Last Feb we rode through Tuxtla Gutiérrez to San Cristóbal de las Casas where we overnighted. Then took Carretera Federal 190 to the border, passing through Comitán and Ciudad Cuautehmoc to make the Guate crossing at La Mesía (La Mesilla). SC de las C is a nice town to overnight in and 190 provided a pleasant ride to a friendly crossing at La Mesilla. From there you simply take CA1 to your turn off for SJC. It's a pretty sweet ride. Don't know what you're riding or how you feel about dirt roads but there is one paved road into SJC off of CA1 you can get onto from Zaragoza which lies due south of SJC and just west of Chimaltenango. Looks like a nice piece of road on Google Earth. If you have time on your return consider heading east through Guate City then north to Tikal for the ruins. Then Palenque on your return through México. You might even see Ester there. Do try to meet up with MikeMike in Veracruz if it works out that you overnight there. He's someone worth meeting and certainly worth riding with.