Most portable car air compressors seem to have ditched the quick release attachment for Schrader valves in favor of a simple screw on attachment. Both of my bike's tubes leak a lot of air while I unscrew the compressor after filling them. Am I doing something wrong? Is there a secret to disconnecting a screw fitting without draining half the psi in the process? Why are there no quick release attachments any more?
These compressors are intended for cars, and because of the much higher volume of air in those tires, they won't lose enough air to matter when unscrewing them. As noted by another poster, you can get a replacement head with a Schrader valve. Some of these compressors have a crimped-on end fitting, so to replace them you would also have to get a suitable crimp and crimping tool, although a barb-type with a hose clamp will also work. These compressors can work well for bikes, as most won't compress above around 125 psi, which, while much higher than is appropriate for many tires, is not likely to blow the tire off the rim if you get distracted while inflating. However, some go as high as 200 psi, so you will have to pay attention. I would agree with another poster, though, and get a good floor pump and throw it in the car. I think the Silca Super Pista is the best out there for bicycles. They are not inexpensive, but will last a lot longer than the car inflators, and they provide a bit of upper body exercise in the process.