Dear Tom and Ray:

So many of my friends evaluate the cost of a car trip only by the cost of the gas. But I know that the cost, given wear and tear on the engine, oil changes, tires wearing out, alignment, etc., is actually much, much higher. I know this depends on the car, but how much, on average, does it cost per mile to run a car?

-- Rachel

TOM: Well, every year, the Internal Revenue Service answers that question. They want to know the value of one mile driven in the average car so they can let taxpayers know how much they can deduct for business use of their personal vehicle.

RAY: The number they came up with for 2014 is 56 cents a mile.

TOM: Now, let's say the average car gets 25 miles per gallon today, and the average price of gas per gallon is $3.50. That means that gasoline represents only 14 of that 56 cents.

RAY: And the rest -- the other 42 cents -- covers wear and tear and insurance.

TOM: In reality, that maintenance-and-repair figure will be even higher on pricier cars. Because if you're driving a Lexus or a Lincoln, the price of your maintenance, repairs, tires and even insurance is going to be even higher.

RAY: But that 56-cents-a-mile number gives you an idea of how much people underestimate the cost of operating a car when they factor in only the 14 cents' worth of gas, Rachel.

TOM: So next time you drive your friends to the mall, you can try hitting 'em up for the full IRS reimbursement. See how that goes over. And be prepared to settle for a grande cappuccino.