A change from 250 to 210 miles before the F-Trip is almost a 20% drop in fuel economy – which is quite a lot! I very much doubt that a change to a DNA stage 1 filter will have caused this all on its own?

Has the filter been over-oiled? Brakes binding due to the salty roads? Chain deteriorated? Are you being more throttle-happy? As you said, you can “feel the bike breathing better.” I’d guess the ambient temperature is also a lot lower on your commute recently, more so than when you had the OE filter in? Is it a short commute? That’ll make the negative effects of cold weather on fuel economy more pronounced.

I’m with RBJ on the cold weather conspiracy.

All engines have an optimum operating temperature, and the colder it is, the longer it takes to get there. Although the sensors and ECU take account of a lot of variables, the essential fact is that the fuel injection system is only fully efficient when the engine is at full operating temperature. When the ambient temperature is low, the motor requires a longer period of time to reach full operating temperature (and efficiency) —and it’s in that warm-up period that a lot of fuel efficiency is lost.

Colder weather increases friction too. The oil is thicker and more resistant to flowing when cold, so it’s harder to pump, which means more work for the engine. Rolling resistance also increases with a drop in ambient temperature, which isn’t what we naturally assume – usually we think of dry hot days as good for high friction (grip). Tyres, for example lose approximately 2psi for every drop of 10C, which increases rolling resistance and hurts economy.

Also, add to the above the fact the battery takes longer to recover from starting, so causes more drag from the alternator as it tries to get the battery voltage back to where it should be.

Having said all of that, I tend to get more mpg in the winter! However, I definitely know I ride less enthusiastically in the colder months, which kind of cancels things out.

__________________