You can't always judge a tire's inflation pressure by appearances alone. By the time a low profile radial tire appears to be low, it may be 10 to 15 psi underinflated.
According to a recent survey by the Car Care Council, 54 percent (that's over half!) of vehicles inspected during National Car Care Month were found to have improperly inflated tires. Most were low, but some were dangerously overinflated, too.
The Government Accounting Office estimates that probably 250 lives a year might be saved by reducing the number of fatal accidents that are attributed to underinflated tires. To read this government report, Click Here.
The point here is that many motorists rarely check the inflation pressure in their tires, and if they do they may not do it correctly. Tire pressures must be checked when the tires are cold because driving generates friction and heat that increases the pressure inside the tires. The outside temperature also affects tire pressure (pressure drops about 1 PSI for every 10 degrees F).
Checking inflation pressure also requires an accurate tire gauge. We've seen cheap tire gauges that are off as much as 6 psi right out of the package. The gauges on many gas station tire inflation machines are even less accurate.