Not quite that simple. It takes a specific amount of horsepower to maintain a given road speed, this doesn't change regardless of what engine is in it. The larger engine would be able to accomplish that same power at a slightly smaller throttle position, so the airflow and fuel requirements would be pretty close. The difference shows up in how efficient each motor is at that engine speed and load, the smaller engine is oftentimes better at converting that fuel into horsepower all else being equal.

 

As in my sig I have a 2011 SG w/103 and it has 2500 miles on it I'm getting 36 to 38 MPG but its still new to me and I am a little heavy on the throttle sometimes but it still beats my service van 10.5 MPG or my truck 17.5 so I'm mo happier then a pig in a mud puddle....

 

Around town riding 35-38mpg...like others, it depends on the twist of the hand.

I just rode to Orlando, FL from DC and got 38-39mpg at 75-77mph on the way down. Got 43+ on the way back at 75-77mph...I kept the vents open on the lowers on the way back.

 

My limited gets about 41-45 mph cruise set at 75 with about 45 lbs of gear and me at 245.
PCV power duals and Monster Rounds.
To me that's not guzzling, it's hauling ***.

 

I've gotten as low as 32 mpg running 75-80 mph into a strong headwind and as high as 52 mpg running 50-60 mph in north central Arkansas on my 07 stage I 103. I average 39 mpg most of the time.

 

On my '08 EGC I saw no difference in mileage when I went from the stock 96" to the 103' with SE255 cams. Of course, I can make it worse when I can't stay out of the throttle.

 

My experience is that I get pretty much the exact same mileage on my 2011 RGU as I got on my 2008 FLHX.

43-48 is the range. Depending on weather.

 

I am still breaking in the 2011 RGU but I have been getting low to mid 40's. Its been cool up here until today, so today's mileage was 46 on some main and back roads. Yesterday I had it on cruise at 70 and was getting 43. Hopefully once it breaks in I will stay in that range. I am still stock at this time.

 

I've been getting 41 mpg (which is ok with me)

 

Rode 200 miles yesterday!
Went to Tony Packo's for lunch....
Anyway i got 44 mpg almost exactly. Not bad when you consider the bike is barely broken in...
Abot the same mpg as my 2009, 96" FLSTC...