Tire pressure when is hot?

:
mazda
When vehicle is driven, what pressure I should inflate the tires to?
One guy at tire shop said +3psi - so 38psi - the guy inflated said it will be bumpy.

When I was on freeway (38psi) it felt as if I didn't have the benefit of the tire (it was so hard) - car was not gripping the road. Besides stuff inside the car was vibrating from time to time.

So I used the nails to release some - measured it after driven on freeway and it was 36psi all around!

Should I inflate to 35psi regardless? What do you guys do?

Update:
2013 Sport - Manual says 35psi
At 38psi - heard resonating vibration
 
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You're supposed to measure the tire pressure when the tire is cold. If you've driven the car, you'll want to wait overnight, or at least wait a few hours. Factory pressure for the 06-10 is 37psi cold. 1-2 psi variation isn't going to make a huge difference in ride quality.

I measure treadwear and adjust my pressure accordingly. Different tires behave different ways, plus your driving style might dictate a need/want for different pressures than everybody else on the forum. Go with factory pressure after the car has sat overnight, then adjust from there.
 
I run my summer and winter sets at 38-40 psi when measured cold. (I think it was a recommendation of a few mechanics and other folks at some point so I just stuck with it.) So far wear is even and performance is good too. I don't measure every day so some days depending on weather/conditions, actual pressure when cold could be outside of that range. But like p.b mentioned it should not make noticeable difference when driving.

If you are having issues there may be something going on related to the suspension outside of tire pressure. Perhaps wheels are out of balance? That is not unusual -- good to check once in a while and adjust. Perhaps a wheel has damage? Maybe a suspension part is loose or worn out?
 
2012 touring. 102,000 miles using 225/45/18 tires. Run them at 36psi all their life. First set of OEM tires lasted 38,000 miles. Second set of tires lasted 51,000 miles. On 3rd and final set of tires now.
 

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