Over Inflation: If your tires are over inflated by 6 psi, they could be damaged more easily when you run over potholes or debris in the road. Higher inflated tires can't isolate road irregularities well, which causes them to ride harder and harsher. However, higher inflated tires usually improves steering response and stability up to a certain point. This is why people who use street tires in track events and road races inflate their tires more than normal. The pressure must be checked with a quality air gauge because the pressure cannot be accurately estimated through visual inspection.
Time and Temperature: Their Effects on your Tires: Tire inflation pressures change due to time and temperature. Tires lose about 1 psi per month due to air escaping through the rubber as it stretches. If you were to check your tires only every six months, it would not be uncommon to find them under inflated by as much as 6 psi. Tire inflation pressures also fluctuate with changes in the outside air temperature. This occurs at a rate of about 1 psi for every 10 degrees Fahrenheit (plus or minus). So the tires you set correctly with an 80 degree ambient temperature will be under inflated by 6 psi at 20 degrees.