With over a year of Versys ownership and monitoring my mileage I've noticed the gas mileage goes down in colder temperatures and been looking for a reasonable explanation. Has anyone else noticed this?

Most of the season I average about 4.7L/100km for mixed riding however mileage decreases to about 5.4L/100km in below ~10C/50F riding. I use heated gear and was wondering if the extra electrical load would impact this? Any other ideas?

assuming it's not caused by winterized fuel....

Not sure about motorcycles, but in cars, cold air is denser, therefore the MAF sensors read more air/oxygen and the ECU boosts the fuel to meet its target fuel ratio maps.

Colder temperatures can lead to lower efficiency due to lower operating temps with the bike. Thereve been multiple discussions over this as well, so I'd recommend searching the forums as well.

I installed a Thermo-Bob, not for fuel savings but for proper operating temperature.

After the installation there was no measurable impact on gas mileage, either good or bad.

Don't know about the scientific aspects, but I do know that when the mileage decreases, my temperature increases.

There are several factors. ECU's fuel mapping may overcompensate by adding more fuel than needed to maintain desired air/fuel ratio in colder denser air in relation to intake air temperature sensor input. Higher oxygen content to air volume ratio yields more available power, but does not decrease engine's fuel efficiency.
Longer warmups and colder running engine. Oil temperature is lower and adds operating drag in engine and tranny from its higher viscosity. Wheel bearing grease is thicker when colder. Drive chain is a bit stiffer, etc... Wind drag is increased in colder denser air. Also, tire pressure decreases by about 1 psi per 10 degrees Farenheit drop. Be sure to adjust cold tire pressure in colder ambient air.

I would say that TOO... except I believe it's TWO words... and a hyphen!

answer is simple hotter temps less fuel required, cold temps more fuel required, in EFI bikes its done automatically, i have a racing 2 stroke and i re jet the bike as above richer large jets installed in carby in winter leaner in summer, no other changes are made this is because of air density changes more dense air when its cold so more fuel required to maintain correct fuel/air ratio for smooth runing

ECU's fuel mapping may overcompensate by adding more fuel than needed to maintain desired air/fuel ratio in colder denser air in relation to intake air temperature sensor input. Higher oxygen content to air volume ratio yields more available power, but does not decrease engine's fuel efficiency.