what is the primary difference between the Carrera 4 vs the Carrera 4S? Suspension?

 

firmer and more sportier, less cush, less handling

 

Well aside from the obvious 4 wd, and the (IMHO) numb-er and less attached steering experience that comes with the front drive machinery, the 'S' connotes firmer, quicker and a more intense chassis experience. The 'S' (in 2 wd or 4 wd) gets you more motor that is an exceedingly positive experience as well. For me, in a U.S. location that gets modest and seasonal rain only (and no snow), the 2 wd Carrera S was the way to go. I couldn't be happier.