I visited rohtang pass last year in june . june and july is the preffered season for tourist who loves snow.i went there with my friends( college friends) .we did lots of fun together we managed a four wheeler from manali for rohtang pass trek.
When we reached there I cant explain to you it wa s like dream come true I feel like I am in heaven.
It is about 42 km from manali from where you can get car at an affordable price. Very cold whether if you are planning to visit keep warm clothes with your self and dont go much far for treking without guide it can be dangerous for you.