Praise be to Allaah.
If this is based on the condition that one of the partners in this scheme can buy one of the group’s cars, then this is not permissible, because this comes under the heading of “two transactions in one”, since it involves partnership (being a partner in the scheme) and purchasing (buying the car). But if this is not a condition that was previously laid down, then there is nothing wrong with it.
And Allaah is the source of strength. May Allaah bless our Prophet Muhammad and his family and companions, and grant them peace.