Fuel Considerations

After reading some posts on high mileage Toyotas, I wanted to write this,
and it just got longer and longer.

Let us play with some math, by defining the following definitions:

mpg = miles per gallon (m/g)
c = cost per gallon (c/g)
m = miles
g = gallons
t = total cost in fuel

Then the total cost in fuel is:
t = m / mpg * c

A vehicle's gas mileage is:
mpg = m / g

Let's assume Truck A gets 15 MPG, has been driven for 300,000 miles, and
gasoline is a *very* conservative $2 per gallon. Then the total cost of fuel
is:
t = m / mpg * c
= (300,000 miles / 15 MPG * $2 per gallon)
= 2 * 300,000 / 15 dollars
= $40,000

Now let's do the same with Truck B. Truck B gets 30 MPG, and everything else
is the same - it is driven for 300,000 miles and gas is still only $2 per
gallon. Now, the total cost of fuel is:
t = m / mpg * c
= (300,000 miles / 30 MPG * $2 per gallon)
= 2 * 300,000 / 30 dollars
= $20,000

So, how would a person calculate the fuel mileage for a vehicle? The key is
in noticing that fuel mileage is noted in "miles per gallon," or m/g. Start
by filling the vehicle's gas tank to the top, drive until the tank is empty,
and take note of the miles driven on that trip.

If the vehicle starts at 110,234 miles on the odometer and reads 110,492
miles at the next fill-up, the vehicle has traveled (110,492 miles) -
(110,234 miles) = (258 miles).

If the vehicle took 8 gallons of fuel to fill, then the fuel mileage is
roughly (258 miles) / (8 gallons) = 32 MPG.

This is not very precise, because people will stop to fill the fuel tank at
different levels of "tank emptiness" and the tank is not always filled to
the same level of "tank fullness." But, if a log of the fuel mileage
calculations is kept every time there is a fuel fill-up, the average MPG can
be calculated.

Further, by keeping a MPG log, when the MPG suddenly drops for no known
reason, the vehicle is having problems (or the math was wrong)!

A lot of people think they are going to save money by buying a motorcycle,
which (on average) get about 40 MPG. Keep in mind that a new motorcycle will
cost $10,000 or more (not counting the monthly insurance of $75 or so). If
that person's daily driven vehicle gets 15 MPG, then their miles per gallon
savings is (40 MPG - 15 MPG = 25 MPG).

How far would someone need to ride a motorcycle getting 25 MPG better to pay
off just the cost of the motorcycle?

The calculation for total cost can be worked from the same equation as
before, by using Algebra to flip some of the numbers around:
(t = m / mpg * c) is the same equation as (m = t * mpg / c)

Using the MPG savings of 25 MPG, we see:
m = t * mpg / c
= ($10,000 * 25 MPG / $2 per gallon)
= 125,000 miles

What does this mean? It says that someone will have to drive a motorcycle
for 125,000 miles just to break even with the $10,000 they paid for it. To
actually save money, the would have to drive that motorcycle further. Again,
that does not include the price of insurance on a motorcycle, which will
just add to the pot.

Sometimes, it is interesting to look at the math to see the reality.

So, if someone tells you they bought a motorcycle to save money, look back
at them and just laugh, because they probably have not done the math.

Regards,
Joe
Software Engineer
BS in Physics
BS in Mathematics

"jp2express" <jp2mail-tempforum.DeleteThis@noSpamyahoo.com> wrote:

>After reading some posts on high mileage Toyotas, I wanted to write this,
>and it just got longer and longer.
>
>Let us play with some math, by defining the following definitions:
>
>mpg = miles per gallon (m/g)
>c = cost per gallon (c/g)
>m = miles
>g = gallons
>t = total cost in fuel
>
>Then the total cost in fuel is:
>t = m / mpg * c
<snip>
>
>Using the MPG savings of 25 MPG, we see:
>m = t * mpg / c
> = ($10,000 * 25 MPG / $2 per gallon)
> = 125,000 miles
>
>What does this mean? It says that someone will have to drive a motorcycle
>for 125,000 miles just to break even with the $10,000 they paid for it. To
>actually save money, the would have to drive that motorcycle further. Again,
>that does not include the price of insurance on a motorcycle, which will
>just add to the pot.
>
>Sometimes, it is interesting to look at the math to see the reality.
>
>So, if someone tells you they bought a motorcycle to save money, look back
>at them and just laugh, because they probably have not done the math.
>
>Regards,
>Joe
>Software Engineer
>BS in Physics
>BS in Mathematics
>

<snip>


OK, so in 2002 I bought an 86 2WD for $1000 with a rebuilt
engine, new radiator and water pump from a family member who
had an auto repair shop and loved Toyota pickups. In the
last four years driving 32,000 miles, I've put four tires on
and had a clutch job for a total of another $1000 or so.
Then about $250 a year insurance.

So my total "hardware" investment has been $3000 over four
years.

I get between 24 and 28 mpg. The truck has 360,000 miles on
it. Starts after about a half second. Burns a quart in about
1000 miles.

Hard to get rid of this truck, but I got a Prerunner and am
very happy with that.

But the 86 has been just incredible. We use it now just to
haul trash to the dump.

This does qualify as a money-saver, correct?

- Bob