
A tire will really pop when inflated, but the gauge doesn't change when you inflate it. I attached the pump to the tire; The pressure gauge showed the exact pressure in the tire. Then I turned on the pump. I left it on for a few minutes and the sensor didn't move. I figured the pump wouldn't work even though the engine was running etc. but removed it and attached a pop up pressure gauge to the tire. I found that the pump actually added a few pounds to the tire, it just didn't show on the built in pressure gauge. I don't know if this is just a defect in what I have or if everyone does it. Otherwise, the pump is fairly compact, about the size of a small (thick) hardcover book.