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Old 11-27-2012, 11:12 PM   #1
samwise2u
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Default Ambient air temp vs MPG

As the weather has become cooler a question keeps bouncing around in my head.

Ambient temp vs MPG. So this evening I typed the keywords into Yahoo search and read several articles that surprised me.

The "perfect" temp for MPG is 75 - 85. Anything above that and MPG decreases a bit. Anything below that and MPG decreases a bit until you get below 45, where the bottom falls out.

A surprising read.

I would have thought MPG would get better with lower temps. Anyone have two cents to contribute?
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Old 11-28-2012, 03:09 AM   #2
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A thread I was reading on here last week about cold weather starts may explain the bad mpg in cold weather. One reply stated that because the fuel is colder, it is harder to get it to atomize, to become a vapor rather than droplets. Thats why you need to choke or richen the mixture.


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Old 11-29-2012, 11:02 AM   #3
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Quote:
Originally Posted by rick View Post
A thread I was reading on here last week about cold weather starts may explain the bad mpg in cold weather. One reply stated that because the fuel is colder, it is harder to get it to atomize, to become a vapor rather than droplets. Thats why you need to choke or richen the mixture.


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With fuel injection systems you can't do either. The fuel processor takes care of all that stuff for you.

The colder it gets, the denser the air becomes, resulting in a more oxygen-rich content. I would guess that this actually requires less fuel, as it's the oxygen that supports combustion. I think what actually causes poorer gas mileage in low temperatures is a combination of things. The cold air is more dense, so the engine simply has to work harder to push the bike through the air. When it's cold, all the metal parts of the bike are cold, such as wheel bearings, etc., adding to the engine's workload, at least until things warm up. So basically, when it's cold, that engine just has a harder time making things go.

As far as poorer gas mileage in high ambient air temperatures goes, I've never heard of that happening, but it could make sense, as at high temperatures, the ambient air is less dense, therefor contains less oxygen, which would, in turn, require more fuel to sustain proper combustion. But that's just a guess on my part.
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Old 11-29-2012, 11:57 AM   #4
samwise2u
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Denser air is what I read too. It surprised me when I read it.

It was 39 degrees when I rode into work this morning. The air did not feel all that dense to me!
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Old 11-29-2012, 12:06 PM   #5
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I have always heard that for the most part engines run better and more efficient with colder air. I noticed in the past in my Camaro I ran better times at the drag stip when the temps were down then when they were up. (do not know if it coincidence or not) The times were only marginality better.
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Old 11-29-2012, 12:24 PM   #6
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The cooler air is better for combustion and performance. Colder air/hotter air really doesn't impact mpg once the bike is warm.

In colder weather you will have decreased mpg due to the ECM "choking" the engine and providing a richer mixture until the bike is warmed up. Once idle has returned to normal then you should, within reason, getting about the same mpg.

However, if making a bunch of stops you will be restarting a "cold" engine many times.

All that said, my experience has been that long trips in cool weather provide similar mpg. Short hops in cool weather provide lower mpg. Any trips in extreme cold will significantly reduce mileage because the bike really doesn't warm up. Then again, I don't ride in those temps, I typically stop riding around the freeze point.

Hot weather. Extreme hot you may see some reduction in mpg but that's mostly due to perfance reductions at those hot temperatures and just more twisty of the throttle.
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