Vetter Challengers seek to develop vehicles that get over 100mpg, can go over 70 mph into a 30 mph headwind and can carry 4 full paper grocery bags on board. My streamlined Ninja 250 can easily do this. (For more information on the Vetter Challenge check out motorcycle designer Craig Vetter's website at www.craigvetter.com )
But streamlined motorcycles aren't for everyone so in my pursuit to show how to make motorcycles more efficient and useful I decided to work on another, less radical project. I decided to limit my modifications to a few simple tweaks and see if I meets the goals of the Vetter Challenge with my 2005 Ninjette.

I started by raising the gearing from stock by installing a 15T countersprocket and a 41T rear sprocket ( vs 14/45). It has been my experience that the Ninjette can handle up to 15/37 pretty well. I then made a taller windscreen and fully faired in my front wheel. Now I was ready to make a detachable trunk that would further reduce my aerodynamic drag and give me lots of cargo capacity.

First I cut out a 1/2" plywood base with slot for the rear grab handle to pass through that the aerotrunk can be clamped down by pushin some slats of right size to force the base down tight. I decided on a 29" for the length. The width was 16", a bit less than my shoulder width. The front bulhead is just under my seated shouder height at ~ 18" at the sides and arching up to 21" at the center. The rear bulkhead narrow down to 12" wide, 14.5" at the sides and arching up to 15" in the center. I then cut a loading opening in the front bulkhead 10" wide x 15" high. If you decide to make your own aerotrunk make so that it is just shorter and narrower than your torso as you seat on the bike. If it sticks out past your body profile it will likely increase the air drag rather reduce it.

After attaching the front and rear bulkheads to the base with glue and screws, I skinned the aerotrunk sides with some very thin plywood veneer (~1/8", commonly called doorskin"). For the curved top I installed a wooden lath for a central spine. Then I hot-glued some treated sign paper to the spine and the top of the sides as a form for a layer of fiberglass. After glassing the top, I used some fiberglass strips to seal and reinforce the edges. Then I painted it and mounted on my bike using the inner wood slat clamps a long bungee cord hooked on the lower edges of the front loading opening, passing around around the foldout hooks at the seat sides.

The aerotrunk easily holds over 3 full paper grocery bags ( probably could stuff in 4 ). I made a cover for the front opening out of some coroplast. Initial testing shows I'need to refine the inner clamp so that bouncing doesn't make the them come loose. Fortunately the bungee cord backup is very secure.

I'll test out these mods soon and report how it does fuel economy wise. Previously I've done around 80mpg on my 100+ testing loop before the mods.

Looks like the front end will cause unnecessary drag.

Since you've got a big gap between your body and the trunk, you're going to get turbulence coming off your arms/shoulders. There will be pocket of energetic/turbulent air in the gap, and more turbulence coming off the sharp front edge of the trunk. Observe what happens around the front edge of a big rig trailer in the rain (one where they don't have the gap filler panels behind the truck cab). Same situation.

Were it me I'd sacrifice a little bit of cargo capacity in favor of a rounded front edge, in an attempt to minimize that turbulence. Ideally you'd have a teardrop shape, but that would really kill your carrying capacity.

If you're serious about aero and willing to deal with some inconvenience, think about a lycra body sock like the Easy Racers and Lightning recumbent bikes use.

Also investigate a material called Zote foam, aka Plastazote. Interesting stuff… you can mold it with a heat gun and it stays put. Soft enough to use as a gap filler, stiff enough to use as covers/fairings etc.

Lots of info on the recumbent bike club website I built some years back:

http://www.recumbents.com/mars

Look for the projects section.

Adouglas, You are spot on about the gap between my body and the front of the trunk. I was planning to use a backpack to fill the gap to avoid the turbulence. I may need to move the trunk forward some more or build up the front to fill the gap. Thank you for the materials suggestion and the link to the recumbent bike website.:thumbup:

I've been using the aerotrunk quite a bit lately and even took it for an overnight trip to the Gold country. I've built up the front cover so that it fills the gap between it and my back. I also added a brake light to the back of the trunk as the bike's brakelight was partially blocked. I should have some fuel economy numbers soon as I'm still waiting to go on reserve with over 320 miles on this tank. Its been very windy the past few days but the bike with trunk has managed it well. People go nuts when they see me load a shopping cart full of groceries into the aerotrunk.:thumbup:

Pretty cool :thumbup:

Does having so much of the weight that far back make your front end light?

That's part of the reason he gets great gas MPG. To reduce rolling resistance Vic wheelies every where.

^^^^ he's got it! Actually the trunk is pretty light , probably no more than 10lbs. or so. And the beauty of it is I can remove it very quickly if I want to carry a passenger or do some sport riding. I'm in Chicago until tomorrow, when I get back I'll weigh the aerotrunk and report in.

I refueled today after hitting the reserve position; I went 362.8 miles and need 3.99 gallons to top off the tank for 90.9 mpg. Not bad, I did one longer trip and the rest was just running errands. I did close up the gap between between the front of the aerotrunk and my back by adding some stryofoam padding. I also added a brake light as the aerotrunk partially blocks it.

