The Crawler Innovations Lil Nova 4.0 1.9" Class 1 Crawler Foam was developed for SORCCA competition using Class 1 tires ranging in height from 4.19" and smaller. This foam was designed to not over stuff the class 1 tires the way the 4.25" Lil Nova does. The 4.0" Lil Nova was designed for 6 pound and lighter weight rc vehicles, focused on scale rc crawling performance. If you have a heavy rig and need more support from your class 1 tire, the 4.25" Lil Nova is better suited for that.
These inserts feature a standard inner foam, with a medium density outer foam. The closed cell inner foam fits .750" wide bead locks, is super dense, water proof, is not temperature sensitive and is extremely durable. The conventional outer foam is not temperature sensitive, but it is not water proof.
Typically, you want to use a firmer foam in the rear than what you use in the front. This will help to prevent the truck from lifting the front end when climbing obstacles or steep grades. Additionally, the heavier the truck, the firmer insert you will want to use. Package includes two foams. Foams are also available in soft (CWR-2091) and firm (CWR-2093) densities.