At any given moment, I know to within half a pound what the tire pressure is in the race car I’m driving. There’s a guy on our team whose job is to monitor and adjust those pressures to get the most out of the tires given the ambient temperature, compound, and length of the course before the next pit stop. He checks pressures probably a hundred times in a single day.
On my street car, I’m pretty sure I checked the pressures as recently as 2009.
That’s irresponsible, and it’s because I’m lazy. But that doesn’t make it ok. In fact, after filming the piece above, I was inspired and actually checked the pressures on my car. After digging around in the glovebox, underneath expired insurance docs and spare fuses and, actually, a pair of gloves, I found the pressure gauge. And then I had to remind myself what the pressures are supposed to be.
That’s always the first surprise. Most modern cars require pressures around 30 pounds per square inch (psi) on all four corners. But the sticker on my 1982 Porsche 930 reads like a guide for an all-inclusive resort in Cancun: 2 bar in the front, and 3 bar in the back.
“Bar” is the European way to say “100 kilopascals,” which is a pretentious scientist’s way to say roughly atmospheric pressure. So, at sea level, we live at one bar. Like Norm in Cheers.
Atmospheric pressure is about 14.5 psi. So my Porsche wants twice that, or 29 psi, in the front tires, and three times that, or 43.5 psi, in the rear tires.
See why I don’t check tire pressures much? It’s all the math.
Anyway, this difference front-to-rear on my car is because it has a very heavy tail – I mean, worthy of a Kardashian. 63% of the car’s weight is on the rear tires, hence the 43.5lb recommended pressure.
I found that my fronts were at 27lb, and my rears at 34. That’s 2lb low in front, and almost 10lb low in the rear. Couldn’t see it just looking at the tire though – had to use the gauge.
So I put them back up to the recommended pressures and – know what? The car worked better. It handled better, it rolled more easily coasting to a stop, and I presume my fuel economy increased (hey, I’m lazy enough to let my tires get 10lb low, think I’m diligent enough to compute my fuel economy?). Damn those German engineers. They’re right again.
Moral of the story? Get a guy who checks your tire pressures a hundred times a day. Or at least dig out a gauge and check your own once a month or so.
Do as I say, not as I do.
PS: The Corvette pressure/fuel economy test in the video is unscientific, we know. But the results are what we actually got on the same piece of road at the same throttle opening and speed. I was just amazed that there did appear to be such a difference.
PPS: Don’t ever take both hands off the wheel. I was explaining something really complicated to you, okay?