Always make your checks when the tires are cold -- all specifications (the car manufacturer's recommended pressures, the tire manufacturer's maximum pressure) assume cold pressure measurements. They both know that the pressure will increase after the tire is driven a while, so don't worry about possibly going above any specifications when the tire is hot -- it's supposed to do that.

Probably better to check when cold, but you can do it after you have driven. Just subtract about 3-4 psi to obtain a cold pressure. For example, if you want a cold tire pressure of 35 psi (normal), your tires might read 39 psi since the tires are hot. Make sense? If you want 37, fill to 40 at the gas station.
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Patrick McHugh, Cincinnati, OH, 1993 244 Limited Ed. 'Classic' model (daily driver)

I always check in morning after car has been sitting overnight. Also when there is snow I set them about 2 to 4 pounds less as that way I get a little better gripping/traction. A lot of folx only check their tires maybe every few months or so. I check my tires every two to three weeks. Hope this helps.

Best time to check is when cold meaning the car hasn't been driven in a few hours and the tires haven't been heated by the sun. Like when the car has been parked in the garage or carport. Don't laugh! I get a 2 lb. difference between the southern side and the northern side. I found that the newer digital gauges give a better, more consistent reading than the spring activated pencil style. Maintaining tire pressure at the level recommended by the mfg improves gas mileage, makes your tires last longer, helps the car handle the way it was designed to handle and improves safety. At no time should pressure exceed the tire mfg's max pressure, but usually that is far above the car's requirement. Sometimes there are two pressures, a higher one when fully loaded with passengers. It doesn't hurt to have tires at that pressure all the time, the car will just ride a little harsher.

Cold. I've seen this described (Tire Rack? Car Owner's Manual?)as being within a mile after starting out cold.

I have personally checked tires that had identical pressures in my driveway in the cool morning, show pressures 4psi higher on the side that was in the sun, by noon, relative to the other side! The tires were too hot to leave your hand on them long, compared to the shaded tires which were merely warm (ambient air temp).
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD; hobbycar 77 MGB, and a few old motorcycles)

As I recall, don't know from where, the best time is in the AM before driving anywhere. Pressure needs to be below the max, as it will go up with warming up.

Regards,

Bob

:>)

I believe its best to check the pressure while the tires are cold.