Just put my 40 litres of 91 unleaded inside the tank, for testing ...and bike runs OK altough BMW speciefies RON95 or higher. A very bit lost of low rpm torque, bike not that brightly responsive and valves tend to do a bit more noise (altough it may be just plain wrong feeling too - nothing serious). All works as should be 
Cheers, Margus
Cheers, Margus


. I usually push it hard if i get 500km, on smooth touring often mode more than 600kms. Nice functional piece of plastic w/o affecting any bike's dynamics - driving feels the same as with stock tank, just you hold about twice the fuel.