Forgive me, but after a look through the forum I did not see much of anything on motorcycling racing in the USA during the early 20th Century. I am sure that there might be something in here somewhere, but various searches failed to find it.
Although my primary research focus for some years has been motor sport contests in the USA during its first quarter-century, basically 1895 to 1920, in recent years I have started to take more and more notice of the motorcycle racing taking place, especially given that it is, of course, motor sport. There is considerable overlap in venues, for instance, and the AAA and the FAM both seem to have done little good to the blood pressures of all concerned when it came to racing.
I realize that this is probably something that does not attract much interest (if nay) here, but other than a few (with the accent on few...) Web sites and what I have managed to dredge up from the various periodicals from the era (Motorcycle Illustrated, for example, of which only a pathetic few copies from this era have been digitized) not finding all that much. What I am finding is certainly interesting and often fascinating, but needles and haystacks seems to apply, as ever.
Much of it must be out there somewhere, only problem seems to be finding it!