The Silver State Classic Challenge in Nevada (Fastest Rally on a public road)
and the Nevada Open Raod Challenge have strict tire rules...
Copied from 2007 rules: (sorry... the shouting text was in the rules)
XIII. TIRE REGULATIONS
1.
LOAD CARRING CAPACITY: ALL TIRES MUST HAVE AN EQUAL OR GREATER LOAD CARRYING CAPACITY THAN THE ORIGINAL TIRE.
(i.e. The base tire for a 1999 Mustang is a P205/65R15 rated @ 1400 lbs. Any replacement tire must have a load rating of at least 1400 lbs. Regardless of the speed rating or what Division/Class the vehicle is competing.)
Bill
PS: Tires have to have the proper speed rating, <2 years old, 'O' ring lined valve caps, never been fixed... etc...