If paved with asphalt, this would be a great, scenic trail. Unfortunately there is a crushed asphalt, gravel surface not suitable for road bikes, recumbents or anything without fat tires.

Road bike (15mph) from Jackson Landing to Stanton. Trail in good condition with some cracks at regular intervals. Leaves covering some of those cracks made it interesting at times. Peaceful setting.

I biked the entirety of the improved portion of this trail yesterday 10/9/19.
I started in Ovid, where there was parking by the trail but no public restrooms and headed west. As anticipated, the trail was improved and very nice until Smith Road just west of Owasso (about 7.5 miles). Past Smith Road, the trail was overgrown with grass 2-3 ft tall and trees growing across--impassable without a machete. I turned around there and rode all the way through Saranac, where the trail ended at mile marker 133. Past there, the trail had original railroad ballast with large stones, not passable even with a mountain bike. I then turned back and returned to my car in Ovid. The most beautiful part of the trail was West of Pewamo, as it was along the Grand River valley. East of Pewamo to Owasso, it is primarily farm land sheltered by a line of trees in most places. There is parking and restrooms along the trail in St. Johns, Fowler, Pewamo, Muir, Ionia and Saranac. The trail was beautifully, newly paved asphalt within all of the towns, and hard-packed crushed limestone in between. It was perfect for a cyclocross bike or mountain bike and most likely entirely passable with a road bike (some rare soft spots in the crushed stone could be difficult). I will definitely ride this again. 51.5 miles of improved trail total, for a round tip distance of 103 miles.

We parked at the Trailhead just South of Cadillac. Biked 2 miles into the city of Cadillac for lunch. There's also some great little shops in Cadillac.
Biked from Cadillac to LeRoy and back, approx 35 miles round trip.
Trail is very nicely paved asphalt through open areas and wooded areas.
Great ride on the Northern section of the trail.
Between Cadillac and LeRoy you will pass through Tustin which has a few small stores if you need anything.
Along the trail there are wooded sections of huge white pine trees.

We parked at the Jackson's Landing Trailhead in Greenville. Biked a few miles North on the Heartland Trail. This was after we biked on the Flat River Trail.
The Heartland Trail is newly paved and in very good condtion.
In Greenville there are places to eat and other services.
Hope to do more of this trail in the future.

We parked at Jackson's Landing trailhead. Large paved lot and portable restroom.
Trail is asphalt paved and plastic decking. The plastic decking sections are extensive and very rough and bouncy if traveling at a decent speed.
The trail goes along the Flat River. Coming out of Greenville the trail is more of a paved sidewalk, up near the High School.
Trail services include eateries nearby since most of this trail is within the city limits.
You can also access the Heartland Trail from Jackson's Landing trailhead.

Biked the trail from Middleville south on a cool clear weekday in late September. Trail was not crowded but a bit bumpy in a few spots. We also biked the new portion a mile long and it was beautiful. Nice restaurants in town near the trai.

We arrived late in the day just as storm clouds were rolling in, but we managed a ride to Riverdale and returned to Alma just after sunset (17.5 miles). The trail appeared to have been recently re-sealed and, except for a 100 yard section west of Warner Road, it was buttery smooth. The only hazards encountered were the numerous bunnies running across the trail in front of us.

Planned and completed the entire trail starting from Grand Rapids Comstock Park to downtown Cadillac and back, last weekend. Was riding a gravel bike and can say that the gravel sections including the paved were so much fun to ride on. That being said, there are some deeper gravel and sand sections, mainly in the smaller cities at the crosswalks, so beware. Not bad, but you’d want to keep your eyes out for it. A fair amount of restroom stops, if you plan them. Highly recommend stopping in Rockford for a brew. Abundant campgrounds in Cadillac. Very much a friend and family group area though, so a little clustered. Stayed the second night at the Young’s Lake Campground and I could not recommend more! Very friendly owners greet you at the front and it’s not too big. It has its own little beach right in front of a lake. Some winding roads to get there, but super worth it. The stars were amazing. Great trail throughout, but when they do get to paving the entire trail, I’m sure it’d make the distance a lot easier and more accessible (although I personally liked the silence with no one else around but nature) FYI saw some Blue Racer snakes on the trail near Cadillac. Nonpoisonous, but you’ll be surprised. Recommend friendsofthewhitepinetrail.com for more details along the trail.