Oaxaca is a spectacular must-see during your trip through Mexico but eventually you must press on and, when you do, consider Hwy 179 up through the Sierra Nevada mountain range. Leaving Oaxaca, you can opt for the 175 which drives immediately north out of the city and through the same mountains or you can follow Hwy 190 about 40 km southwest to the 179 junction. Opt for the latter as Hwy 179 is decidedly the more meticulous (read: twisty) option. There is a paid variant of the 179 for at least the first stretch to San Juan del Río. I’d recommend sticking to the unpaid route but it’s all the same through the best-worst of it. And thus begins 200 km of two-lane, serpentine mountain highway with endless scenic views and lush vegetation encroaching onto and over the narrow ribbon of tarmac.
Note: You can take the southern route of Hwy 190 all the way to the Guatemalan border. It’s faster, flatter, and thoroughly boring, except where you hit the 50-100 km stretch on either side of La Ventosa. Take this option is you don’t mind sharing the flat, straight highway with 18-wheelers and windsurfing your motorcycle through constant and brutal winds.