If LFS, there's a certain level of idealism with regards to the physics that you have to understand. The ideal is, if the physics work right for one car but not for another that , then the physics are wrong. If there's something odd about the way a vehicle handles or performs, you tweak the vehicle's design, not the underlying physics of the vehicle. If you need to tweak a vehicle's design using unrealistic values to achieve the desired result, then the physics are wrong.
If I understand correctly, rFactor is much the opposite. Each car has its own subset of physics and design properties. If something is wrong with the way a car handles, just tweak its various properties until you get the desired result, regardless of how well the design matches up with reality.
LFS tries to make everything right, even if it may feel off sometimes. rFactor tries to make everything feel right, even when it's not truly right.