There is about a gallon left when the F-trip comes on, so if you are careful you can get around 40 miles. I normally get around 100-120 miles until it comes on, depending on how I am riding.
On a tour I brim the tank, that means on the centre stand fill it to the neck, then slowly dripping another litre in as it fills the air pocket.
I once got just over 150 motorway miles before finding a petrol station, but was panicking and nursing it the last 20 miles. I managed to get 16.5 litres in so there can't have been much more than a litre left in the tank.
On a tour I brim the tank, that means on the centre stand fill it to the neck, then slowly dripping another litre in as it fills the air pocket.
I once got just over 150 motorway miles before finding a petrol station, but was panicking and nursing it the last 20 miles. I managed to get 16.5 litres in so there can't have been much more than a litre left in the tank.