I weighed the trunk today; it is about 10.5 lbs. I did the grocery shopping for the week today on it. I need to post some new pix as I have painted the aerotrunk ( silver of course ) and to show the new front cover. I also found a 37 tooth rear sprocket and I installed it on the bike today. Hopefully we'll be breaking 100 mpg shortly. :thumbup:

Here is a picture of the Silveraero ninjette with the aerotrunk.

Here is a picture of the Silveraero ninjette with the aerotrunk.

:thumbup: :thumbup: :thumbup:

Amazing efficiency after so few aero-modifications !!!

Half of my fuel money has been spent in molesting (bothering and annoying) the atmosphere and making a huge air-shake :( :( :(

Thanks Hernan! I hope to see some bigger improvements with it now

that I have taller gearing.

I've been riunning some errands with the bike when the weather has been permitting. Of note was some Christmas shopping that I did where I found the Keurig coffeemaker that my wife wanted for Xmas at a Kohls. I wasn't sure if the box was too big for the aerotrunk or not but it fit! Today I deliver 2 briefcases I sold on CL Ive been asked on some hypermiling forums to quantify the improvement that the aerotrunk makes. I will be doing some testing comparing identical runs with and without the aerotrunk to indicate the difference.
Merry Xmas and Happy Holidays

Today it was time to refuel: 330.2 miles/4.05 gal.= 81.53 mpg. This tank I didn't go on any longer rides, just running errands with it. I redid my front fender and and extended the front edges of the aerotrunk to close up the gap between my torso and the trunk. I need to do some more test runs to show the difference between having the aerotrunk on vs. off.

:clapping: Nice!

And it doubles as a nice backrest for when you get tired!

Since I'm not riding as much due to the weather I decided to start fueling more frequently to get a better assessment of the fuel economy of my motos. I recently adjusted and lubed the chain after running some errands. I refueled after going 173.7 miles using 1.80 gallons of fuel for 96.5 mpg. This was all with the aerotrunk mounted. I still need to do a run on the test loop that Alan and I use but this looks very promising.

I still need to do the A-B-A testing to define the exact benefit of riding with the aerotrunk but in the interim I'll be comparing the difference between with aerotrunk and not. Today I refilled after traveling 106.9 miles, using .957 gallons for a result of 111.7 mpg. This is the best tankfill so far with this moto's current configuration ( 15/37 gearing, enclosed front fender, aero windscreen and the aerotrunk ). I'm done with modifications for a while so I'll just ride with the aerotrunk off and see what the difference is.

Gonna be cool to see the with/without comparo!

Yeah, I'm estimating it should show around a 10% imporvement with the aerotrunk attached. On a hypermiling forum another rider got around 5% with a smaller and cruder tailbox.

I did a ride today with a buddy into the Delta ( aerotrunk removed) and topped off after getting back: 113.7 miles/1.549 gal.= 73.4 mpg . There were a lot of hills and the pace was somewhat spirited but it does seem to show a marked difference without the aerotrunk. I may run another short tank to see what it does during more normal conditions. I think my worst tankfill with the aerotrunk on was around 85 mpg so compared with this one ( 73 mpg) it shows a difference of about 16%.:thumbup: More testing to follow.

i've been traveling a lot for work and dealing with family matters but finally got the chance to do some riding on both the Silveraero/aerotrunk moto and the streamliner. My last 2 tankfills with the aerotrunk installed were 94 mpg and 86 mpg. I've removed the aerotrunk for the next tankfill to better evaluate the differenceimprovement that the aerotrunk makes in fuel efficiency. The past brief test indicated around a 15 % improvement.

Have you looked into adding a bodysock? I bet you could attach the front edge to your windscreen, and the back edge to the trunk. It would (I think) almost eliminate any issues with the gap between you and the trunk.

A lot of us recumbent riders use these on our bicycles. I can find you some links if google doesn't help.

@Worldtraveler, Thanks for the advice! I'll have to look into bodysocks, particularly when I compete with my streamliner. This project is mainly about showing what can be accomplished with some simple modifications but the bodysock sounds like another improvement I could easily add to the streamliner for more drag reduction.

I haven't updated this project in a while but I've been using this moto a lot more as I do more work on my streamliner. The utility of the aerotrunk allows me to carry 90+% of the stuff I need to do for work or running errnads. The aero benefit of the aerotrunk is proven so I usually just leave it installed most of the time.
I seem to be getting around 90 mpg. Yesterday I refuled after hitting reserve : 380.2 miles/3.97 gal.= 95.8 mpg.

Now that it's getting cold here I'm thinking about expanding my windscreen so that my hands are out the airflow. It got into 20's so my gloved hands about froze after a 40 mile ride.

Update time! I ride this moto a bit more often than my streamliner as it handles better and can carry about the same cargo load. It continues to deliver relatively high fuel economy with the flexibility of the removable aerotrunk.
Some recent highlights: I had my brother ride the Silveraero project at the Hollister Vetter Challenge and he finished third of all the gas-powered motos behind Alan (172mpg)and me (162 mpg ). He got 142 MPG but I suspect that this was an artificially high reading due to fueling errors. Still, outstanding!

Last week Alan wanted to see how a Honda CFR250 would do on our test loop . I rode the Silveraero and got 102 mpg with the aerotrunk removed. The CFR250 got 89.8 mpg and Alan on his streamliner got 142.8 mpg.