fuel economy with passenger and trunk

[JimbosToys]

I thought I would share a little anecdotal info.
I finally completed the mounting of my $45 52L trunk on my tail. Not too hard, just took some time to find a round tuit. Needed it for GF's stuff.
Took a short intro ride with my setup this past weekend. 50+ miles w/o her (but weekend baggage/beer) on Friday, beach party Saturday, 50+ miles with her (140# fully dressed) on Sunday. 120 mile fillup - 1.6 gals for 75mpg. Best I have EVER had (fyi - I always have the Honda saddlebags installed). I do not think I was riding slower than usual, though I do know that makes a huge difference (drag rises with the square of speed).
My point is - seems my trunk definitively improves my aerodynamics. Have others experienced this in the real world? Anything else you have done that seemed to have a positive impact on economy?
Fyi, the trunk (and weight) does NOT seem to make the bike more squirrely on the highway and/or in crosswinds. Surprised (and happy) by that.
Jimbo
here's a pic:

 

[Red NC]

That Rear Case looks great. Is it compatible with the Honda Carrier?
More details and pics would be muchly appreciated!
Thanks

 

[chewybrian]

On a bicycle, an "aero-trunk" like the one below improves efficiency and top speed. Presumably, if you were burning gas, it would improve fuel economy.

So, it would not be a big surprise if your mileage was better with the trunk.

 

[JimbosToys]

That Rear Case looks great. Is it compatible with the Honda Carrier?
More details and pics would be muchly appreciated!
Thanks

I do not have the Honda carrier. The trunk comes with it's own wide plastic base that I mounted with a pair of brackets and arms. With the Honda carrier it would be easier, but you'll probably have to use two simple bars to get the holes to line up.

This is the one I bought from this seller - excellent service:
New Universal x Large Motorcycle Touring Scooter Tail Box Luggage Trunk Top Case | eBay

I think it matches the Honda saddlebags well and is not overpowering (I originally got the smaller one and it looked like a scooter bag). It's a little flimsy, but good enough for my use. Holds a lot, but I would be careful to not overload it with bricks or too much beer (would make a clever cooler for trail's end libations).

I might add some led's inside the red reflector to REALLY let tailgaters know I'm stopping.

I'll also add that my backseater now has a backrest and with 'slide off the back' security she doesn't crowd me anymore.

Will get to the bike and take a pic or two for you.

ride on. Jimbo

 

[JimbosToys]

On a bicycle, an "aero-trunk" like the one below improves efficiency and top speed. Presumably, if you were burning gas, it would improve fuel economy.

So, it would not be a big surprise if your mileage was better with the trunk.

Yep, a trailing fairing is common in all fluid drag reductions (airplanes, displacement boat hulls, racing bikes/cars, long-haul semi trailers, etc.). But I would not have expected this significant an improvement.

 

[ld_rider]

But I would not have expected this significant an improvement.

Since the improvement wasn't actually scientifically arrived at.....more than likely it is a bit bogus ;-)
I can change <nothing> on my motorcycle and get a significant change in my mileage even though I think I'm riding under similar conditions. The reality is that unless a bunch of variables are accounted for it is really hard to pin down a particular cause/effect, especially mileage.

My guess? Riding slower with a passenger is the real cause.

 

[fiah]

I wouldn't draw too many conclusions from 1 fill-up

 

[Nofear2trek]

I ride mine no matter what the mpg is. A couple more mpg here and a couple less mpg there, doesn't break the bank. I am just enjoying the ride!

Ray

 

[JimbosToys]

Since the improvement wasn't actually scientifically arrived at.....more than likely it is a bit bogus ;-)
I can change <nothing> on my motorcycle and get a significant change in my mileage even though I think I'm riding under similar conditions. The reality is that unless a bunch of variables are accounted for it is really hard to pin down a particular cause/effect, especially mileage.

My guess? Riding slower with a passenger is the real cause.

Fair enough - was my first reaction, as well. But I'm not sure. Same temps, winds, level ground, ethanol fuel, tire pressures, phase of the moon. I'll do it again and let you all know - promise.
What I wanted was to see if anybody had seen similar result.
And yes, I'm gonna ride it anyway!

 

[670cc]

Fair enough - was my first reaction, as well. But I'm not sure. Same temps, winds, level ground, ethanol fuel, tire pressures, phase of the moon. I'll do it again and let you all know - promise.
What I wanted was to see if anybody had seen similar result.
And yes, I'm gonna ride it anyway!

I think you are on to something, though. A trunk would close the air behind the bike better than an upright rider's back. My best ever mileage for a 292 mile tank was with a small tail trunk and no side bags.

 

[JimbosToys]

I think you are on to something, though. A trunk would close the air behind the bike better than an upright rider's back. My best ever mileage for a 292 mile tank was with a small tail trunk and no side bags.

Thanks for the input, Greg! Did you ever do a repeat to see if it was a fluke?
Given the fuel economy emphasis NCXers display, I am surprised this hasn't come up before. I'm gonna dig in.
Also, here are the requested mounting pics for Red NC:

 

[JimbosToys]

PS - the mounting parts wereca trial with parts on hand in my shop - need to be tweaked a little, mainly for looks!
PPS - the aluminum tape is on the tailpiece from when I protected the paint when strapping down a duffle bag.

 

[Red NC]

Thanks for the info an pics !
Really nice job there Jimbo

 

[JimbosToys]

OK. Update with another datapoint.
180 miles, just me (so no fill between me and the trunk), medium baggage load (tools, parts).
Averaged over 62mph on mixed back and 4lane roads (likely faster than the last report) because I followed some cars in a hurry (Hurricane Hermine coming!).
Got 69.3 mpg.
Not 75, but still better than my usual.
I think this is a real thing.

 

[JimbosToys]

Another run - 60 mph average - 70mpg