I did the FR172-650 loop today and can report 172 is in very good shape but 650 is not the best.
First, Hewitt Road has been grade so that part is very good, although there are a few large puddles. Turning off Hewitt Road onto FR172 there is sitting water about 10' across in the wash but only 3-4" deep and the ground under it is very stable so no issues with a normal clearance vehicle. From Hewitt Road to the 172A intersection (to Woodbury TH) the road appears to have been graded in some sections and is easily passable with anything with just a tad extra clearance (like a Subaru). There are a number of puddles along the way but most are just a nuisance to splash through.
After the 172-172A junction it gets a bit rougher and there are a few ruts here and there but nothing that would stop even a 2WD vehicle. From the 172/650 intersection to Roger's Trough there are ice-covered puddles but nothing of any concern.
Now, FR650 is a different matter. It has plenty of ruts, is very rough, had many muddy spots, but the worst is the ice across the road on all the north slopes and many of the others. The problem is snow that melted and ran across the road then froze, which makes for some treacherous conditions. An ATV ahead of me almost slid off the inside of a turn. It was banked pretty good and he tried to stay high but slid sideways, then gave it too much gas just spinning the wheels, which made it worse but he got it stopped just in time. Kind of counter-intuitive for the guy, but the problems was cause because he was going too SLOW. If he kept his speed around the corner he would have been fine, which is what it was like for me.
So in short, if I still had my old 2WD Toyota Tacoma pickup I wouldn't hesitate to drive it up FR172. But for FR650, even going down, I'd recommend a decent clearance 4WD SUV or pickup.