I had a co-worker ask me how long it takes to commute to work, so I downloaded the recent 5 years of bike trips and had a look. I deleted all the distances greater or shorter than my commute distance to eliminate errands and joy rides and then plotted by month in order to have a look at seasonal variation. Then to put some numbers to it I defined summer as June, July, and August and winter as December, January, and February and ran some averages. Looks like about a 15% drag for me, all things combined (temps, wind, stupid studded tires, pedal swap to platforms for the winter, etc.). I'm in central Indiana, max summertime temps are up over 100F a few days per year, probably 105F excluding heat index effect, lowest wintertime temps are probably negative digits a few days per year, lowest I remember is about -7F, ignoring wind chill effect, and that was just a couple months ago. Anyhow, it makes a fun picture and it explains well why I've always moved my wake-up time to ten minutes earlier on Thanksgiving weekend.