Here's a route I suggested on a recent thread:
If you have the time, here's a route that hits three favorite paved moto roads in Texas: http://goo.gl/maps/Mrr03
1. Texas 118 from IH-10 at Kent to Fort Davis.
2. River Road (FM 170) from Presidio to Big Bend Nation Park
3. Ranch Road 337 from Camp Wood to Medina.
It keeps you out of some of the San Antonio congestion...
Short cuts would be to delete #2 by riding direct from Fort Davis to Marathon or deleting #3 by riding Hwy 90 straight east from Uvalde through Castroville and on through San Antonio to link with IH-10.