Bear in mind, fellow forum goers, that when the ambient temperature rises above body heat you are better to insulate your body with something than to leave it exposed to the sun, which is then slowly broiling any exposed skin.
Saw a couple on a cruiser one summer. It was pushing 40c. He was wearing the usual uniform (leather waistcoat, jeans, chaps, fingerless gloves and an ashtray on his head); she was wearing a leather thong, chaps and a leather bra, plus fingerless gloves and the ashtray. They must have been riding for a while because she was redder than a beetroot and headed for some serious sun burn.