Tire size for race

this year I´ll race on portuguese championship of classic motorcycles with a Vespa (Sprint with Px engine , 175 pinasco…) and want to know what tire do you advice me to use on rear ! I´ll use Rally primary transmission (23 cogs) and px125 gears . my friends use 350.10 S1 but I feel they are to thin … what do you think about 110.80.10 ?