@Kavita Batra Welcome! The Model S is a very mature vehicle known to have few problems in current production.
The Model X is a new model that has experienced problems in the early production models. The current Model X production models are reporting few problems and it appears that Tesla has made improvements.
You should not worry about the Model S having things go wrong. You are in the Model X forum (look at top of page, find the house, click on tesla motors forum and select the model S forum) and would be better helped by Members in the Model S forum to answer your question about driving on uneven roads. Where does your friend get their info? do they own an S? Better to get info from current members on the S forum.. look at threads for topic that may be close to your question. Good luck and congratulations on your Tesla purchase... you made a great choice.