Does Super Saiyan 4 Need a Tail?

So no, you don't need a tail to become a SSJ4.

Why does Super Saiyan 4 have a tail?

Saiyans who lived on Planet Vegeta, like Bardock, Paragus, King Vegeta, Vegeta, Nappa, and Raditz, wear their tail wrapped around their waist in a belt like fashion. This custom is likely to keep their tails from being reached and gripped easily by opponents.

Can a Saiyan go super with a tail?

ALL the saiyans in universe 6 are tail-less, having officially evolved past the need for them, and Cabba manages to go Super Saiyan in a fight against Vegeta. Now for that discussion about possible outliers. Bardock. The only pure-blooded saiyan with a tail we ever see going super saiyan.