Originally Posted by Calsun

I would replace the tubes and check that the new tubes are not leaking out the valves. The lighter "race" tubes wil be thinner and there will be more permeation with air leaving through the material. I would check that the valves on your tires are tight and use a valve core tool to tighten them. The Park Tool valve tool is cheap and works on both Schrader and Presta valves.