Jenny, I was wondering the same thing since the valve has what looks like a slot in it. But I tried that and rotating it doesn't appear to do anything.
I was thinking of these inflatable tires as BETTER than that solid tires, but maybe that's not the case. (By the way, eventually, it might be cool to replace the tires with balloon-type bush tires.) These have a 4.5 inch diameter.
I found this thread on inflatable tires. Seems that others have had similar problems:
http://www.rcuniverse.com/forum/begi...what-pump.html