Typically – if your one modification moves you from Sport to Tuner – it’s because it’s not a simple bolt-on part. It means more adjustment or more complication in how to handle that modification or system, and more well, tuning. If your “one modification” puts you in Max, then chances are that modification opened a rabbit hole of fundamentally changing the car. Maybe it is changing suspension geometry or doing internal engine work which can have all kinds of repercussions or gains, depending on how far you went. Essentially, if the modification opened massive window to the amount of change, it’s a Max-class car. If you find yourself in Unlimited – it’s because the things you have done are probably not within the parameters of what is considered a “Street” car.