The problem is that the grid of the maps breaks right there.
If you are coming south on Mex 57 take the north or south periferico around San Luis Potosí and pick up the combination of Mex 70 & Mex 80 heading Southwest to Ojueles de Jalisco. If I remember rightly 57D is a cuota bypass that rejoins 57 south of the city and is the fastest route to Mexico. DO NOT take that bypass although it may have an exit for Aguascalientes. It should have but I doubt it.
You pick up the combination of Mex 70 & 80 almost directly across the city from where you enter the periferico on the Northeast. DO NOT continue on Mex 57 south which you will see from the map is almost 90* to the left and shoots off Southeasterly to Querétaro.
At Ojuelos continue Northwesterly on Mex 70 to Matancillas and then westerly on Mex 70 the 87 km-54 miles to Aguascalientes.
I haven't driven this route but this is what my maps show as the direct and principal route. At Aguascalientes the signage to San Luis Potosí is very good. I would expect the same at Lan Luis Potosí since Mex 70 is a principal trucking route.
At Aguascalientes look for the Airport, Mexico, Lagos de Moreno signs and follow them to the cuota to Guadalajara. The exit is well marked but not much in advance and it's busy. . On the cuota do Not miss the Guadalajara exit (about 10 minutes past the San Juan de los Lagos exit and toll booths). It's a surprise exit. If you miss that take the Lagos de Moreno exit and then head back to Guadalajara.
If you can get to Ojuelos and Mex 70 you will have no trouble the rest of the way.
I just checked the maps on google against my rather old PEMEX maps and that Mex 57 bypass around San Luis Potosí doesn't seem to have a connection to Aguascalientes. Maybe somebody who has driven this route will respond with better information.
(This post was edited by jerezano on Feb 14, 2007, 1:42 PM)