I dont know if it is just me but both of my bikes were getting around 45 miles to gallon on highway. They both get around 40 now seems like that started around 2 months ago. I use exxon premium. What is going on? 2012 street glide and 2013 street glide

 

i never got any mileage with exxon, i prefer shell 93 myself. plus i put 1oz of marvel mystery oil to 5 gals of fuel, it lubes the top end and keeps the injectors clean.

living in Zoo Jorsey they put more crap in the winter fuel hens lower mileage.

but then again i really dont care about fuel mileage I Just Love To Ride !!!!!!!!

 

It seems to me that my bikes uses a bit more gas in cooler weather.

Another issue is methanol, when added to gasoline reduces MPG.

I think I read somewhere that a 10% mixture of ethanol to gasoline recduces MPG by 7% (in cars but that could also apply to bikes).

You may want to use the same brand of gasoline consistently when comparing MPG's.
Some guys I know swear that their bikes run better and get more MPG's when they use BP gasoline but I'm not convinced that is correct.

 

If the bike is set up properly it should give you 50 mpg on highway...

 

I usually see a similar drop in mpg during winter. I just attribute it to winter fuel blends here in CA. Happens every year and is always a 4-6 mpg drop.

 

I've found out it depends a lot what speed you usually travel. Some people ride at 70 on a flat land with very few overtakings keeping rev and throttle constant. Others travel north of 80mph and some short but more or less frequent burst to 85/90 with up and downhill sections. Add to this the effect of a short or tall windshield and mileage can vary wildly. On my dyna I can get 55mpg going at 70 but if I put the touring w/shield on and keep it in the 80/85 mph range I get around 45 out of a gallon...

 

If the gas you typically get suddenly has more ethanol in it, then you'll see your mileage drop. I seen it when Indiana went to a mandatory %10 and now I read that %15 is coming.

 

Texas gas is reformulated in the winter. I don't know if that affects gas mileage. I really don't care. My issue is how well does the bike run with the fuel I buy. I check my mileage on every fill up but only to track tuning. Both of my bikes get mileage in the mid thirties running 93 octane. They are tuned fat. Mileage can change radically on how I twist the wick. I noticed a change in one of my bikes from cam change and tuning. Mileage got really low. Almost thirty miles to the gallon. After a few tanks I got use to the cam change and was just cruising. Mileage jumped to the mid thirties because I was easing through the gears instead of hammering.

 

If you do not do a lot of wide open throttle it will get slightly better on mid grade. May even run fine on regular. The btu is the same for all grades. So if you do not need the upper grades you will get slight better fuel mileage. Driving conditions and your habits can make it change as much as 10mpg so it truly is hard to judge +/- 4 or 5. Least that is how it works for me. Interesting how much difference the stock compression rate can vary over some of these motors from one year to the next.

 

Same commute with 12 different ways to get to work through the NC countryside. Buy 93 gas anywhere convenient.

46 mpg summer, around 44 winter. I always attributed that to longer warm up times.