There are numerous possibilities, and no one FKT route has yet become standard. Here is some of the discussion that happened on our old website:
Tim Seaver (7/11/2014):
Mount Mansfield, Sunset Ridge/Maple Ridge Loop w/summit (VT)
I've been running this loop for almost 20 years, and still think it's one of the finest in New England.
The route: It starts and finishes in Underhill State Park at the trailhead map board at the top of the parking area, which approaches the Sunset Ridge Trail via the CCC road that has a short cut route called the Eagle's Cut that most people use rather than walking the road. In one mile, the CCC road bears right ( where you will be running out at the end of the loop) - the Sunset Ridge Trail starts here on the left. Where the trail intersects the Long Trail at the ridgeline, turn left to take the short out and back to the summit. Returning to this point, continue south on the LT. This part is a blast. Cruise as fast as you can across the ridge, ending up on a service road - look for the LT exiting right down a steep cut ( well signed). Stay on the LT to the Maple Ridge Trail, then hop on the CCC road ( go right) for a short uphill grind followed by a great fast finish over mossy roads and finally the CCC road.
Today I did the loop (with the summit spur out-and-back) in 1:43:07 , which isn't my fastest time ( around 1:38), but the first time I carried a GPS.
It's about 9 miles and 3000' of gain. I was at the summit in 49:07. I'm not sure why the GPS track says 7 miles, it was just a cell phone app.
It's a grunt up to the summit, but from there the rest of the run across the ridge line and then down Maple Ridge is just plain fun - lots of open fast terrain and fun little "problems".
Kind of similar to the Falling Waters/Bridle Path Loop, but smoother and faster.
I've been trying to get my trail running friends from NH to come over and check this loop out, but all I hear are excuses. Maybe if an FKT is involved they will have a change of heart.
On 2/7/16 I ran Sunset Ridge (from the proper trailhead) to the summit and back in 1:05 w/ a 3min summit break to snap a photo for a couple. Heavy Salomon Snowcross and microspikes through a couple inches of fresh powder below treeline and spotty deep stuff above.
I'm pretty sure Eric Blake has the FKT up the toll road - 31 ish minutes. Nasty!
Take a look at strava - will give you a loose idea although many FKTs are not on there.
I think most of the actual FKTs on mansfield (various routes) will be way sub 50 minutes. It's only 2500 ft of gain or less depending on the trail.
Should the Sunset Ridge trail from the Mountain Road be considered the FKT starting point? www.vtstateparks.com/pdfs/underhilltrails.pdf
Just gotta have different FKTs for different routes. For there are quite a few fun ones. Just went up hellbrook, over the adams apple trail, and then up the LT to the chin today in 48:07. This can be very easily improved upon I'm sure.
Tim Seaver (8/4/2016):
Here's another fun route that doesn't see much activity: Up Sunset Ridge to the LT, tag the summit, then back down the ridgeline (LT) to the Maple Ridge Trail, down to the CCC road and back to the TH.
Ross Henry (4/24/2017):
Went up the Sunset ridge to the chin from the Underhill State Park. From the Trailhead start I did it in: 35:55. The Ascent from the first kiosk of the parking lot I did in: 44:25. Definitely can be improved upon!
Conditions were still fairly snowy and wet, so traction was pretty rough even with trail shoes. There doesn't seem to be anything definitive about what the FKT is. Tried to find it on strava as well as other links here, but there doesn't seem to be much written about the Mansfield FKT. So I think this is it? At least for Sunset ridge.
Would love to see some serious goes at it!