Originally Posted by
DTSCDS
I have the same problem with my Joe Blow pump. The same tube doesn't give me the same problem with a Serfas pump I also have. On all my tubes I always give it the smallest little 'burp' before I pump, but on this tube I MUST let out enough air to get down to 80-90 or it WILL NOT pump up. The same pump on a REI tube on the front wheel never gives me the same issue. I keep thinking I can just change out that problem tube, but laziness seems to stop me. (I also do not want to anger the Tube Gods since this tube has given me no problems for many miles. If I make a non-essential change, I'm afraid I will face Karmic retribution.)
Interesting that two tubes would act differently. I have two bikes with high-pressure tubes (a mix of brands), and all require some deflation before filling.
In the interest of science, I'm tempted to push the pump dial beyond the pressure in the tire to see if that would open the valve. Theoretically, if the pump pressure exceeds the tire pressure, the valve should open. I won't try it, though, because something could break in the pump.