Tire pressure monitors and good tire gauge

TPMS showing low pressure..so I bought a NEW gauge and adjusted the pressures 30 front 38 rear, 18" wheels on a 2007 BASE
THIS WAS WITH WARM TIRES....ambient temperature 87, 5 mile low speed drive. (I figured a few pounds more for the heat)
Monitors show 42 on one rear 40 on the other, 35 on one front 33 on the other...(the sensors were checked in December when the new Michelins were installed)
What would be the absolute best most accurate gauge to buy?
How much more to add for warm tires?

CR rates the following as 3 as being most accurate and easy to use:

Accutire MS-4400B

Accutire MS-4021B

Intercomp 360060 (pricey)

This is almost as accurate

Accutire MS-4004B

I see about a 3 psi difference between cold and warm tires. I'd imagine it can vary though, depending on ambient heat, road surface, and driving conditions.

PV=NRT is the only true answer. And since N and R don't change, and V changes little, then P is proportional to T, in Kelvin.

For Kelvin, convert to Celcius, then add 273 degrees.

But you need to know the before and after temps.

Check them COLD before you drive, then simply add X pounds (when you get to the gas station) to those that need it.

Or, overfill, drive home, lower tomorrow.

Accu-tire will calibrate your mechanical gauges. The strain variety are generally more accurate and dont drift as much.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I like to check tires after the car has been sitting overnight. They should be checked when they are "cold".

Just having one of side of the car sit in the sun can cause pressure to rise by a PSI or two on that side.

If you have them set at 70 F and temps drop to 40 F, the pressures can easily drop by a couple of PSI.

Driving at high speeds or pushing in the twisties can push the pressure up by 4 or 5 PSI. There are lots of variable. That's why you should set the pressures when tires are "cold" for consistency.