There are a several ways to do this ride. One is over Swan Mountain Road both ways, another is down to Frisco, across Dillon Dam and then up Keystone, and of course one way around the lake and the other over Swan Mtn. The route shown goes around the lake to Frisco, Dillon & Keystone and then back over Swan Mtn to complete the loop around the lake.
This is my preferred direction over Swan Mountain since you are climbing on a bike path and then descending from Sapphire Point to Summit High School on the road where it's not difficult to keep up with the light traffic.
Climbing over Swan Mountain Road both ways is shorter (30 miles), but adds some climbing since you are going over Swan Mountain both ways.
The route shown uses the roads in Keystone to the River Run Base Area rather than the bike path, which is in poor repair, narrow and has a number of blind corners.