As someone who has a diverse appreciation of motorsport I often find myself explaining the difference between series to non-fans or those that are fans of only one. Over time I developed a simple metaphor based on something everyone understands. Soda (or pop for those linguistically challenged).
Imagine you're at the grocery store and you enter the soda isle. It's visually overwhelming in its bright colors and varying brands that differ slightly on the chemistry level but greatly in taste and followership.
F1 Classic is the racing by which all others are measured. So Classic F1 therefore receives for comparison purposes the soda brand by which all others are compared = Coca-Cola Classic (With Sugar) Once you try it you will love it.
On this scale I rank other series as follows:
New F1 = Coca-Cola Zero; Similar to the original just lacking a key ingredient.
GP2 = Diet Coke; An empty version of the original.
Formula E = Decaffeinated Diet Coke; Entirely without purpose.
IndyCar = Pepsi; Just as good as its competition just not as popular.
Indy Lights = Auqafina; Flat and flavorless.
NHRA = Mountain Dew; High Energy, but not for everyone.
Tudor/IMSA = Dr. Pepper; An excellent beverage that you have to try in order to decide for yourself. You'll either love it, not love it, or be completely indifferent.
WRC = Squirt; Zesty, exciting and yummy; but most people have never experienced it.
I've struggled a bit to find a place for the NASCAR brands, because to me, though it is racing it's on its own level. I came to the conclusion that NASCAR is the Stewart Soda brand. Old-school charm and available in varying flavors its followers are aggressively faithful and vehemently opposed to change.
So that's the Racing/Soda scale. What favorite series of yours did I miss and what soda do you think it represents?