Instead of following CO 9 from Silverthorne to Kremmling, I'd suggest turning off CO 9 onto Ute Pass Rd, crossing Ute Pass, and following Grand County Rd 3 north, joining US 40 around Parshall. Much prettier and probably safer than CO 9, which has gotten awfully busy in the last few years. Most of GCR 3 is paved, the unpaved part is very well graded. I'm not sure if it would be faster or slower than following CO 9 into Kremmling, it's fewer miles but more climbing. I've seen some USFS campgrounds along GCR 3 that look very pleasant.
If you've got really low gears and you're feeling really strong and adventurous, why not try Old Fall River Road in RMNP? It's well graded dirt, but pretty steep in spots (10% + as I recall). It joins Trail Ridge Road east of the high point of that road, so you could continue across RMNP on Trail Ridge Rd. I went up Fall River Road and back down Trail Ridge Road earlier this summer, it was a really pretty ride. It would be a real challenge with camping gear, though.