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Old 08-22-2016, 04:37 PM   #1 (permalink)
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CBR250R Utility/Aero Mod

Hey everyone!

Currently, my one and only vehicle is a '12 CBR250R, and as much fun as it is to blast around on two wheels, I had to do something to make it more usable (read: car-like (cringe)).

So in my attempt to do so, I searched for cargo carrying options available for this bike. Being the cheap-skate that I am (not a bad thing, I promise!) I shuddered at the retail price tags of what I found commercially available for this bike. Being a DIY guy whenever possible, I continued on.

I stumbled on CBR250R.net, specifically Sendler's build thread where he made a rack from a polyetheline cutting board. Intrigued, I continued on to find that the next person made a bigger tray, then finally the last post was a box affixed to the pillion seat.

Inspired, I took some seat measurements. With these in hand (15-16" wide, 15-24" long (without hanging off the end too far) and a guess of 10" tall), I went to the web, searching for something that might work for me.

I finally came across the Plano 56Q Sportsman Tote. Perfect fit. 15x24x13. Bit taller than expected, but whatever. It'll fit more stuff. Additionally, it seems like it'll fill the low pressure spot behind me pretty well.

I picked it up this morning with some mounting hardware (two J-Bolts, nuts, and washers) and a ratchet strap. The J-Bolts hold on to the rear handles as seen below, and the strap is threaded through the metal pillion seat lock thing like TestBacon did.

(Upload failed me here, so I had to link. Apologies in advance for any inconvenience)

http://i.imgur.com/zVxvuh8.jpg - Profile
http://i.imgur.com/qt26K7Z.jpg - Front
http://i.imgur.com/9cFEwyu.jpg - Close up
http://i.imgur.com/LjgwSCd.jpg - Under rear
http://i.imgur.com/CfHgMm3.jpg - Inside

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Old 08-22-2016, 04:47 PM   #2 (permalink)
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I nearly forgot:

Since the front of the tote sits on the seat where it crests in the middle (Like the carat ^ symbol) I used some cheap "concave door bumpers" to stabilize the front.
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Old 08-24-2016, 07:03 AM   #3 (permalink)
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Love it! Love it! Love it!

Very practical and useable and less obtrusive than most top boxes. Added to that, you'll find that it will be much, much more FE than a saddle box or bag or a traditional box that sits behind the pillion seat. In fact, looking at the picture and where you'll be seated on the bike in a forward position, it looks to me that you'll significantly lower the drag when riding on the highway.

I'm the one with the milk-crate-type that's strapped to the pillion portion of the seat on a CTX700. My bike makes my installation easy, because the entire seat comes off via a keyed latch. I just took the seat off and used lashing straps to wrap the crate around the seat exactly where I want it to sit. I use one piece of twine in the back around the license plate holder, but your underside picture gives me an idea for more stability and better look, because I too have pillion grab bars and so I can hook/bolt around my grab handles and delete the twine.

I need no more than a crate, because I can garage my bike at home and at work, but back before I tried to sell my CTX700, I had a similar box to yours strapped to my seat. What I ended up finding was a Dewalt Tough System 08204. It was very strong and water tight and ended up being about 55-liters. The biggest fault in the Dewalt box was that, being designed as a tool box first, it had some grooves and indentions in it that made it a bit smaller on the inside than on the outside. I took a knife and cut out the grooves and ended up with a suitable 55-liters. I don't have pictures of my bike with the box, because my computer has since crashed and I had deleted them from my camera.

When I went to the FE Challenge in mid-Ohio 2014, I had that Dewalt box on my seat and a short windshield. I tucked during the ride and achieved 96.9 mpg by my own recording data. Keep in mind, this is a 670 cc motorcycle. I am confident that without this box, combined with tucking, I could have achieved no more than 83 mpg on that bike, because that's as high as I'd ever achieved and that was on friendlier mpg rides than the Vetter Challenge ride.

I desparately want to build a tail like Sendler, because I feel my mpg can be optimized further with a tapering tail that will be even more useful than my crate, but I don't have his skills, and I've got to do some drag research, as one can make things worse if one is not careful. One must know the distance and angle to taper, lest turbulence could actually be made worse than stock. I also have to figure out how to build a tail that will allow me to easily remove it for weekly chain maintenance via a lift stand or build it so I don't have to remove it.
Again, love your box. Great job!

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Last edited by gregsfc; 08-24-2016 at 07:12 AM..
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Old 08-24-2016, 11:44 AM   #4 (permalink)
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Hey I recognize that bike! One of the many stops I made during research was that thread, actually. I'm glad you like my build. The only real gripe I have is that it's a bit of a pain to mount/dismount my bike with the box on. I'm considering moving it back some, but that would involve more holes in my box, compromising strength and water-tightness.

