What maximum pressure are your tires rated for? What do you pump them to? How often to you check the pressure and inflate them? Is it always the same rim or both? Lastly, are you sure the problem isn't elsewhere? That is, you could be losing air through a tiny pinhole leak, so the tire deflates slowly and you get pinch flats. Have you checked for a tiny shard of glass or other small object that you might have missed? Have you check the rim tape?