I'm not sure if this has been covered before but tires make a big differnce for my 950 Adv S.
When running Conti Trail Attack I get to around 320-330 km before low fuel light (that's my check point) but with more dirtoriented tires, MT21 in this case, I drop down to 250-270km before low fuel light.
I guess that a fast calc that gives approx. from 42mpg (

) to 33mpg (

). In european sense that is from 5,6 l/100km to 7,2 l/100km.
This has been calculated over several highway miles in both cases and are very persitent.
/Zappa