creature advancement and speed

[brun]

I'm still looking for it, but I can't seem to find anything that covers speed when advancing a creature. I understand it might be touchy or a case-by-case thing but are there any guidelines?

 

[Epametheus]

Dragons change speed as they increase in age categories.

As far as I can tell, nothing else does.

So as a general rule, speed doesn't change as a creature gets more hit dice.

 

[brun]

But when a creature gets 2 size category larger, isn't it logical it would become faster? With longer legs, the speed would increase. This is the same logic for the lower speed of small caracters.