Make sure you read the side of the tire. Should say max psi ____, this psi reading is when you veichle is at rest for atleast 3 hours. Be careful to not over inflate them. If you do the tire will pop right out of your wheel. When you drive your car the tire gets hot. Heat inside the tire makes the tire psi go up. So if your max pressure is 40 keep it under 40. I have yokohamas tires. Max pressure i belive is 40. When my car is at rest is 35. after driving a few minutes my psi when up to low 40. Hope this helps.