If I remember correctly the US gallon is smaller than the UK gallon, bear this in mind while reading this thread
~ 50mpg Things working against me. Stage 1 mods EJK(more fuel added for performance) I wring it's neck every time I ride. I ride in alot of sand(glide more than roll). Still not bad in my opinion.
I'm getting 76 mpg(UK) which is 64 mpg(US) out of mine. I commute to work on it daily(22 miles each way) im 16 stone and ride it pretty hard through the back roads up to 75 mph max.
Interesting about the preferred octane rating. It states in the '17 manual that it recommends high octane fuel. They did tweak the motor in '17 to up the horses so maybe they upped the compression as well? I will look up the compression in the manual and report back. So many changes in '17... I'm only at 300+ miles and still running the factory motor oil so my mpg is probably low but I seem to be getting around 70 mpg while mostly on the street. Pretty great! EDIT: I was wrong about the 2017 fuel requirements, must have misread that part. '17 manual states "minimum octane rating of 86. Maximum ethanol is 10%. Maximum methanol is 5%." Also the compression ratio did NOT change in '17. (Still 10.7:1) ...But the '17 got a HP bump to 24+ Gotta love it.
I can't speak for 17's (mine is a '16),but here's a link that may give you some help with it (mine is listed on there for 2016's as "Ruby",owned by "Singlespeed92" (of course). Lots of others posting up and keeping track of their mileage,just do a search for CRF250L. Hope it helps http://www.fuelly.com