How can you determine tire pressure without using a gauge?

To determine tire pressure without using a gauge, you can visually inspect the tire for signs of underinflation such as sagging or bulging. You can also use the "thumb test" by pressing your thumb into the tire - if it feels firm, the pressure is likely adequate. Additionally, you can listen for hissing sounds indicating a leak or use a tire pressure monitoring system if your vehicle is equipped with one.