Increase in MPG/K&N

[fazersharp]

The first one though, I put winter tyres on the cage, which have blocks so soft you can move them with a single finger pressure, and get no difference in mileage between winter and summer

Could this be that your winter driving is different,slower, softer acceleration, due to ice ect. And so that compensates for the extra fuel the winter tyres take, also do you have air con in the summer and then not in the winter.