Board Thread:Suggestions forum/@comment-26897694-20170514062945/@comment-27509628-20170518074629

Also, I can't quote directly, but in "The History of Middle-earth, Vol. 2: The Book of Lost Tales Part Two, III: "The Fall of Gondolin"" it is stated that Balrogs are only twice the height of elves (source). Even if Smaug was only 25 meters long, they would still be able to ride on him. And, Smaug was smaller than the big dragons from the first era. It's not canon, but I think this is the most accurate: