Almost any upright BMW motorcycle can be used for rally. However, you'll probably have a much more enjoyable experience if you have a dual sport model. A GS of any year and displacement is appropriate, as are X series and HP2 enduros. For 2016 we may also run some vintage /5 scramblers! Knobby tires are a must for Sandblast.
Consider any of the following models (including their variations):
G450 X /// G650 X /// F650 GS /// F700 GS /// F800 GS /// R80 GS /// R100 GS /// R1100 GS /// R1150 GS /// R1200 GS /// HP2 Enduro /// Vintage BMW Scrambler