Further to RVF750's post, Convair also built the 880 and 990 with opposite bogie tilts (880 nose up and 990 nose down).
The basic reason for the different angles is as Check Airman wrote in post #2 is to make it fit in the least amount of space. The reason for nose down bogie tilt on some aircraft is this results in the bogie lying parallel to the centreline in the retracted position as the trunnions are skewed so the bottom of the gear moves forward as it retracts. The A380 wing gear is an example and probably the 767. The first step in a 777's retraction is to reposition the bogie to a nose down tilt angle so it lies parallel to the keel in the wheel well.
By mounting the actual leg as far aft in the trunnions as possible and skewing the trunnions you can get a longer landing gear into the same horizontal space. This is how Convair managed to jack up the 990 by 18 inches at the MLG compared to the 880 yet the trunnions are the same distance from the centreline. The MLG alone was 10 inches longer than the 880's with bigger tires but clever geometry enabled it all to fit.
Last edited by CV880; 2nd Nov 2017 at 22:47.