No. Slicks were not used until the early '70s. If you look closely at the premium classic race cars, you will notice that none of them have slicks, even though they have RH tires. This shows that PD attempted to model the old racing tires these cars had, but the physics are still messed up. Yes, they don't have as much grip as most of the other race cars with RH tires, but there is still too much grip. After driving the Ford mark IV on RH I can confirm that the car is very tricky to control, but the grip that exists before the car loses control and spins out is quite exaggerated. That said, the car, although it has more understeer on SS, is much more predictable than with RH. The most grip-accurate tires are SH, however the WSC uses SS because Furi apparently cannot drive the Ford Mark IV on SH without spinning out everywhere.