Originally Posted by PeterW
Cotton T shirt. Buy water as needed at gas stops, pour water on T shirt, ride.
I live in Oz, 35 isn't hot :), 45 is ... it works, worst case the shorts get a bit stinky, toss them. Doubt you'll find anything more effective.
I agree with this. Buy a heavy cotton 'sweatshirt' (zippered? maybe 2) big enough to get over your gear. Cut the cuffs off the sleeves as you like. Cut the collar open enough for comfort. Soak the thing in water until fully wet and dripping and put it on. The evaporative cooling effect at 20+mph windspeed will be stunning. As long as you are not in an actual desert, it won't dry up as fast as one might think. Downsides are that it doesn't work well unless wind is blowing on it. So, do not expect it to be great behind a big fairing. Any 'coolness' needs to be transfered thru the gear to the skin. Armor will tend to prevent that. And your gear has to fit close enough for the effect.
Another technique used by long distance riders in the USA southwestern deserts is to stop at a convenience store for a bag of ice. Use some of the ice to fill all/most the pockets of the gear. Lay the remainder of the ice in its bag in the rider's lap. Some riders lay a bit of insulated wrap over the ice bag to keep the cold in and to keep the ice from melting in direct sunlight. This works pretty well behind a big fairing. Depending on conditions and needs, they stop for more ice as they want and can find. These riders also have a keem appreciation of keeping themselves hydrated properly. See IBA.com for a variety of body heat regulation tactics.
Some riding suits have an exterior layer that will hold water for a while if soaked. My Roadcrafter rides about 10F degrees cooler than ambient when the outer layer is soaked.
Actually practicing and experimenting with the tactics before you really need them is most helpful in knowing what can be done.