Poor fuel mileage

Whooshka said:

Last spring on a week long ride, a lot of it high RPM spirited riding, I averaged 42 MPG. There was also about 500, 80 MPH highway miles mixed in with the 1500 total miles. In the fall on a similar, yet mellower ride with the wife on the back I averaged 35 MPG. On a few short rides this spring I am still seeing 35. I started the bike the other day in the garage and saw 1 bar after a minute and a half, 2 bars at just over 2 minutes and 3 bars at just over 3 minutes of idleing. The temp in the garage was 62 degrees.

Is it possible my T-stat could be on the way out?

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Mileage numbers for your speeds seems typical, (mine is generally 48 mpg but speeds are more "conservative"), but for whatever reason(s) my two up riding mileage actually seem to increase slightly into the near 50 range.
I log and calculate every tank over the last few years since I've owned the ST.
Thermostat activity seems normal. Check into some of the other suggestions of tires, brakes, and/or throttle body sync.
One or two tanks (especially per the display) means nothing. A three full tank minimum is my standard for averaging mileage numbers. Filling routine is also very important as the amounts are relatively small fill variances can make big errors in actual results. My display always shows about 3 mpg less than my miles/gallons used calculations work out to. One of the very few vehicles I've ever owned that errors on the pessimistic side.

jettawreck said:

... for whatever reason(s) my two up riding mileage actually seem to increase slightly into the near 50 range.

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If your passenger is a slim and trim lightweight, I would guess that there may be an aero advantage that more than offsets the increased load on the M/C.

My two-up rides also yield better mileage. I attribute this to slower throttle application; no jackrabbit starts as I remember my dad telling me, and overall a less enthusiastic riding style.

Don B said:

If your passenger is a slim and trim lightweight, I would guess that there may be an aero advantage that more than offsets the increased load on the M/C.

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Well,...she used to be. "We" don't/won't discuss weight and/or size but she's about 5' 5" and aprox 30 pounds heavier than 30 years ago. Regardless, I think there is a real credit to the aero theory (especially since it was also my theory) as I notice a lot less backpressure when riding two up. There also is some chance of less aggressive accelerating, but I generally ride pretty conservatively even solo and the "instant" display seems to read a bit better at steady hiway speeds two up.

DavidR8 said:

My two-up rides also yield better mileage. I attribute this to slower throttle application; no jackrabbit starts as I remember my dad telling me, and overall a less enthusiastic riding style.

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Possibly. See observations/comments above. Never know for sure why, probably.