This article is from the The Monster Truck FAQ, by Jeff Hawkins with numerous contributions by others.
A. Somewhere in the range of 10,000 lbs. For Racing, the bare minimum
is 10,000 lbs, and most trucks will come across the scales at just
about that weight.
Older trucks from the early 80's weighed nearly 20,000 lbs. and
added weight simply because they would look better crushing cars.
However as time evolved and monster truck racing was introduced,
most started using aluminum to replace steel, tubular chassis and
fiberglass bodies to reduce the weight.
There is a proposal to reduce this minimum weight to 9,500 lbs.
Minimum weight now, according to the MTRA, is 9,500 lbs.
(Courtesy Andrew Palochko).