Interesting results this weekend. Car was on empty with ~19 miles flashing on the dash after some distance driving and an event prior to this. Decided just to fill up fully because I'd be driving a hour, running an event with 9 runs, driving back, then doing the same the next day with 6 runs Didn't want to be partial filling ~5 gallons both mornings.
Ended up getting my top finish ever at a local event. This is out of at least 100 events at this particular location location. The first day was my 3rd best out of ~100 too. Tank was virtually full on day one and at just over half on day two during runs.
Definitely not scientific testing and no real "control". I can't say the extra weight was slowing me down that much. Given @
Locust's data point, I'd say maybe a tenth or two may have been out there given everything else equal with that full tank.
One very subjective thing I'd like to note was slaloms and transitions felt better with a full tank. Felt. I can't put any numbers or times behind it.
I can see how at a national event you'd want the lowest fuel level possible to limit sloshing AND reduce weight. Best of both worlds.