I understand why larger router bits should be operated at lower speeds and there are a multitude of router bit speed charts out there to help you choose the correct speed for any given bit.
It all revolves around (haha, see what I did there?) the rim speed of the bit and, from what I've been able to work out, it looks like most recommended rotational speeds equate to a rim speed of something between 100 km/h (60 mph) and 180 km/h (110 mph).
But then every article you read about this will state that the size of the bit is only one of the factors to determine the speed at which you want to run the router. Another important factor is the hardness of the wood. But, while every article gives you a chart to illustrate how bit size affects the speed, I have yet to see something illustrating how hardness of the wood affects the speed.
Yes, I get it, harder wood = slower speed, but how much? If the bit size speed chart tells me that the max speed for a bit is 20,000 RPM for instance, I'm presuming that is if you're cutting a soft pine. But if you're cutting African Blackwood or Ipe, you should use a slower speed but how much slower?
Any rules of thumb or charts for this perhaps?