From my butt-dyno, the bike feels like it does cut through the air a bit better than before. I could totally be possible that I'm just not paying attention to my throttle hand!

Given the shape and position of my box, I think I might be able to attach a "tail cone" if you will, to the back of the box for a bit better aero too.
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Old 08-26-2016, 07:17 AM   #5 (permalink)
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Thanks for reminding me that my lost pictures may have been posted on a forum. Found them via Google search.

Tail cone would be best for me also, as I need easy removal to leave room to operate my lift stand and to hold the bike from the rear to do so.
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Old 08-26-2016, 07:59 AM   #6 (permalink)
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Good job Ninj4geek finding that box and executing the install.

I've been comparing your box to the one I had. The Dewalt 08204 Tuff System box. Your box is slightly wider, considerably longer, and considerably shorter (+.8 wider, +2.6 longer, and 1.9 shorter). Overall, my Dewalt calculates out to 4832 cu inches and yours 4680; exterior dimensions, if the Dewalt specs are accurate. But in reality, your box almost certainly has more interior space than the one I had, because the Dewalt does not use efficient use of space with all those indentions inside of it even with the grooves cut out.

With my bike, taller is likely better, because of my upright seating, a tall box or tail would more likely help reduce drag, since, even if I tuck, I can only partially tuck and can't really lay my body out like on a sport bike. The ideal width for me is questionable. I'm a small person, and the 14" box was just about ideal for my profile, however, the fairing of the bike is a little wider than my body, and so 15" may reduce turbulence better. It's really hard to say. The crate I've got on there now is close to 15, and I've been getting upper 70s for commuting and around 80 for long, slow rides in hot weather. Length is also questionable, but could be studied mathematically for each of our bikes. The length of a tail for lowest drag depends on the length of the nose and/or total length of the bike, which is why a super-long tail may actually create more turbulence unless a longer nose is also put on a bike. This probably explains why Scott's does so well at increasing his mpg even though it doesn't continue the angle all the way to a point. Doing so would have likely hurt his drag as compared to what he built. Whether or not he calculated this or got lucky, I'm not sure.

Tony Foale Designs, article on motorcycle aerodynamics.
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Old 08-26-2016, 10:04 AM   #7 (permalink)
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Did the overlay tool, looks like there's some promise here (unless I did the overlay wrong, which is possible)
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Old 08-26-2016, 06:11 PM   #8 (permalink)
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That's beyond my expertise, but it looks good to me!

I wouldn't have thought yours was even close to being too long, but you wouldn't want a long tail like Vic or Alan has unless you also had an extended nose. I think that's what the article is saying, and so, if I'm understanding right, it's best just to cut it off flat like Sendler has done rather than to continue the taper to a point.

I'm going to try and learn a little more and eventually come up with some sort of tapered box or tail myself. If I end up not building a box or tail, I'll be looking in to your cheaper/better box than the Dewalt box for mine for the FE Challenge next year

Last edited by gregsfc; 08-26-2016 at 06:23 PM..
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Old 08-28-2016, 03:23 PM   #9 (permalink)
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There are a number of ways to smooth the air flow behind the rider. The key dimensions are the rider's shoulder width and back angle. On my bicycle my shoulders are 20 inches wide and my hips are 17 inches. My back angle is 60 degrees from horizontal. For good stability in all winds, testing done by the Specialized bike company for their aero tubing found a 5 to 1 aspect ratio foil trimmed to a Kamm length of 75 % of the original to be optimum for their road racing bike. So I would shape a body (5 x 20 inches = 100 inches) with the tail cut off at 75 inches from the nose. The tail box would fit tight behind the rider from the shoulders to the seat. The top of the box could taper down about 4 degrees. Two bulkheads and the base plate could be cut from 3/8" aluminum honeycomb or plywood and the skin from a couple wastebaskets or sheet ABS.

Last edited by Grant-53; 08-28-2016 at 03:32 PM..
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Old 08-28-2016, 05:08 PM   #10 (permalink)
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Thanks Grank-53.

I'll have to study, re read, and study your post a few times, as my mind doesn't easily comprehend such detail in mathematics and physics, but I will learn how to do this and give it a go for constructing one, and then that will be the next problem, as I'm not the best at constructing either.

I promise you though, I do have some strengths that counter my weaknesses, as we all do. This sort of stuff interests me a great deal, it's just that I'm not very good at executing it.

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cargo, cbr250r, honda, panniers, top box

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