28c is fine, and I doubt that you'll be the only one who feel that you'll be very slow, the point of a training rides is to encourage every single one of you to push it.
Go for it, everyone was slow the first time they start riding their bike seriously.
except maybe Nhatt, she's always slow.
Since when were you a lady or started going on forum rides?
Since when were you a lady or started going on forum rides?
;)