THE C-172M HAD DEPARTED REID-HILLVIEW ARPT (6 MI EAST) & IMPROPERLY ENTERED A RIGHT DOWNWIND FOR RWY 30R AT SAN JOSE. THE C-320B HAD EXECUTED A GO-AROUND FROM RWY 30R DUE TO OTHER TRAFFIC & WAS IN A CLIMBING TURN ALSO ENTERING DOWNWIND FOR RWY 30R. THE C-320B WAS OBSERVED IN A STEEP CLIMBING RIGHT TURN ON A "CROSSWIND" LEG. THE C-172M WAS ROLLING OUT OF A LEFT BANK TURN & WAS AT ABOUT A 15 DEG LEFT BANK WHEN IT WAS OBSERVED TO ROLL INTO ABOUT A 30 DEG IMMEDIATE LEFT BANK & PITCH UP ABOUT 15 DEG JUST PRIOR TO THE COLLISION. THE C-320B INITIALLY ROLLED INTO ABOUT A 30 DEG RIGHT BANKING TURN DURING THE "CROSSWIND" MANEUVER, THEN CONTINUED TO INCREASE BANK TO ABOUT 60 DEG AT THE TIME OF THE COLLISION. ABOUT 1,500 FT OF RWY 30R WAS REMAINING WHEN THE C-320B EXECUTED THE "CROSSWIND" TURN. THE TOWER CONTROLLER DID NOT OBSERVE THE C-320B'S CLIMBING RIGHT TURN, & EXPECTED IT TO EXECUTE A STANDARD GO-AROUND. THE AIRMAN'S INFORMATION MANUAL STATES IF REMAINING IN PATTERN, COMMENCE TURN TO CROSSWIND LEG BEYOND DEPARTURE END OF RWY WITHIN 300 FT OF PATTERN ALTITUDE.