Fuel tank mod?

[darrsi]

I have always averaged about 10 miles per litre (45mpg) on my FZS600, ST1100 and CBF1000 with mixed riding. My FZR1000 was (quite) a bit thirstier.
Comuting on the FZS600 into London from Sussex averaged about 50mpg

Same as, I've always used 10 miles per litre as a decent gauge, obviously give or take, but i'm always riding in unavoidable traffic, so i expect to use more than a fluent motorway run for example where I'm moving at a constant pace.
Not even worth me doing the Fuelly thing because my journeys are not a true example of fuel usage that the bike is actually capable of.