot of good information here and stick around a long time.