The tire pressure sensors are temperature compensated and will not read the same as a normal (not temperature compensated) tire pressure gauge. If the tires were pressurized to 42 PSI at 70 degrees F for example, when the temp. drops to 40 F the pressure will drop to something like 39 PSI, which an external gauge will show. The TPS sensors will continue to show the pressure is something like 42 PSI at the lower temp. So if you inflate the tires to the higher pressure at a lower temperature, the TPS will show a higher reading because of the low temperature.
The reason the sensors are temperature compensating is so that the pressures do not read very high when riding the bike- it would tend to put the owner off and would probably lead to him / her stopping and reducing the tire's pressure while hot (which is not the right thing to do). Compensating for temperature is a judgment call that the chip manufacturer made when designing the controller.
Brian
Ok so get up at zero dark thirty and it's hella cold out there, and in the garage. I just returned from six weeks in Southeast Asia so my bike has sat all that time. Everything looks fine, tires appear hard, and I'm out for a short ride. Fire up the bike (whew, it still cranks) and take off. TPMS shows 38 F 41 R. A tad lower than I want, but fine for now.
The bike just doesn't feel right. Steering is heavy, it just feels off. Granted, I've been tooling around on a 125 cc Honda Elite motorbike for the last six weeks, so I chalk it up to that. Later in the day, when it's warmer and I feel like screwing around in the garage, I fire up the compressor so I can fill all tires that need filling. My slime gauge reads 32 F 38 R (WTF?) so I fill it back up to 42/42, which is where I like it. Get back on the bike. Rides like it should, feels good again. TPMS is reading 47/47.
TPMS so far has been fairly accurate, to within a couple pounds of a gauge, but for whatever reason it's really off now. The only thing that is different between now and six weeks ago is that it was a whole lot warmer outside. Anyone else notice that?