Sorry, I saw the thread title but I don't use numbers :). The route from Linares, Iturbide, Galeana, to San Roberto is one of the most beautiful drives in northern Mexico. Takes about 1.5 hours, is windy and scenic. Lots of places to pull off and have a stop and go through some small towns. Galeana is famous for the Pozo de Gavilan (cenote) and the Laguna del Labrador (crystal clear). We have stayed out there before boondocking. I would check Google Earth for clearance into Galeana if you have a big rig.
After Galeana your in pines and it levels off before starting the descent to San Robert.
Laguna del Labrador (parking and palapas)

Excellent highway and new bridges (previously destroyed by Hurricane Emily)

If you were to come from Reynosa you can go around Monterrey by taking the Cadereyta to Allende, NL highway (Hwy9), Hwy 85 south to Linares and turn right. At the 85 and Linares intersection as you turn right on the left side is a huge gated city park called La Nogalera and you can stay the night there. Secure and guarded. For more info you can PM me.
Great route if you like mountains.