What Does an 8% Fuel Economy Improvement Do for the Family Car?

June 23, 2009

 "Up to 8% more fuel efficient to save you money," claims the Michelin tire ad. Yep, it's bill-paying time in my house, and this caught my attention. Can changing my old, run-down tires to Michelin® Energy™ Saver A/S Tires save me money? How much impact does 8% have on fuel economy?

Disclosure: I found this information right on www.familycarguide.com, in an advertisement paid for my Michelin. I'm just danged curious today, and for some reason, I'm feeling the itch to play with a calculator. There is no other incentive for me to post this, and please don't take it as an endorsement of these tires. I currently have Kumho tires on my Pontiac Vibe, and they've served me very well.

So what's the calculator exercise today? We'll visit three popular family cars and look at the stated MPG and apply that 8% increase to see the impact play out in real life. Simple! Let's see if it's worth it to buy those tires...

2009 Honda Odyssey:  Scoring a 10 out of 10 from TheCarConnection.com, the Odyssey is a hugely popular minivan for those school drop-off/pick-up lines. That 16 MPG city rating gets a boost to 17.28, and the 25 MPG highway becomes 27.

Let's stick with the highway mileage for a minute. Assuming you drive 15,000 under those conditions, you'd use 600 gallons of gas at 25 MPG. By leveraging that 8% increase, you'd only use 555 gallons of gas. Based on the price of gas on June 22 (national average), that's the difference between paying $1,614.60 at the pump versus $1,493.50. You'd save $121.10 each year by increasing your MPG from 25 to 27.

2009 Chevrolet Suburban: The Suburban is available with a "flex fuel" system, meaning it can take either traditional gasoline or E85, which is 85% ethanol. So, these gas mileage numbers might see the same increase, since the idea here is more a function of improving the tires, and not the powertrain. But, the only published numbers I have to work with are the traditional powertrain. So, we have to start with 20 MPG in this case. With the 8% increase, that's 21.6 MPG highway.

Same math applied, you'd spend $2,018.25 to put 750 gallons of gas in your Suburban if you consumed it at a rate of 20 miles per gallon. Otherwise, you'd spend $1,868.75 for 694 gallons of gas. That's a savings of $149.50 each year.

 2009 Toyota Highlander: Holy moley, TheCarConnection.com lists 21 ways you can order this family vehicle.  One of the options is a very ample third row that still leaves room for a little cargo. It's easy to see why larger families pick the Highlander. Oh, and there's a hybrid Highlander, too. Highway gas mileage seems to range from 23 MPG to 24 MPG, so we'll just give it a bit of a boost and run with 24.

In case you couldn't tell yet, I hate decimals, except when we're talking money. So, that 8% boost takes 24 MPG to  25.92 MPG. Forgive me, this is a random exercise... I'm using 26.

The Highlander would then cost you  $1,681.86 to put 625 gallons of gas in the tank each year. With the 8% MPG increase, 577 gallons of gas would cost $1,552.50 each year. You'd save $129.36 in gas costs each year.

Okay, now that we've put some numbers to this, does an 8% increase in MPG appeal to you? Remember, tires last more than a year. Also remember that I used the most advantageous numbers, the highway ratings. Otherwise, it's a little hard to see a difference, kinda like splitting hairs. This is completely not conclusive, and involved me using standard MPG ratings and a calculator. Your results can be wildly different.

But, hopefully it'll give you a chance to stop and think about gas mileage. Maybe 8% sounds tiny. Maybe it sounds huge. You decide.

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