Real world data is very important. The challenge for a lot of devs is how that data is interpreted using the physics and tire model engine in game. What we the users call the handling and feel of the car in game. The problem iRacing has, is that their lead tire model programmer (Dave) is trying to use a physical model (all formula based) vs an empirical model (formula and look up tables) which most other sims use. And unfortunately the physical model, no matter how complex, is lacking in feel and realism because it can't properly simulate what happens to the tires as it breaks traction and starts to slide. Bottom line, not matter how complicated he's made his physical tire model formulas over the years it hasn't passed the sniff test for a lot of us that have had the privledge to driving cars to the limit at race tracks. Cars aren't that hard to drive at the limit in the real world, unlike iRacing portrays. Meanwhile people that drink the coolaid, keep giving iRacing money year after year for a subpar product IMHO. On the other hand look at Kunos. Their sim is also based on real world data, but they understand the importance of feel in the sim. If the data they put into their physics engine doesn't correctly translated to the right feel, they update and modify their physics and tire model engine so that is does feel correct. They don't modify the real world data from telemetry. So the problem isn't if real world data is used but how it's correctly translated into the sim to create the correct feel. Saying real world data isn't needed is a fallacy.