A passenger car can make it down Shnebly...If you're insane...I mean 
adventurous!
I actually took my del Sol down it a couple years ago.  This was before 
I put the racing suspension on (now I barely make it over speed 
bumps)...and I did it on a dare:)  Had a friend with his head out 
spotting the "oilpan crushing rocks."  The Pink Jeep people gave us all 
sorts of crazy looks:)
But I often see rental cars going up and down it.

Yes, I would call ahead and see if it is closed yet for the winter.  
Kev and I often take the dogs camping off Schnebly about 5 miles from 
I-17.

Someday we will have the proper vehicle to drive down that road!
Team desertSol
Chelby & Kevin
+
Kiva and Lancer (German Shepherds)
Apache Junction, AZ
www.desertsol.com/~chelby/geocaching