Jerry Eichenberger
Serious Thumper
Offline
2006 S40. OEM windshield, saddle bags, Sportster
Posts: 2919
Columbus, Ohio
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Winter gas has less to do with poorer mileage in the winter than does air density.
Internal combustion engines run a fairly constant air/fuel ratio - remember, the only reason for gas in the first place is to get the air to burn.
The colder the air gets, the denser it is, meaning more air molecules in a given volume.
So, as the air gets denser, you have to put more fuel into it to get it to combust (maintaining the same air/fuel ratio).
A side benefit is more power - the colder the ambient air temp., the more fuel you have to burn = more power output from the engine.
That's also why mileage goes up in the summer, and with higher altitudes. Ride your bike or drive your car in the summer, up goes the mileage because the hot air, being less dense, needs less fuel to burn. But, power output declines because a lesser air/fuel mixture is going into the cylinder.
Best combo is a hot summer day at higher altitudes, like in the Rockies. If you can find a flat area with hot/high conditions (higher altitude also means thinner air), that's the most for your mileage, but the worst for power output.
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