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How does humidity effect cooling on our bikes?

940 views 5 replies 5 participants last post by  Code Man 
#1 ·
Hi, Just coming out of a hot spell here in central California USA. Was 110f the other day. Only 98f today.

It's a dry heat so not that horrible to my body. Last summer visiting Austin Texas the humidity was very high & 98f just about killed us. Of course our body cools by sweating & evaporation, but what about our bikes?

Do they cool better in dry or humid air? That is at the same temperature.

Bike runs well in this heat, but fuel boils out of carb in 5 min. after shut down. Just tickle & it starts right up. The heat coming off engine at stop lights is horrendous, Even the gas tank gets hot after several lights, but doesn't really cause a problem. However idle must be set 1100+ or motor may tend to die at idle.

The hottest I've ridden in is 117f. a 200 mile ride. Bike did fine. I found I was cooler with my jacket on as the sun & air was so hot to the skin.

Been wondering about the humidity & cooling since the Texas trip. Lots of bikes on the road there.
Don
 
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#2 ·
Interesting question.

Water has a much much higher specific heat than air, but humidity in air is gaseous so that makes no difference. Humid air is less dense than dry air but if it's humid at ground level then air pressure is still the same regardless.

Humid air will have the effect of slightly raising compression though, since it will contract a lot as it's cooled by the evaporating fuel mist, perhaps even forming tiny water droplets which will expand enormously when they are blasted in the combustion chamber. On the other hand, the heat from the combustion is thereby very efficiently converted into mechanical energy and is carried out by the water vapour more efficiently instead of sinking into the combustion chamber and port surrounds.

I'd say any effect would be largely unmeasurable.
 
#3 ·
The hottest I've ridden in is 117f. a 200 mile ride. Bike did fine. I found I was cooler with my jacket on as the sun & air was so hot to the skin.

Don
Just wondering the same thing. Here in Hawaii it's around 85-90F in the summer, but also 60-80% RH. Noticed my water-cooled bikes run hotter than they did in LA (judging from the radiator fans turning on more). My car also runs hotter judging from it's water temp gauge. My air-cooled bikes all sound "rattly" to me, I've been wondering if I should bump the oil weight up a notch. As a physicist, I really don't see how the water vapor in the air makes any difference. Maybe it's all in my mind.

Also, won't help your bikes, but I started wearing a Joe Rocket summer jacket when I lived in LA. It's armored in the shoulders, elbows, forearms, and spine. The rest of it is an open mesh. The air blowing through it will really cool you down. Combine it with a wet t-shirt and it's downright chilly even on a desert day. They actually make a special vest, but truthfully a t-shirt works just as well. I think it's an earlier version of this one:

http://www.joerocket.com/mesh-jackets/phoenix-50
 
#5 ·
But as I understand it in terms of AC, the issue is that the system is expending energy in order to condense the water. Well, that's not actually very accurate, but you get my drift. As a result the actual temperature drop at the coils is smaller than if the air were dry. Just got into this while recharging my car's AC. It's old enough that it uses the now banned R-12, had to delve into the grey market of gas distributors.
 
#6 ·
Also, won't help your bikes, but I started wearing a Joe Rocket summer jacket when I lived in LA. It's armored in the shoulders, elbows, forearms, and spine. The rest of it is an open mesh. The air blowing through it will really cool you down. Combine it with a wet t-shirt and it's downright chilly even on a desert day. They actually make a special vest, but truthfully a t-shirt works just as well. I think it's an earlier version of this one:

http://www.joerocket.com/mesh-jackets/phoenix-50

I really like that jacket and it's at a good price. Thanks!
 
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