When the spies returned from scouting the land and gave their report of mighty opponents, 13:30 tells us that Caleb silenced the crowd and argued for going into the land, and then 13:31 says "the men who went with him" argued otherwise. It is only after the people begin to rebel that Yehoshua joins Caleb in speaking in favor of going into the land (14:6-7).
Why didn't Yehoshua speak up earlier? Was he not initially convinced (it was 11 to 1) but he changed his mind? Or did his opinion not change but for some reason he left Caleb to handle it, even when it wasn't working?
Rashi has nothing to say on this, and I didn't find anything else in scans of (incomplete) chumash commentary.