With those rims you can put also larger tires than 90/90-10: I have 100/80-10 in my pk and they are fantastic. The problem regards the exhaust: in my vespa I could use those tires/rims only with a banana exhaust (the pk ets), since any other exhaust (polini right and lefthand, sito plus and others) touched the tire and not only for a few mm. Anyway the older smallframes such as special and your primavera had the exhaust more distant from the tire than the pk, so probably you shoud not have problems, but I cannot assure you. Very probably it should be all right with a banana, and possibly (a bit less probable) also with a standard exhaust or a polini-malossi-proma-giannelli lefthand. The rims 81018000 in my opinion make sense only with large tires, because they are rather offset so that if you use them with standard tires (in your case 3.00-10), or just a little larger (90/90-10) you may notice little equilibrium problems; with large tires (100/80-10 for small, 100/90-10 for largeframes) those problems are overcome by the advantages of the large tires (better stability in curves and less tire-blocking in braking).