Why did my mileage decrease?

[Jim Bronson]

I checked my mileage today for the first time in quite a while. It had always been around 40, but today it was around 35. That is a big drop! I'll check it at the next fill-up probably on Sunday and confirm the readings, but I'm wondering what could cause such a drop. The bike runs fine as always, and I haven't had any engine work done. I haven't change my riding style much, although I do get on it once in a while and hit triple digits. I can't see any reason it should drop so much. Any ideas?

[rigidthumper]

AFAIK, Fuel blends in the winter contain additives that make the cold fuel vaporize easier, which hurts mileage. I've always had better MPG in the summer than winter.

[Ohio HD]

That and cooler ambient temperatures cause slightly richer mixture throughout warm up and at cruise to some extent.

[Jim Bronson]

Yes, we do have "summer blend" and "winter blend" here. I'll wait until I see the announcement of the change and hope it improves. As far as ambient temps, I seldom ride below 50 degrees (50 would be a cold morning). I'll keep an eye on it. Maybe both factors combined are the cause.

Thanks.

[Hossamania]

One tankful is nothing to get too concerned about. The key to checking mileage is long term record keeping. I always do a cursory check every fill, not exact to the tenth, but close enough. (I always use my trip meter, I don't rely on the guage.) I occasionally get a tank that is substantially less than normal, I don't really worry about it, just ride on and check it next fill, usually back to normal, sometimes even better!

[Coyote]

Could be you filled up at a pump that's  cheating and reading more gallons than it actually dispensed.

[Jim Bronson]

Thanks for the tips guys. I'll pay more attention for a while and see if I can get to the bottom of it.

[Hossamania]

Same gas station, same pump? Same riding conditions exactly? Any headwind? When is the last time you checked your air filter, or changed plugs? Doubtful it's playing a big part, but a small piece here, a small piece there, it adds up. Throw in a changing blend of fuel, and it seems a big jump.

[Jim Bronson]

Same gas station, same pump? Same riding conditions exactly? Any headwind? When is the last time you checked your air filter, or changed plugs? Doubtful it's playing a big part, but a small piece here, a small piece there, it adds up. Throw in a changing blend of fuel, and it seems a big jump.

None of the above factors change much this time of year. I did clean and oil the air filter recently, but I haven't looked at the plugs in a while. The biggest factor would probably be the gas blend. I usually use the same station but not necessarily the same pump. Stay tuned...

[Scotty]

Jim you haven't been snacking to much and put on some weight as that kills your mileage as well. 

[smoserx1]

An other thing in cold weather the air is more dense so on a mass basis more air goes through your engine.  If the A/F ratio remains constant, more fuel will be used and more power produced.  But even so I usually measure my gas mileage every fill up and occasionally I will have a  result that deviates more than expected.  Things like old plugs and dirty air filters tend to result in a slow derogation over time, not a one time surprise result.

[biglew55]

One tankful is nothing to get too concerned about. The key to checking mileage is long term record keeping. I always do a cursory check every fill, not exact to the tenth, but close enough. (I always use my trip meter, I don't rely on the guage.) I occasionally get a tank that is substantially less than normal, I don't really worry about it, just ride on and check it next fill, usually back to normal, sometimes even better!

Great advice, Hoss.  I track every tank via Fuelly.com.  over the last several years, a tank can vary from 29 to 45 MPG. 

Depending on the particular blend you filled up with, and how long you left it in the tank, and how you rode that day, and how the weather was and if you had to much turkey over the holidays, etc., There are so many factors that contribute to a single tank of gas that it's hard to say.

[Jim Bronson]

I usually fill up weekly. I checked it on Sunday, and it's back to 40. 

[PoorUB]

Could have been simply crappy gas. I was on a trip, bought a tank of gas on got really bad MPG that tank. Next fill was fine. Went from 40 MPG to something like 27 MPG and back to 40 again. I remember  the amount of fuel seemed reasonable for the miles when I filled.

[Hossamania]

I usually fill up weekly. I checked it on Sunday, and it's back to 40. 

So all good!

[Hossamania]

I just reread the original post. A drop from 40 to 35 mpg. Not a big drop for one tank of gas, nothing to get too worried about, as you found out, just an anomaly that occasionally happens.

[Jim Bronson]

I'm going with the crappy gas theory. It was a good education for me. BTW, premium cost me $3.87 today at Mobil. 

[Hossamania]

That got pricey in a hurry.

[HogMike]

One our members was complaining about going from high 40's to low 40's after we did a little work on the exhaust system.

Finally figured out that he rode all the way home Sunday on the freeway in 5th instead of 6th!
The bike was so quiet with the addition of stock mufflers he didn't know he had a "freeway" gear he could use at 70mph!

 

[kd]

I'm going with the crappy gas theory. It was a good education for me. BTW, premium cost me $3.87 today at Mobil. 

Stop whining my friend.  We're at $1.484 per liter ($5.43 CAD / $4.13 USD per us gallon) for premium where I live.  I'd say you have it pretty good.