May 1, 2008

How to save on gas #3 - Don't drive too far out of your way to save a nickel on gas

Gasoline is getting more expensive all the time. So many of us are looking for ways to save a few bucks on gas. One obvious way we might try to save on gas is to buy at the cheapest station. If the station by my house is currently charging $3.45 for regular and there's a station on the other side of town charging just $3.29 then I would prefer to buy at the cheaper station right? If I have a 15 gallon tank and fill up for about 14 gallons then I'd be saving $2.24 every time I fill up. But what if that other station is 5 or 10 miles out of my way? Remember that it costs money in gas to drive out of your way. Before you consider driving out of your way to a cheaper gas station, figure out how much it will cost you in gas to do so.

As a simple rule of thumb: I would think first before driving more than 1 mile round trip out of your way per 1% difference in the price of gas.

This is a rough rule of thumb and the exact break even point is going to depend on the size of your gas tank and the MPG rating of your car. But the 1 mile per 1% cost rule of thumb is close enough for ballpark figuring and relatively easy to remember.

For example if the gas is 5% cheaper then don't drive more than 5 miles to buy it (2.5 miles each way). Say gas is $3.20 closer and $3.14 farther away (5% difference) if your car has a 15 gallon tank and gets 20 mpg then by driving 5 miles you'd be using $0.90 in gas to save $0.78 on the fill up, which is only a $0.12 savings.

To figure your own exact savings you need to know your own cars MPG rating and your cars gastank size. The gastank size is often listed in the owners manual. You can figure your actual MPG by measuring your mileage on your odometer and dividing by the gallons you use at a fillup, but do this over several fillups and average out the results.

You can figure savings of driving for cheaper gas using the following formula:

Savings = ( Expensive GAs - CheapGas ) * Gastank size - (Distance driven / car MPG) * Cheap gas

In the last example that would be:

= (3.2 - 3.14) * 15 - (5/20) * 3.14 = 0.12

What I would recommend instead of driving out of your way is to shop the cheapest gas station that's in your normal driving area. OK so what do I mean by "normal driving area"? I simply mean the places you normally go. This would include your path to and from work, your route to the grocery store and any other places you normally visit. Look for any of the cheaper gas stations in your normal driving areas. Then look to see if any of the cheaper stations are a little bit out of your way from your normal trips.

So lets put it all together and do a comparison example between driving too far out of your way and just staying in your normal driving range. Lets say my car has a 15 gallon tank and I fill up for 14 gallons at a time and it gets 20 mpg. I drive to and from work every weekday. Its a 3 mile trip each way. There is a grocery station right on that trip that is $3.45 right now. But if I drive just 1 mile out of my way on my way home I can swing by the local Costco and fill up for $3.27. That 1 mile extra only costs me 1/20 gallon ($0.16) and I will save $2.54 total filling up at Costco less the cost of travel. If however the only Costco was 16 miles out of my way then I'd be spending 16/20 gallons = $2.62 in gas for the round trip and actually only saving $0.08 to fill up at the cheaper station by driving too far to do so.

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