I have learned something since my original post. I "thought"
board track motorcycle racing was Indoors...like bicycle racing..roller derby...etc.
Totally NOT SO.
Board Track Motorcycle racing was like..
.Daytona Beach..The track was over a mile in length....ALL 2x4 boards layed on edge....outdoors, and banked....except instead of asphalt as today..they had boards.
If you think about it..this is 1910..1920. There are no
Paved roads...never mind paved racetracks. So they used boards to..."surface" the tracks. Better than dirt. This explains the 100 MPH speeds they achieved.

NB
For those interested: Go to
U-Tube and plug in "Board Track Motorcycle Racing"...or something like that..It will come up.