I wanted to share this post I copied from a Facebook Vrod group made by the owner of Unlimited Engineering, maker of the 5.3 gallon conversion kit for 02-06 Harley Davidson Vrods.
"Here's the deal with tank size and gauge operation.
The factory tank, if you run it out of fuel, you'll put 3.4 gallons back in it.
The fuel pump is a constant on type pump. Fuel cools this pump. If you run it low on fuel a lot, you'll burn up the pump. As many have found, HD isn't making this part anymore and even when they did, it was a $600 item. You really want to keep about a gallon of fuel in your tank at all times. I consider this gallon my 'reserve' and only use it in emergencies.
So, 3.4-1=2.4 gal of useable fuel. Most vrods get between 35 and 40mpg. So, you are really looking at under 100miles of range. Yes, some bikes do a little better on mpg and can squeak out a little more.
Increase the capacity to 5gal and you get 4 to 4.25 gal of useable fuel (the Unlimited Engineering tank grows a little w/ exposure to gasoline and will normalize at 5.25gal total capacity.)
This explains how w/ the UE 5gal kit most are getting about 160miles of range. This is enough to ensure you are one of the last bikes in the group to need fuel instead of being the one who needs it first.
The fuel gauge is another topic that needs to be understood.
The gauge is driven from a float and a long resister. As the float rides up the resistor resistance goes down. This is what tells the little gauge what to do.
So first off, there needs to be enough fuel in the tank for the float to actually float. That's about 3/4 to 1 gal in the UE tank.
Second thing is that this long resistor gets oxidized over time. As so many of you have complained, this plays havoc on the gauge. It will wear the oxidization off in spots, and not in others, makes the gauge go crazy. The solution to this is simple, clean the sensor strip about every two years. The UE kit has instructions on how to do this and some scotch bright to do it with, but the short and simple on it is take the scotch bright, scrub the strip a little to remove oxidization and wipe it down. Very simple to do when the fuel pump is already out of the tank.
So, if you want optimal performance from the system, get a UE 5gal tank, clean your sensor strip. Then you can ride until the gauge is reading just before E (way below the 1/4 light) and when you stop for fuel you'll put around 4 gallons back in. Your gauge will read properly and you won't have to push a 600lb v-rod because you ran out of fuel. Life will be good."