This sensor is amazing. The face of the sensor is actually 4 inches in diameter and fits comfortably in the entire palm of your hand. I had trouble with the same 4psi tire setup on my ATV. I pumped it up to 5-6psi and then used the "Prime" button on that gauge to lower the pressure to 4psi. I did it in a very short amount of time, which was nice because the temperature here in Michigan was 19 below with a cold wind.