I've never done either but I am going to do a HPDE soon at Road Atlanta. My opinion with no backing is that oval racing is harder. I find it harder on simulators for one thing. Everyone says that you only turn left in oval racing so it's easy. Well then why does F1 and open wheel people struggle in Nascar? I'm thinking it's actually harder because the corners are longer. Sometimes a corner might be 1/4 mile long and the slightest mistake gets you overtaken by half the field, where in Road courses the corners are short and if you mess up it's not as big of deal for time lost. Opinions?