On ADV rider forum, this kind of thread comes up pretty frequently.
For those who don’t want to spend hours and hours for reading multiple (and sometimes lengthy ) thread ,
here’s the very basic fact of hot weather riding.
The magic # is 93°F.
Below 93°F, it is relatively easy. (Wear mesh, or open all the vent, to get more air flow, and keep moving)
The wind is your friend.
Above 93°F, the wind becomes your enemy.
It is a simple matter of thermodynamics. Ambient temp below body temp (with delta of 5°F) gives heat-loss into ambient air.
And, if the air is moving around your body, there’s also evaporative effect.
Anything close to, or above body temp nets heat gain, and the more air is moving across the body, the more heat gained.
Think blowdryer. When it gets triple digits and you are moving at above 50MPH, think blast furnace.
That’s why some say full mesh gear works best and some say opposite.
However, if you are doing very short (less than 15 minutes, for example) ride, you may be more comfortable with mesh gear (with moisture wicking underwear, such as light weight merino wool or coolmax.)
Another important things,...
Please be careful and know the sign of heat stroke. It can kill you.
Hydrate yourself regularly.
There’s no magic. When it’s hot, it’s hot. Don’t fool yourself believing that lightweight mesh gear will protect you just like your regular riding gear.
Anyone who is serious about this topic, I recommend reading this article.
http://www.ironbutt.com/ibmagazine/IronButt_1002_62-66_Hot.pdf(same as the one posted by OP)
Also this one.
http://www.ldcomfort.com/pdf/LDComfortOnePage2013.pdf