Having decided on the route, the next task was to try and determine the best month to start.  Having set a target of 2,000kms/month - I then looked at the weather at 17 locations between Cartagena and Cohaique.  Typical Max and Min temperature and monthly rain fall was all put into a spreadsheet.  Then an average of the 5 month journey was calculated.  The best month to leave Cartagena is July - this should give us an average temperature throughout the trip of 21 degrees and an average rainfall of 0.58inches

The other key criteria was to pass through the Bolivian Salt plains before the rains start at mid to end of October, arrive in Southern Chile in the summer (warmest and driest) and pass through Equador in the least wet time of the year.  A start date of 1st July met all these criteria...