[сандро]

Cause you cant change every values and friction between steel and steel is a constant value of nature (~ 0.1431 ), I recommend to keep these values as given
I suggest to set the values a bit higher for engines with more than two cylinders (not articulated ones), for instance compound engines, in mind the characteristic oscillation of the traction forces is not so bad as in engines with two cylinders.

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Velocity dependent friction values. Used for mimicking internal friction and drag.
The values here allow friction calculation to change over two velocity segments

(shortened.
Look for Joe’s tool and Add On, who describes precisely the matter