Yeah, it's been debated a bit, and it goes on still. However there's a simple experiment that you can do to see for yourself if it's hotter with the vents open (out) or closed (in).
1) Pick a hot day (e.g. 95+F).
2) Put the vents into the out position.
3) Go ride for a while to get the engine good and hot.
4) Get out onto the highway and ride for a few minutes. Notice how your legs feel with little to no wind hitting them.
5) Spread your legs out into the wind. Does it feel like your legs are heating up or cooling down?
Here's what I feel. I feel 100+F of temps on my legs. That's hotter than my skin temp, so my body has to work to dissipate it. So that wind feels "hot" not "cool". A hair blow-dryer that's moving heated air never feels "cool" to me.
See the following posts for Yamaha's stance:
Yamaha shows that even they have some confusion
Yamaha's simplified explanation If you want warmed air on you leave them in (closed). If you wanted warmed air not on you have them out (open).
The nice thing is that it's easily adjustable by the rider. So if you feel that having the vents in (closed) is cooler you can set it that way. There really are some riders who honestly feel that it's cooler with very hot air blowing on their legs, so they leave them closed (in). Doesn't bother me what other riders do, but when the air temps are 100+ around here I don't want that already hot air, which is then heated even more by the engine, blowing on my 98.6F skin. To me that feels... hot.
BTW, in my opinion the engine doesn't heat very cold air enough to make it worthwhile as a way to keep the legs warm in the Winter. So *for me* it's more comfortable to keep the vents out (open) all the time. To have them in (closed) makes the air too hot in Summer, and not warm enough in Winter. As always, YMMV. I just wish there was some way to cover the fugly screw holes that are exposed when in the out position.
Bunsen
