The dust in this board track film

Thanks for the vid link. Did you notice how people watching were dressed? Suits and ties?

Dust kicking up from the bikes I don't know about that, my guess is the exhaust smoke coming from running to rich or just oil dripping down onto the exhaust pipes & motor.

It does not take long to race 10 miles at 100 mph.

Peace Crazy Horse.

That was not dust that was being kicked up as Crazy Horse said, it was oil coming out of the exhaust.
A lot of the early bikes it seems, had hand oil pumps so the rider could pressureize the oil tank and force oil into the engine to lubricate it. The oil landed on the track and soaked into the wood.

I've mentioned this before but I had a book written by a board track racer just before the second world war. He had a a photo of himself with no shirt on and it looked as if he had lost the worst sword fight of his life, He was crisscrossed with scars from the slivers that they had to remove from him when he went down onto the track. Must have happened more than once. He told his story about starting on his own and then racing with different teams and what it was like to lose people he knew. I lost the book in a house fire.

Read another story about the boardtracks toward the end of the era where the tracks were wearing out and they still raced on them.

All the racers noticed that there was some thing on the track ahead and it was moving like a bag blowing in the wind but when they got there it was gone. Took a few laps to realize that it was kids sticking thier heads up through holes in the track floor and watching until the bikes got close and then ducking down until they were past them. At a 100mph what would hitting the hole do to bike and rider. They shut the track down not long after that and built houses on the land.

Steve.