My 2018 Low Rider does something similar. I don’t trust the miles left. It looks to me like the miles left is a windowed average and a very short window to err on the side of caution.

 

You are correct. I had Heritage on the brain. MY bad.

 

OP, here's the bottom line. Gas gauges are inherently inaccurate. What you need to know is "when do I need to get gas"? If you wait for the low fuel indicator to light you waited too long. It is best to go by how many miles you've ridden starting with a full tank.

I use one of my trip odometers as a "time to get gas" gauge. I have a 5 gallon tank and get about 38 mpg. So, theoretically, I can get 190 miles on a full tank of gas. I start looking for gas when I've ridden 150 miles. That gives me the time to look for the brand I want without the pucker factor that I'm on fumes.

So, for me, I use the gas gauge as a rough estimate of how much gas I have and the trip odometer to know when to get gas.

 

food for thought to just tell you about mine. On my 2018 street bob, I was also having an issue with my fuel gauge. It would not indicate full. The top bar would show up for a second when i filled up and then go away. Turned out to be a bad sending unit. My miles to empty would fluctuate like crazy because of it.

As for miles until empty, if i read the wiring diagrams and everything right, the sending unit sends a signal to the ecu, then the ecu uses injector pulse with riding habit to help determine how many miles you get on the tank.

 

That's about right. The ECU can count the time the injectors are delivering fuel, and it knows how many grams of fuel get delivered per second, per injector, so it knows exactly how much fuel has been used, and how far the bike has gone, plus what RPM it's done it at, air pressure, MAP etc...

So the fuel used/distance travelled calculations are extremely accurate.

What's less accurate is the fuel gauge sender knowing how much gas is in the tank in the first place. And that's pretty difficult to be accurate about as it's all sloshing around all the time!

 

My sport bike has no fuel gauge...

It has a gallons used counter that you have to reset every time you fuel up.

Has a 4.2 gallon tank(I think 4.2)... I start looking for gas after 3 gallons used, but I never leave on a ride without filling up because I ride farm roads and might not see a gas station for 100 miles. I dont tour on that bike...its like riding a park bench.

 

It's good to see that gas gauge accuracy hasn't changed for 2018

 

Who's is getting fantastic mpg on their 18 Softails? My 114 Heritage is consistently getting 50mpg even riding fast and heavy handed.

 

I'm still getting 48 even with the Stag II. Loving it.

 

I was getting 50 on the Fat Bob; looks like it's down to 46-47 after Stage II. Still fantastic. My last bike had less than half the displacement, 1/2 the horsepower, and 1/3 the torque, and got 47 mpg. For this bike with well over 2x the displacement, double the HP, and triple the torque, to get the same MPG -- it's fantastic.