It’s normal for tire pressure to fluctuate by 1–2 psi from time to time.
Just curious—why are you running lower pressure in the front?

 

That's what the label on the drivers door post says to run 32 psi on the fronts and 33 psi on the rears.

 

Page 510 in the owners manual also has the pressures.

 

OK. I've got it backwards. I did measure 32 psi in the rears and 33 psi in the fronts. I get silly things mixed up from time to time.

 

the temperature and different calibration on the tpms sensor may have 1-2 psi difference, to be very accurate just use same pressure gauge to measure all tyres.

 

TPMS is not meant to be an accurate tire pressure data source. It's meant to alert you if the tire pressure gets too low (I don't think it alerts for too high tire pressure). You still need to manually check and adjust your tire pressures at least once a month.

 

I need to do a manual check and let some air out of the tires now that the cold season is well and truly over here.

 

After settling into everyday use, I use tpms regularly; as I'm scrolling the driver's display for Shirley (my Google navigator), radio or CD player, tire pressures are displayed for instantaneous monitoring instead of manually using my tire pressure gage in the armrest cubby. When my Xtrek was new, I checked gage values against tpms; variance was + or - 2 psi. I settled on +2 psi over gage value/placard values. Tpms has evolved since it was mandated (2008?) and I think much more accurate when actual pressures are displayed.

BTW, tires on the sunny side will absorb infrared, heating up tires 1-3 psi higher than the tires on the shady side. Once tires are heated up from driving a few miles, tires with lower (standing) pressures increase while the sun heated ones may gain 1 -2 psi.

Which is more accurate, tpms w/digital display or store bought tire pressure gage (none calibrated to NIST)?

 

I check it every day to make sure I’m not losing air. The Impreza has no spare, and the Crosstrek comes with an wrongsized spare, so TPMS is definitely a great tool to have.
Tire pressure readings also vary with temperature—for example, if you’re driving with the sun hitting the right side, those tires can read 1–2 psi higher than the left side.

 

The readings on my 24 'Trek have varied between 30 psi in abject cold (the -10F nights this winter) and 37 psi on the 80+F days here already this spring.

The good news is that in all that fluctuation, they've not lost any noticeably pressure in the 6+ months I've had the car.

 

1-2 psi change is not worth any concern. Something as simple as the sun shining on one side of the car or just hitting one tire will elevate the pressure in that tire compared to the others. The 30 vs 32 could also be a rounding error (i.e. on tire at 30.4 the other at 31.5) where your actual psi differential could be close to 1 psi. Unless you're NASCAR or Formula 1, that psi differential will not affect anything.

 

Speaking of TPM, has anyone replaced theirs due to low battery on the tire sensors. I found that the dealer parts dept charges over a $120.00 each for those. Also has anyone changed their own? I've been to Discount tire and they charge $80 or more to replace just one.
hvaceric@gmail.com

 

Speaking of TPM, has anyone replaced theirs due to low battery on the tire sensors. I found that the dealer parts dept charges over a $120.00 each for those. Also has anyone changed their own? I've been to Discount tire and they charge $80 or more to replace just one.
hvaceric@gmail.com

I've purchased them for snow tire sets and takeoff sets of wheels and tires from a different year that were not compatible. Always purchased name brand such as Schrader, not Chinese knockoffs. Got from Amazon (direct from Amazon not vendors to prevent counterfeits), Summit Racing, and TPMS.com. Rock Auto sells them too so check around. Can be had for $25-30 each. Tire place charged about $10 each to install. Just be careful where you order from to be sure they are genuine. Lots of fakes out there.