Since you won Senior C previously, you'd be a B category rider. Obviously, the displacement classes and appropriate age classes are available to you based on your category (i.e., Senior B, 250B, etc.). In addition, the open short course class Sportsman is available to anyone not wanting to ride the long course.
If you feel you're no longer qualified to ride the long course, you will have to send a written request to the circuit president stating your case. The board will have to approve any downward movement (i.e., back to C category).
The complete TSCEC rule book including class definitions is available from:
http://www.tscec.org/rules.htm
Section 6 goes into great detail regarding the Classification of Participants and section 7 lists all the classes.
Ongoing discussions regarding the TSCEC are generally place in the TSCEC forum below.
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