I don't understand why anyone goes with carbon clincher rims. If your going with carbon, go with tubulars. I'm so happy I did and I'll never look back. I'm going to build a 2nd set of aluminum wheels but they will also be tubulars. Faster flat changes, can ride on them flat, stronger rims, the positives outweight the negatives. Tufo tape is the shiznit and $20 vittoria rally tubulars are great everyday riding tires, those who swear you have to spend $100 on a good tubular tire are full of crap. yes, if you flat, repairing them is a pain but for $20 I'll just throw out the rally's if I flat and if I flat a $100 tubbie I'll send it to www.tirealert.com to have them fix it.

Didn't mean to not answer your original question. Carbon rims are very light IF you go with a low profile. so a 25mm carbon rim can be very light. But most people that go with carbon want their wheels to be aero so they go with 50, 60, or 80+mm depth rims. there is a lot more material to those rims. but if you compare a 40mm carbon rim to a 40mm aluminum rim, ( i think velocity makes one) the carbon rim still wins out in the weight category.