You can start or end at either city, as both are good motorcycle destinations. Start in New Glarus, Wis., which is 25 southwest of Madison. Proceed west on state route 39. Stay on Route 39 for 31.1 miles to Mineral Point, Wis.
This route along Route 39 features some of the most bucolic farm scenery in Wisconsin. The driftless region of southwestern Wisconsin represents a geological area where the glaciers didn't scrape the terrain flat. So the entire ride includes both high vistas and low creek bed valleys. You'll probably see vehicles stopped along the roadside, taking pictures. Anytime during the summer is fine, when farmers are doing their work (be mindful of farm machinery) and the fall provides some excellent fall colors as well.
There might be some bumps as you exit or enter a couple of the towns, but other wise Route 39 has been recently repaved along this 31-mile section. Smooth ride as of Labor Day Weekend 2017.
Both the starting and ending cities, New Glarus and Mineral Point, are popular Wisconsin tourist destinations, with very pleasant and local restaurants and bars. New Glarus is also the site for New Glarus Brewery, home of Spotted Cow and other Wisconsin-only beer flavors.
Motorcycle Road Additional info
You can also take any (or all) of the local county highways that jut off from Route 39 during your ride. Each will take you on a variety of rolling hills and tight curves. Most are in decent shape. Just be mindful of farm machinery and Amish, horse-drawn buggies.