I have Direzza Star Specs with 5000 miles on them and the rear passenger tire does not hold pressure at 31. The pressure slowly decreases to 25 and stays there. Any thoughts on why this is happening?

 

A leak.

 

awkward, since it stops leaking at 25 psi. i routinely check my tires and it does not leak below 25 psi.

 

A small leak can do that sInce the higher pressure forces it out a pinhole. Bring it to a tire shop to check/patch it.

 

I bet if you did some hard cornering it would decrease from the 25. to confirm

 

My buddy had the same issue a few months back. We took the wheel off and there was a screw in it.

 

slow puncture i think too.
mine holded fine 38-39 psi.

 

puncture or stem leak/valve

 

The only other issue other than stated above is that it could be leaking at the bead. Spray the bead (inner/outer) with some soapy water in a spray bottle, if it makes a bubble you've found it. This will work for finding punctures to, just fill the tire to it's max pressure prior.

 

although its not as common as a puncture people do often over look their valve stems. if i was you i would take the wheel off over fill it to about 40 and start spraying it down with water to c if there are bubbles coming from anywhere.