New tires bad mpg

[pat8228]

I just put new PR4's on my bike, plus a Givi topbox. Mile MPG went from an average of 41 or 42 mpg down to around 38 mpg.
Is this normal? I thought maybe I tightened the axles too tight. I loosened the rear axle 1/4 of a turn, but didn't change anything. Plan on loosening the front later today.
Could the new tires and the Givi box cause me to loose 3 to 4 mpg?
Thanks

[VirginiaJim]

Never heard that one on our bikes, but as my Prius tires wear down the mpg gets better and I can usually see a decreased mpg when new tires are installed, at least for a good 20k miles or so.  There are such things as low rolling resistance car tires but I've never had any experience with them.

What tire pressures do you use?

[B.D.F.]

A topbox is pretty draggy (non aerodynamic) so it may well cause a noticeable decrease in fuel economy. I am running a Givi 55 but honestly did not pay any attention to the mileage when adding it so do not know if it made a difference or not. But given the crud on the back of the box, it sure does act like the air flows around it pretty badly.

Depending on where you are, the temps are also starting to drop, especially at night. The C-14 seems especially sensitive to outside temperature regarding fuel economy so that may be at least a part of what you are experiencing too.

Brian

I just put new PR4's on my bike, plus a Givi topbox. Mile MPG went from an average of 41 or 42 mpg down to around 38 mpg.
Is this normal? I thought maybe I tightened the axles too tight. I loosened the rear axle 1/4 of a turn, but didn't change anything. Plan on loosening the front later today.
Could the new tires and the Givi box cause me to loose 3 to 4 mpg?
Thanks

[lather]

For what it's worth I also experienced my worst mpg after installing PR4s but never considered that it could be due to the tires until reading this thread. I have a Givi topcase but have always had it so that was not a factor. I attributed the poor mpg to prevailing headwinds on a 3000 mile road trip we took. However the PR4s do have unusual tread patterns and that could possibly increase rolling resistance. Due to the spacers used on the axles it is my impression that it is not possible to create wheel bearing drag by overtightening.

[Cold Streak]

Loosening your axle nuts below recommended torque is a really bad idea.  I hope you don't ride very far with them like that or you may become a statistic which is far worse than your mpg stat.  I think adding your top case was probably the biggest factor in the fuel usage.  Wind resistance or drag is the number one culprit for poor fuel economy.  Take the top case off and see how that affects it.

[JoeRau]

Did you go from a 50 series to a 55?  That could cause the decrease in calculated MPG. 

[Pilgrim]

Have they started changing to winter formula gas already? 
Thats good for a decrease in MPGs.

[MAN OF BLUES]

I just put new PR4's on my bike, plus a Givi topbox. Mile MPG went from an average of 41 or 42 mpg down to around 38 mpg.
Is this normal? I thought maybe I tightened the axles too tight. I loosened the rear axle 1/4 of a turn, but didn't change anything. Plan on loosening the front later today.
Could the new tires and the Givi box cause me to loose 3 to 4 mpg?
Thanks

Go back and tighten that axle to the rated torque, and don't  loosen the front one either.
The axle torques have no effect on rolling resistance, loosening them will cause bearing failure, and dangerous mechanical issues.

[Scaffolder]

I'd blame the trunk. If it is cold where you are you have put the windscreen up too.
32 degrees during this mornings commute.

[tomp]

Have a factory/Givi topbox, as well as a V-stream tall shield and added Laminar lip on mine, and unless riding way over  highway speed limits, I average 42-43 MPG, all the time.  Also have Z8's with 2400 miles on them.  I hate to think that PR4's would change mileage that much, as those were to be my replacement tires.   tp

[maxtog]

When I went from stock to PR4GT, my mileage didn't change at all.  I suspect you either used non-OEM tire size or it is the drag of the top box.  (Plus there are lots of other factors that will cause MPG to vary).

[Marco1018]

I have has the bt-021 (stock), bt-023 gt and the pr4 gt and have not noticed a chance in mpg.  I little drop when I went from the 50 to 55 but that is to be expected.

[concoursbdh]

Never have noticed a change in fuel mileage from tires but certainly have briefly after installing a new slip on!  :)  Just have to hear that new sound!

[pat8228]

Thanks for every ones advise. I do have oem size tires. the Givi box is the 55L.
Thanks again.

[C14lvr]

50 to 55 series rear won't cause a change like that.

Now, On mine, the biggest thing I've noticed that causes my mileage to drop is 2 things...
1) riding into a headwind with my tall CB windscreen all the way up.
2) running ethanol, 87 octane gas instead of pure 91 octane gas.

My mileage drops dramatically when experiencing either.

[pat8228]

I think it may have  been bad gas! After I filled back up with fresh gas it's back up to 41.4 on average.

[tomp]

Glad to hear that.  Sure didn't want it to be a tire problem...

[B.D.F.]

I've had bad gas.... or so I have been told.

Brian

I think it may have  been bad gas!

<snip>

[tomp]

I've had bad gas.... or so I have been told.

Brian

My mother always told me ,"That's OK. There's more room on the outside than in."

[maxtog]

My mother always told me ,"That's OK. There's more room on the outside than in."

Are you sure that wasn't Shrek?    https://www.youtube.com/watch?v=3lHH5p8gU5A