I like to use rubber grease when I change the tire and tube on my dirt bike.
Rubber grease is by no means necessary when installing the tube and tire on your dirt bike, but it does have many benefits.
Rubber grease makes installing your tire extremely easy, and it fills every tiny crack in the rim and tire to seal it from outside contaminants.
Related: Do you know how the rim lock works on your dirt bike rim?
If you want to give rubber grease a try, you can get some on eBay.