Chris sets us straight on nitrogen filled racing tires.

Dear Car Talk

Dear Car Talk | Jun 01, 1995

Dear Tom and Ray:

I thought you two knew a thing or two. Boy, was I wrong. You two missed the boat on the question of why race cars use nitrogen in their tires. Tire pressure, and the resulting diameter are extremely critical to high performance race cars, especially on an oval track. A high speed Indy car might adjust "stagger," the size of the outer tires compared to the inner tires, by adjusting tire pressure. This makes the car turn slightly, and has a dramatic effect on handling on a high speed oval where cornering speeds are about 200 mph. An adjustment of an eighth of an inch in diameter is a big change on these cars.
The problem with compressed air is that it has moisture in it. And depending on the weather conditions, the expansion of a tire filled with moist air can vary day to day, creating unpredictable handling. So race teams use bottled nitrogen to fill their tires. Race guys are pretty smart. They figured this out years ago, probably when you two were still in diapers.

RAY: You mean in diapers for the FIRST time. My brother's at the age where he's about ready to get back into them!

TOM: We checked with our buddies at the Skip Barber Racing School, and they say you're absolutely right, Chris. It turns out that almost every top professional racing team uses nitrogen in their tires.

RAY: According to the chief mechanic at Skip Barber, the amount of water vapor in the air varies day by day, making the air-filled tires expand unpredictably. Pure nitrogen, without any moisture in it, eliminates that variable.

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