Test your tire when it is at a neutral temperature. In order to do this you will need to test the tire in a covered area and when it has been driven for no less than two hours. Place your bare hand on the tire to ensure that it is cool to the touch.
Place a penny into the groove of the tire tread to test the tread depth. If the tread comes up to the middle of the head of Abraham Lincoln then your tire will give an accurate reading. Low tread depth will give a low reading on your durometer.
Remove any dirt or stones from your tire by running the flat end of a scraper along the tire tread surface. This will remove any type of barrier that may come in between the durometer and the tire contact.
Apply the base of the durometer to the tire using firm and even pressure. Do not tilt the durometer during the reading process as this will distort the final reading accuracy.
Note the number that the durometer comes to quickly and stabilizes at. This will be your reading number. If you test another section of the tire, it should read the same. The durometer will measure from 0 to 99. If the number is low then the hardness of the tire is low. If the number is high then the harness is high.