I have a cruiser with 2.125-inch balloon tires which are rated for around 45 to 65 psi, as I recall. I tend to run them in the upper 40s; I check the pressure once a week and they've usually dropped to 40, so a couple of pumps from my floor pump and they're OK again. The problem is with my front tire. It reads 40, I give it the usual amount of air, and the gauge pressure reads...40. I'm afraid to keep pumping, because who knows how much I might end up over-inflating the thing if it's just the reading that's off. The rear tire pumps up to 48 or so as usual, so I'm thinking that the problem isn't with the pump. On the other hand, the front tire never seems to go unnaturally low; it still feels firm, for whatever that's worth, so it can't be dropping significantly below 40 during the week....

Thoughts, theories or recommendations? Something going on in the stem, maybe?