i ride a rigid single speed. and i have 30 mm id carbon rims on it. the ride is nice. of course, if i take this bike to technical rocky places, the ride is jarring. but i doubt this has to do with the carbon rims. it is a rigid. it has got to be harsh on specific terrain.
as others have said, put a wide 2.4+ tire on it and you'll be grinning all the way.
