I used to run a Me55 Metronic 140/80 on the rear and I am pretty sure that is about the biggest tire you can run on a stock bike.  It actually rubbed on the brake bar for the first few dozen miles.  I can either get you the measurement or throw the tire on a chopsaw cut a chunk out and fax you picture of the cross section.  Or is the measurement 140mm??  Tire sizes still confuse me.  The tire caught a nail a couple of weeks ago but I havn't tossed it yet.  Plus, my M1 Sportec is  way stickier.

Yup....thats what I mean about using a hugger from a different bike. Hence the name...hugger...it looks like its hugging the tire, if you use a hugger from a different bike, the size contour will be different, SV come with a 160...much bigger tire than a GS.