They are created for each individual track & distance.

It takes the best times recorded then one goes from there .

There is a speed thingo I believe in racingandsports.

It is questionable how good they are.

I guess there is an art in how they are used.

Google Beyer Speed ratings.

When he was in Australia many years ago , he could not make his format work as well as he could on his home tracks in the USA.
He was considered the be a master of speed ratings.

Cheers.

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Cheers.