The (24 mm exterior width / 19 mm interior width - my measurement) Dyads will easily fit 28's. You can try 25's, but I wouldn't advise it on rough roads. See http://www.sheldonbrown.com/tire-sizing.html (near bottom of page) and http://www.schwalbetires.com/tech_in...dimensions#rim (also at the bottom of the page).

I ride my 26 lb Americano unloaded on asphalt with 30-622 Marathon Racers . Although I average about 15 mph on Pacific Coast Highway in northern San Diego County, I am smoked by nearly everyone with drop bars. So I tell myself I'm in it for the fitness, not for racing.

The CDMBR was really one of the best parts of the trip. Unfortunately, I didn't have the new map that routes through the Flathead Wilderness, so was on too much asphalt.