For my 2007 s2k that has 17" wheels what size tires would I need for a 19" so that the wheel would still stay the same radius? And won't mess up my speedo

 

Depends on wheel widths. Also why 19's? 19's weigh significantly more decreasing performance in all aspects, ride harsher due to smaller sidewalls, and cost more than smaller sizes. 17's are IMO perfect for the S, but if you want bigger go no more than 18's.

 

^Agreed. 19's are to much for this car. I would assume it would be like a 215/35/19 front and 245/30/19 rear but thats just me guessing the step up from the common 18 sizes. I strongly suggest staying with 17's or 18's.