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Maintaining Our Car to Get the Best Mileage

Our car passed 150,000 miles this year—and suddenly became very expensive. First the brakes needed to be replaced, then the catalytic converter, then the tires. But after doing all this work, we’ve noticed a marked increase in fuel efficiency. In January, our car was only getting 40 mpg (or below!), which is the worst it’s ever performed. Now it’s back up to 45 mpg, and I think that’ll rise even more when it finally stops raining.


The Prius’s regenerative braking system uses the kinetic energy from the tires to generate electricity. Because of this, the regular brake pads aren’t used much and last a long time. I think this is the first time we’ve had to have them replaced. Average brake pads are replaced around 30,000–60,000 miles.

I never knew what a catalytic converter did before ours needed to be replaced. Apparently it uses a catalyst to interact with the exhaust and change it to less harmful byproducts. When it becomes clogged, there’s a noticeable change in fuel efficiency. We were told by the dealer that they usually need to be replaced around 90,000 miles, so ours has actually lasted a long time.

Our tires, on the other hand, have been replaced three times in eight years. The first time was because we weren’t rotating them properly, so they wore unevenly. The second time one of them was stabbed in the sidewall. This time the tread actually wore down (finally!).

New tires actually reduce fuel efficiency, at least for a while, because the extra grip means extra rolling resistance. They eventually wear a little and the fuel efficiency increases again. The specific tires we got, Nokian WR G2, are designed to reduce rolling resistance.

As a bonus, the Nokian tires are made with low-aromatic oils. High-aromatic oils are still used as plasticizers in most American tires but have been shown to be carcinogenic, and their use has actually been restricted in Europe, beginning this year. I didn’t even know any of this before we had to replace our tires this time. As long as the performance is the same, why wouldn’t we use the non-cancer-causing tires?

When we got the new tires, the guy at Advanced Tire Company suggested that we fill them with pure nitrogen. It’s supposed to deflate slower than the normal nitrogen/oxygen mix, and it’s used a lot in airplanes and tractor trailers. But I haven’t found a compelling argument that it’s much use in passenger cars, and it’s quite expensive, so we didn’t do it. Jason checks the tire pressure regularly, anyway, before each trip we make to Maine.

What do you think? Do any of you use nitrogen in your tires? Does it make that much of a difference? And is it worth the cost?


Comment from Isabel
Time March 30, 2010 at 10:26 am

We get that question at work a lot (Toyota). It doesn’t make a big difference, so it’s not worth the cost. Air is what is usually used to inflate tires, air is composed mostly of nitrogen (78%), oxygen (21%), other gases ( 1%). By filling them with pure nitrogen the only thing you’re doing is squeezing out that small amount of oxygen that is already present in the air surrounding us. That amount of oxygen is so small that it doesn’t even cause oxidization inside the tire. Nitrogen does leak out of the tires at a slower rate than oxygen, but making sure your wheels are aligned and checking your tire pressure weekly (if you drive a lot, if not every other week) will save you all that money and you’ll get the same results.

Comment from Isabel
Time March 30, 2010 at 10:31 am

Also, make sure you rotate your tires every 5,000 miles. That will prevent them from wearing out unevenly.

Comment from Brenda Pike
Time March 30, 2010 at 2:27 pm

Thanks, Isabel. It’s nice to have an expert weigh in!

Pingback from Friday Green Links – 7/1 « Pragmatic Environmentalism
Time July 2, 2010 at 2:58 pm

[…] to Lower Resistance – Boston Globe. Our Nokians weren’t on the list, but it’s good to see Consumer Reports factoring rolling resistance […]

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