I just got back from a 2600 mile trip and found a few things effect my milege...

1) The obvious, city vs highway
2) The amount of time the engine spends at full running temp. For example, I noticed the 2nd and 3rd tank while going down the highway always did better then the first. I attribute this to the bike running at "normal" operating temps while on that specific tank of gas. I found on the trip that it took about 30 min or so to get to this temp. (Note that the oil temp sending unit is in the pan)
3) Altitude - The higher up I got (colorado) the hotter my bike ran and the better my milage (Had a high of 57 MPG)
4) The bike does better overall if the RPM's are above 2500 for milage. That includes running it in 5th gear vs 6th for long distances.

The bike is totally stock.

Based on what your telling us, your mileage is about right what I would expect if most of your riding is 100 mile chunks or less.

 

My 1995 evo was getting 50+ with the stage II mods. Then I bored it 5 over, went with a little higher compression and ported the heads and now getting around 48. 80" runs side by side by side with the 96" bikes though.

 

In fact the fuel gauges are accurate but it's where the empty part is calibrated is what causes the problem. Some tanks may contain up to 2 gallons of reserve left when the fuel light is on. 1 gallon would be better, but all you have to do short of bending the float rod and recalibrating it is to get use to your own gauge readings. I seems to always repeat it's readings with the odometer. Miles per tank would only be meaningful if you ran it dry, but fuel cools the pump and it's not a bad idea to keep at least 1 gallon in there for that purpose. My milage varies between 41-44 with tmax, depending on my mood.
Ron

 

heres an accurate way to know your mileage. fill the tank, reset trip, drive 50 to 100 miles or so, then refill, divide mileage by gallons used to refill the tank, that will give you an accurate mpg. (well its the most accurate way i have found) i get 38 mpg

 

Also, when filling on the jiffy stand, the way I do, you always have to "manually" fill the tank way more after the pump click.

 

I haven't ever checked to see exactly how much I'm getting on a tank of gas. It usually takes around 4.5 gal to fill up though. Most times I lose track of when I bought the last tank. So, if I can't remember, I'm doing pretty good. Maybe I'm just senile, I can't remember

 

I have an '07 with the smaller tank, and although HD specs it at 5.0 gallons it holds more. My old '96 RK, which I believe had an identical tank, held 5.4 gal. when precisely measured. Anyway, my '07's warning light comes on when about one gallon remains, which may be why yours had not yet illuminated. Usually the gauge shows about 1/4 at that point, but it can be lower, so I wouldn't rely on the gauge when it shows <1/2. At the 1/2 point mine has used 3.2 gal., so it isn't linear.

Basically, you can depend on two things: First, if the light comes on, gas up ASAP regardless of what the gauge shows, as you don't have much left. Second, don't assume you have only a 6.0 gal. capacity. To find out, drain the tank completely and add gas one quart at a time like I did on my old bike. I wanted to know so I could ascertain exactly how many gallons I had in the tank when it hit reserve (carbed). The crux is to do your own tests so you know the behavior of your own bike, as I think two bikes will likely be different.

 

I just did an 1100 mile trip and averaged 50.5 mpg for the whole trip. This was mostly two lane mountain roads in Colorado and New Mexico. I logged mileage and fuel at each fuel stop.

Around town I get 45 to 50. My mileage increased by several mpg once I had over 2000 miles on the engine.

 

Strugis trip - best i got was 51.3. Traveled 2659 miles, averag mpg for the trip was 45 mpg.

 

on my '07 UC, the low fuel light typically came on around 1.25gal fuel remaining (5 gal tank). That said, it makes sense that your 08 with the 6 gal tank only took 4.8 gal.

I have kept the fuel receipts for every fill-up (yeah, I'm a techno-geek, so it makes sense...LOL) and it allowed me to get a real solid feel for what my UC would do for pure city, combined city/hwy and pure hwy riding.

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KoalaCowboy