Amy's Tire Question


On the November 3rd, 2007 show, Amy asked why the pressure doesn’t go up in a tire when the tire is loaded, compared to when it is off the ground.

Click and Clack had a Physics professor call in - and his answer was exactly right: It does change, but the change is undetectable because of the accuracy of the pressure gauge.

First it’s the precision of the gauge, not accuracy (accuracy refers to how close to the correct value the measuring instrument is), but other than that the answer was correct.

In order to verify, all you need to do is buy a pressure gauage that measures to the nearest 0.1 psi. There are plenty of gauges that do so, but they are a bit pricy.

Here’s what you will find: On a typical passenger car, the increase in pressure will be in the 0.2 to 0.5 psi range - not enough to detect with the typical pencil gauges.

Try it for yourself - there’s no need to use 100’s of pounds of sand bags.