Would a truck with Load Range C tires run rougher on the road than if it had B Range Tires on it? I don't tow anything so that's not a factor.

 

With my limited knowledge on tires as well as todays tire quality I doubt you can feel any difference. The side wall stiffness and tread design make more difference than anything.

I just put some fairly aggressive tread 18" Mastercraft (Cooper) load range E (10 ply) tires on my 2007 F150 on Saturday. Cannot tell hardly any diff. in driving. They drive smooth with just a small hint of noise at highway speeds. Others may give more insight.