This article is from the The Monster Truck FAQ, by Jeff Hawkins with numerous contributions by others.
A. Yes, Pro-Stock Class. a smaller tire class:
Sam Marino debuted the Raptor and the Pro Stock monster truck class in
June 1997 at the Truck Fest in Charlotte, N. C. Featuring 48" tires
in place of the more familiar 66" tires, the class was developed to allow
more participant growth in the sport. Running a Pro Stock class provides
a cheaper, more realistic method of competing while still keeping the
enthusiasm and principle of full blown monster truck racing.
Currently Sam is exhibitioning up and down the eastern seaboard hoping to
add this additional class to monster truck racing. (Info courtesy Andrew