Crash the car in practice, that should load all the extra bits into the cache. Going back to the F1 2k days, we used to use the first practice lap and continually look around as you drove the lap. This stores as many of the enviroment textures as possible, also explore the edges of the track to load all the various sounds for curbing, sand, grass etc. Stuff the cache with as many trackside objects and sounds as possible.