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burnthesheep Yes, it is a 2008 HED 3c 19mm rim. Typically, I put a Vittoria EVO CS 20mm tire on it but in the pic she has a 21 mm. I was out of the 20mm and only had a 21 in my stock. I have used a 19 mm on that wheel. FWIW, I think rolling resistance versus aero becomes the trade off and of course handling and safety. So skinny is more aero but depending on the road surface higher Crr. And if the front tire blows, my wife has survived two front wheel tire blow outs at speed, there is not as much rubber with a 19.
I think the 21 mm is a pretty good all around tire on this wheel that offers good handling on a technical course, low rolling resistance, good aero performance and survivability if the tire fails. YMMV