"It’s do-able as a C route, as long as the write-up is clear about the degree of difficulty. It’s a bit more vertical than would normally be in a C route, The leaders would also have to be very precise about pacing – doing a true 14 on flat terrain but not letting people blow themselves out early on the climb – it’s essentially a 14 mile climb with very little let-up. C riders would need low gears to do this because of the length of the climb – most don’t have the same stamina as A or B riders. So it can be done, but the leaders have to monitor the pace and not let folks get too enthusiastic early in the climb, so they can make it back to the train station." Carol Waaser
The carriage roads are gravel. You will need at least a 25 m tire. If you have a mtn bike, so much the better, but you will go slower on the roads to and from. They are not steep and there is room to pass. The views are majestic. On a clear day you can see High Point, NJ, the Storm King/Breakneck Ridge gap of the Hudson, the high Catskills, Sam's Point, and Skytop, Mohonk.
You will need to get an early start and leave yourself time to get back to Poughkeepsie. But most of the way back to New Paltz is downhill. You climb out of New Paltz and it is fairly flat on 299 from there to New Paltz Rd, with a good shoulder. The rail trail back is down hill.
On the plus side, you can forgo the carriage trail to Minnewaska from "the Trapps" and just stay on 44/55 to the state park, climbing the auto access road instead of the carriage roads up to the upper parking lot. You can take a detour to see the Awosting Falls.
On the negative side, 299 from New Paltz does not have a great shoulder. But just stay as far to the right as you can. That's what everyone else does.
I strongly advise you to have a copy of a map of Minnewaska State Park, although there are posted maps on signs along the carriage roads.
For a C rider, this will be some adventure.