This is some funky English. You cannot drive rally, makes no sense. The best way would be to say "why do you want to race" or "auto race" or at least "to rally drive"/"drive in a rally". Although the word "rally" isn't the best option to describe car racing, as it has very different meaning that are used more frequently.
It would need to be “ajaa rallissa”, first of all. But my understanding is the meaning is kind of different, here it means doing this as a hobby, type of driving, and “ajaa rallissa” seems to mean participating in a race. For example: “ Hän ajaa Rovaniemen rallissa”. I’m not a native speaker, so the explanation can be not great, however, the spelling is something that you got wrong there for sure.