Here's my take on the science, my opinion, and an EASY way to test on your own.
My take on the science:
I think that motorcyclists and skydivers are very keenly aware of what Wind Chill Factor is all about. If I'm in 30F air that isn't moving it doesn't feel all that cold - I could easily survive with a light jacket and light gloves. But bust out a fan and blow that same 30F air at me at 30MPH and suddenly I'll be wanting to put on a thicker layer of insulation, preferably something wind-resistant. The colder moving air pulls heat from a warmer object faster than still air does.
Along the same lines, a convection oven will heat up food way faster than a regular oven since the warmer moving air transfers heat into a cooler object faster than the still air of a standard oven does.
When the air rushes past the FJR's radiator and engine it picks up heat, and then that heated air gets directed somewhere. If you have the side vents closed (in the inward position) then air that's been heated is hitting the legs moreso than if the vents were in the open (outward) position.
I think that we all can understand the above. The point of contention is whether having the air that's been heated blowing on the shins is preferable to deflecting it away (somewhat) from the shins.
My body is supposed to be running at a constant 98.6F. However, air temps that high feel hot to me since my metabolism requires that I be able to release heat from my body at all times. So I prefer the feeling of air that's in the mid to lower 70's while at rest, or the mid to upper 70's at higher wind speeds. We're all different so your comfort range may be different from mine. Air warmer than that feels warm since it's not wicking heat from my body as quickly as I'd like. And at 99F and up the air is actually warmer than I am, so the air tries to put warmth into me - yuck! At that point I'm surviving due to the cooling effects of perspiration.
I don't know how much the air that comes off the engine heats the air. For the purposes of this discussion that would be helpful to know (anyone have a thermometer that they can strap to their leg?). But if I had to guess I'd say that when the FJR is moving the air that goes out the vents has been raised in temp somewhere between 5F and 15F, depending on speed. So, if it's 40F outside and the air gets raised 5F to 15F, then the air coming out the vents is around 45F to 55F, and that's still a might chilly for my tastes. If it's 95F outside and it gets raised 5F to 15F then the air coming out of there is higher than my core temp, and so therefore it's trying hard to put heat into my body (like the convection oven).
My opinions about the vents:
1) If the temp is above about 80F degrees or so I definitely prefer them in the outboard position. I don't want the hot air hitting my shins.
2) If the temp is below about 60F degrees or so I definitely prefer them in the outboard position. I don't want the cold air hitting my shins.
3) If the temp is between about 60F and 80F I kinda don't care so I leave them in the outboard position since it's less work.
So, mine are in the outboard (open) position at all times. (In spite of those fugly exposed screw-holes.)
The EASY way to test on your own:
One problem with testing how something feels (or sounds, or tastes, or practically anything to do with our senses) is reproducibility. If there's too much time between 2 tests we tend to not be as able to accurately gauge the difference between 2 samples (some people are good at it (e.g. people with perfect pitch), but they're outside the bell curve). If someone replaced the light bulb in your garage with one that was 50 lumens brighter or dimmer while you were on vacation, would you notice? Almost certainly not, even if they told. But if you switched back and forth between the 2 lights in a very short period of time (e.g. less than a few seconds) then you almost certainly could tell the difference. The same is true for temps. If you let a few minutes go by, your perception of a previous temperature becomes less reliable to compare a new sample against. (I won't even go into the whole "power of suggestion" thing, which can throw some amazing monkey wrenches into experiments in which people are the sensors.)
It's been suggested to have one side vent be out and one side in. However, using 2 different limbs to measure a temperature isn't necessarily very reliable. That's easily testable: Filled a pan with 80F water and set it aside. Fill 2 other pans with water, one icy cold (full of chunks of ice) and the other fairly hot (105F to 110F). Put one hand into each of those extremes and let them sit there for a minute and then put both of them into the 80F water. Each hand will report to your brain a different story - the hand from the cold water will say that it's been put into very warm water, whereas the hand from the hot water will report that it's in rather cool water. Same water but measured by different hands with different experiences, yields different feelings.
What you CAN do is this (and I've suggested this same thing in several posts on the subject, though not with as much background detail): Put the vents in the outward (open) position. Get the engine up to operating temps by riding around for at least 10 minutes or so. Then get up to the speed at which you want to test. Then test by extending your legs out into the air stream for a minute or so. It's the same air, blowing past the same radiator and engine, but there's far less time for your legs to forget the previous test. If it's 100F outside and your legs tell you that having that 100F air that's been heated by the engine feels cooler to you then by all means stop and move the vents inward. My legs tell me that the air is trying to put heat into them, so I leave them in the outward position on hot days.
When it's 40F outside, it feels *to me* that the engine doesn't heat up the air enough for it to be comfortable, so I leave the vents out on those days as well. On those days between the extremes it kinda doesn't matter, so why go through the hassle of moving.
Of course, your milage (er... senses) may vary, and I can think of a few other minor issues with the experiment, but I still think that it's basically a good valid test. If you notice a difference then cool - act on it. If you don't then by all means leave the vents closed - I think it looks better that way (again, your senses may vary on that point as well
)! I put forth the above explanations and tests that you can do yourself so that you can at least make an informed decision and test for yourself.
Bunsen
