Comment on an RV forum
"I just bought a new TST 507 TPMS (tire pressure monitoring system) and I gotta say they could improve the documentation.
Definitely confusing as setting up is a bit complex. At one point you
are told to press a button and wait for the second beep (not the first!)
before setting the pressures or whatever.
But once that's over, it works as advertised. It does seem to take a
while, once turned on, for all the sensor readings to be displayed.
After that it just cycles through them every 5 s, and beeps when one is
over or under.
Not sure how accurate the psi readings are. Will have to get out my pressure gauge and compare."
TPMS are primarily designed to WARN of a loss in pressure and
are not intended to be your primary source of accurate pressure
measurement. In my experience ALL TPMS will have one or more sensors
reading a psi or two different than a hand-held digital gauge. For that
matter even hand-held gauges are seldom accurate to +/- 1.0 PSI based on the calibration checks I offer at my tire seminars.
best practice is to set your tire pressure as close as possible to the
desired CIP (cold inflation pressure) using your personal, master digital hand gauge and then install the TPMS sensors.
Wait about 5 min for pressures and readings to stabilize, then do a pressure check on the monitor. You will note slight variation, but all should be within
the specified range (some spec +/- 2% some spec +/- 2 psi) You will
find that after a few days use you will get comfortable with the pressure
readings showing some variation from each other. With a little
experience you will get comfortable and know the range of normal
What I do...
Each morning when I get up, I first turn on the TPMS
monitor and go get my coffee. By the time I am done with the 1st cup -
about 10 min - all the sensors have sent in a reading. I step through
each tire on the system and based on experience, I know if the tires are
ready to go as far as being properly inflated. Yes, the numbers vary, but
as long as they all are in a range of a couple psi from what I got when
I last set the tire pressure all is good.
With the above practice I
am getting the "cool tire" pressure reading which is the only reading of
importance. With my +10% over the minimum inflation needed for my
Motorhome, I don't have to worry about a daily +/- 2 to 4 psi variation.
However, if I have a few days in a row with the display pressures
consistently showing a few psi lower than my CIP goal I know it's time
to plan on a stop at the truck stop for a shot of high pressure air.