Drag racing
The National Hot Rod Association (NHRA) oversees most of drag racing events in North America. The next largest organization, Feld Entertainment's International Hot Rod Association (IHRA), is about one-third the size of NHRA. Nearly all drag strips are associated with one sanctioning body or the other. The NHRA is more popular with large, 1/4-mile, nationally recognized, tracks., The IHRA is a favorite of smaller 1/8-mile local tracks (and offers selected races on their national tour under the 1/8-mile format). One reason for this is the IHRA is less restrictive in its rules, such as rules on nitrous oxide (legal in Pro Modified) and oversized engines.