was in a cycle world I read over the weekend. It said valve stems first cause this and to change them every time you swap out tires, also some rubber might be left n the bead area after manufacturing process so remove this too. And make sure the bead of the rim is clean and no nicks or deep scratches are visible. When I did tires and aluminum rims just came out we found that some tire mountinf soaps caused rim leaks so we used wd 40 as a lube and no more rim leaks. Hope this helps any of you wit ha slow leak.