In the course of many visits to all parts of Kruger, I have never travelled on a dirt road in KNP that posed any danger to my (personal or hired) car.

For the most part the roads are superbly maintained. Sure some may be corrugated, but that isn't going to cause any damage unless you refuse to adjust your speed. But any road that is unsafe will be closed off until it is repaired - the Parks people are far more inclined to be overly cautious than cavalier about safety.

The dirt roads are much more fun too: you feel so much more part of the bush than you do on a much busier tarred road. We actively choose the dirt roads in most instances. But I don't mind if others stick to the tar: just makes the dirt roads quieter and more special.