Originally Posted by
DiabloScott
Or it could be that you're introducing error when you measure the pressure loss.
+1
By the time you burp the valve (if applicable) and stick the pump head on you've lost at least 10 pounds on a narrow road tire.
If you're really losing 20 pounds every 1-2 hours (15 mile ride...) then your tires would be completely flat in a day and you have a slow leak to address,