How often do teams build a new car?

Teams are always building new cars and updating existing ones. Things change fast and the cars are in a state of constant evolution. The main cost savings comes from being able to use the same chassis at so many different tracks if you choose to. With the old car you had different chassis that worked well at only a few tracks. The fabricators had a ton of work to do with the bodies being fabricated differently for high downforce or low downforce tracks. Now all the bodies are basically the same. Remember when RCR sucked and wasn't running well? They went back and redesigned the front suspension and now they are back on their game. You're right. For the most part, what works today won't work tomorrow.