Jack M. wrote: Cold temperatures will fool a pressure gauge let alone a TPMS. Our Honda CRV factory system was displaying a fault when temperatures got below freezing, and the Doran Pressure Pro was reading quite low, to the point of 'alarming'. I made sure that all pressures, before travelling were at least even on each axle of the coach, and the same on the CRV. As we started heading south out of Alberta the increasing rolling temperatures became more normal. Now that we are in Yuma the pressures are about right. It is as much about having same pressures on an axle as it is the right pressure. I am considering increasing the Hydrogen from 78 percent to 100 percent as I understand that the pressures will be more stable, and some even profess a better ride.
I've seen this on the external sensors and the internal sensors. However, my SmarTire system is temperature compensated. If the tires get hot it'll determine what the true pressure should be, based upon the temperature, and won't alarm you if not needed. The same when it gets cold, a warm tire, set at 35 PSI will trigger an alert at -10%, which is around 31 PSI. But, that same tire at -10F won't have 30 PSI in it, yet the SmarTire won't sound the alarm because it knows it's cold and recalibrates accordingly. This didn't happen on my Doran or TireSentry systems though because they have no temperature compensation algorithms or a way to even sense the temperature.
Mark Quasius
2007 Allegro Bus 42QRP - Cummins 400 ISL
2002 Jeep Grand Cherokee Overland
2005 Jeep Wrangler Unlimited
I too have experience with the SmarTire system, but you would NOT want it to compensate for lower temps. From the SmarTire website:
"Critical Low Pressure Alert
The Critical Low Pressure Alert warns the driver when a tire's pressure falls below a fixed, user defined pressure level. This audible and visual warning is intended to alert the driver to a critical tire condition in order for them to take immediate precautions.
Unlike the Pressure Deviation Alert, the Critical Low Pressure Alert does not use a temperature compensation calculation. As such, if a tire's pressure falls below the default setting (10 PSI below the cold inflation pressure), the tire truly is critically under-inflated and should be addressed immediately."
If 35 psi is your desired "cold" pressure, this is the pressure required to support the weight of your vehicle, then you always want 35 psi (as measured "cold", even when ambient temps are very cold.
My experience is that a 10°F temp rise results in about a 1 PSI tire pressure rise. The change is so dramatic here in the desert in the summer (70° at night to may 140° tire temp in the sun) that I don't bother checking tire pressures unless it is 4 hours or more since sunset. Just before sunrise works quite nicely.
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