welll, since you aren't going into specifics, it's hard to answer. I think almost anything goes any more. I think there are bra tops that would be fine really as a top, if you don't mind sunburn and road rash.
I've seen enough guys with transparent backsides on their shorts

for me personally, short sleeve jerseys and shorts are my limits; but I've seen plenty of young gals showing a lot more skin and it does not bother me (unless i start thinking of wrecks!!)

Some guys will be inappropriate even if you wear a burka