According to my owners manual, all 2003 FXD series have a 4.9 tank with a .9 gallon reserve. The exception being the wide glide with a 5.2 tank and a 1.1 reserve. I get about 40 mpg of mixed riding. Sometimes more sometimes less, and it doesnt seem to matter if I use ethanol free gas.

Like Apollo said, go to the reserve then fill up as soon as you can. You can calculate tank range easily and pretty accurately.

I fill up around 150 miles on my FXD just to be safe. Run really low just once and you will not be able to keep your eye off of the gauge.

The manual shows a low fuel light, but that is probably for EFI bikes.

 

Well, I finally was able to run it down till it started sputtering and I was at 129 miles, so I switched to my reserve and went and filled her up.

So with that being said, yeah I'd probably get 150 on a tank counting reserve.

Oh, and the stupid needle on my fuel gauge was about 1/8 tank past the E...