1997 Mazda Miata: Two Valve Stems, But Why?
February 13, 2013
I first noticed that the alloy wheels on our Miata had two valve stems when we last tested it and I intended to do a little research to find out why.
Of course, by the time I got home, I forgot to look this up. At the time, I suspected it was to purge condensed water from one side while filling the other side with air. Not exactly.
According to the wheels' manufacturer, 949 Racing (whose name denotes Lake Forrest, California where they are located), "This makes it possible to perform a complete nitrogen purge. You may notice many high-end tires stores now offer nitrogen. Nitrogen doesn't fluctuate pressure as much as your tires get hot and they hold air much longer. With a single valve, you still have some atmosphere in there when inflating with nitrogen. Two valves = 100% nitrogen."
Now you know. And I can get some sleep.
Chris Walton, Chief Road Test Editor @ 140,814 miles