“Lauren and I are thinking about driving up to see Bonnie and Kate in Iowa in a couple of weeks,” Julie told me at my kitchen table.

“Are you driving?”

She nodded. “Probably.”

The thought of my daughter, a Kansas University student, making a five-hour trip in the dead of winter to see her twin sister in Iowa City made me worry about the status of her car.

As Julie went downstairs to do another load of laundry, I headed outside.

An icy wind bit into my bare fingers as I checked the pressure on her left front tire. Hmm. Only 28 pounds per square inch. The printing on the tire said the maximum was 44 psi.

Did they leak?

I’d been hearing that putting nitrogen in your tires instead of air could keep them from leaking.

Here’s the deal: Nitrogen molecules are larger than the mix of stuff in the normal atmosphere. That means they won’t seep out through the tire rubber as quickly as regular air, said Steve Aldrich, store manager at Gregg Tire Co., in northwest Lawrence.

Aldrich told me nitrogen has been used for years for race cars and several tire shops around Lawrence offer nitrogen for tires. He installed his own nitrogen machine last September.

“It’s a great idea. I put it in my wife’s tires almost immediately,” he said.

The machine “vacuums” out all of the air in a tire, then refills it with nitrogen. The process takes a few minutes per tire. He charges $5 a tire.

A nitrogen-filled tire maintains its pressure “three to four times longer” than regular air pressure, Aldrich said.

“By maintaining pressure, it gives you better tire life and better fuel efficiency,” he said.

There are other benefits, too, he said.

For example, a lot of newer wheels are made of aluminum alloys. If water vapor gets inside a tire, it can tend to corrode those aluminum alloy wheels from the inside out, he said.

Another advantage of nitrogen-filled tires is they run cooler in the summer, which reduces the chance of a blowout, he said. That’s the main reason it’s used in race cars. (See more about nitrogen.)

Leaking burritos

All of what Aldrich said sounded logical, but I was a little unsure.

After all, the atmosphere already has plenty of nitrogen in it – 78 percent. Oxygen makes up 21 percent, with about 0.93 percent argon, 0.04 percent carbon dioxide and the rest trace gases. I also found some skeptics online, including the Car Talk radio guys.

I asked Joe Heppert, professor and chairman of Kansas University’s chemistry department, about the benefits of nitrogen in tires.

Heppert was skeptical. There’s not really that much difference in the size of a nitrogen and an oxygen molecule, he said.

“You mean like the difference between a baseball and a tennis ball?” I asked.

“No,” he said with a laugh, “it’s like the difference between a Chipotle burrito with lettuce and one without lettuce.”

He explained that each of the two molecules is rod-shaped, within 6 percent of one another in size.

But the difference is their reactivity to metal, he said.

Oxygen could corrode the metal on the inside of the tire, which could cause deterioration over time, he said.

But he pointed out that even if you had nitrogen on the inside of the tire, the outside of the tire still would be surrounded by normal atmosphere, which also includes oxygen.

“Chemically, I don’t see a lot of rationale with filling tires with pure nitrogen,” he said.

I told him I also had another reason for not using pure nitrogen, remembering a scene from the “A View to a Kill” James Bond movie.

If your car goes underwater because Christopher Walken and Grace Jones are trying to kill you, you can always get a few breaths out of the tire stems until they go away.

Pumping up

I drove Julie’s car to the gas station, popped three quarters into the air pressure machine and hurriedly went around to all four tires and made sure they all had at least 40 psi. (Update: A few people have written to me telling me this was a bad idea and the maximum pressure is not the same as the optimum pressure, which is usually listed on the inside sticker on the inside door. I’ve been told that 28 to 36 psi are typical values for passenger vehicles and going over that can result in “excessive wear in the central region of the tread, reduced traction on slippery surfaces and an unnecessarily harsh ride.” Thanks to those safety-conscious folks. )

The sub-freezing cold had reddened my fingers, so I went back home to thaw out a bit.

Getting out of Julie’s car, I looked at my van.

Was that front tire a little low again?

I had the tire gauge handy, so I checked it.

Geez. Only 22 psi?

I was out of quarters. So I went to the garage and got the bike pump and got ready for some exercise.

Maybe I was just hungry.

For some reason, as I pumped, all I could think about were super-tiny Chipotle burritos.