Upcoming mods: partial streamlining - Honda CBR250R Forum : Honda CBR 250 Forums
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post #1 of 18 Old 11-07-2017, 02:44 PM Thread Starter
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Upcoming mods: partial streamlining

Now that I've started modifying my cbr with raising the gearing and adding a fully enclosed front fender my next steps will be 1) adding and an "aerotrunk, 2) an aero-windscreen and and 3) rear wheel discs. After testing those modifications I'll go to full streamling with a Vetter dustbin nose and long tailsection.
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post #2 of 18 Old 11-07-2017, 06:58 PM
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When are you planning on taking it to Bonneville?
I hope you're talking about "rear wheel BRAKE discs" and not thinking about covering the entire rear wheel with a disc cover like time trial bicyclists do. That is absolutely not suitable for street riding and can be extremely dangerous in any kind of cross wind.
But hey, if you're just planning on becoming a modern Burt Monroe on the salt flats, then more power to you.
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post #3 of 18 Old 11-08-2017, 10:08 AM
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When are you planning on taking it to Bonneville?
I hope you're talking about "rear wheel BRAKE discs" and not thinking about covering the entire rear wheel with a disc cover like time trial bicyclists do. That is absolutely not suitable for street riding and can be extremely dangerous in any kind of cross wind.
But hey, if you're just planning on becoming a modern Burt Monroe on the salt flats, then more power to you.
I don't think that's much of an issue on the rear. With all of the bodywork going on eventually the added area from the discs isn't going to be significant.

This year at Bonneville the crosswinds were a huge problem.

On the front it could be more of an issue, but Vic has run a Ninja with a covered front wheel for quite a while now.
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post #4 of 18 Old 11-08-2017, 08:23 PM
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To each his own. It's certainly not something I'd be keen on doing, but then streamlining my CBR is not something I've given a lot of consideration to. I do know that after riding mostly naked bikes most of my life that I was rather unpleasantly surprised at the very noticeable effect a strong crosswind had on my faired CBR the first time I encountered one Surprised because the pronounced effect of the crosswind seemed way out of proportion to the small fairings the CBR has in comparison to an unfaired naked. I'm sure the light weight of the bike has a lot to do with it, but it was and continues to be an unsettling experience every time I ride on a day when strong wind gusts are forecast.
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post #5 of 18 Old 11-13-2017, 01:50 PM Thread Starter
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When are you planning on taking it to Bonneville?
I hope you're talking about "rear wheel BRAKE discs" and not thinking about covering the entire rear wheel with a disc cover like time trial bicyclists do. That is absolutely not suitable for street riding and can be extremely dangerous in any kind of cross wind.
But hey, if you're just planning on becoming a modern Burt Monroe on the salt flats, then more power to you.
No plans on Bonneville unless there is another Vetter Challenge there. I've ridden thousands of miles using rear wheel discs and other aerodynamic enhancements without putting myself in danger and will continue to do so.

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post #6 of 18 Old 11-13-2017, 02:18 PM Thread Starter
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To each his own. It's certainly not something I'd be keen on doing, but then streamlining my CBR is not something I've given a lot of consideration to. I do know that after riding mostly naked bikes most of my life that I was rather unpleasantly surprised at the very noticeable effect a strong crosswind had on my faired CBR the first time I encountered one Surprised because the pronounced effect of the crosswind seemed way out of proportion to the small fairings the CBR has in comparison to an unfaired naked. I'm sure the light weight of the bike has a lot to do with it, but it was and continues to be an unsettling experience every time I ride on a day when strong wind gusts are forecast.
The problems I have encountered with side wind effects while riding has usually been when there is an imbalance in the streamlining; for example, only modifying the front end with no mods to the back end. In strong winds while riding a fully streamlined moto the tailsection helps self-correct the wind forces on the front end and stabilizes it. Sudden strong gusts can definitely be felt but the key is not over-react. Very strong winds (over 50mph) are dangerous for streamliners as well as any other vehicle with significant sidewall area. For me, the biggest adjustment is making sure when I park my streamliner is the need to prevent strong winds from blowing it over.

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post #7 of 18 Old 11-13-2017, 06:04 PM
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So what kind of mileage are you getting with the streamlining you've already done?
And how much more do you think you may gain by adding a disc rear wheel?
I've heard of hypemiling in automobiles of course, but it's odd that I've never heard many bike owners trying it.
I imagine that since the CBR gets around 70mpg stock, it would be a good platform to experiment with.
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post #8 of 18 Old 11-15-2017, 11:50 AM Thread Starter
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@TrueFaith, with full streamlining I won the 2017 Vetter Challenge at Mid Ohio with a 235 mpg run. I've had other competitions where I've had 186mpg and 187 mpg results. With a 2005 Kawasaki EX250 with partial streamlining I've gotten a best of 111 mpg and it averages around 90 mpg in regular usage. These results were achieved with motos that in stock configuration could get 71 mpg to 73mpg under optimal conditions. My initial test with the stock CBR has produced 88mpg under optimal conditions. This amazing potential is what moved me to change base motos for my future efforts.
I estimate the wheel discs to produce around a 2 to 4 % reduction in air drag. Small, but every bit adds up.
Hypermiling among motorcyclists is rarer than hypermilers in the automobile drivers' general population. Most riders looks at the ~40 mpg performance of their motos and are satisfied. Most are more interested in maximizing speed, acceleration and handling performance beyond what can be legally and ethically used on public streets. I understand the this attraction, I went through my own racer/squid phases as well. Now I try to apply that same competitiveness and energy into becoming the most efficient and safest rider that I can be. I also try to be an advocate for safe hypermiling and to be helpful to others interested as I have been helped by others. I also want more people to look at motorcycling as a transportation option rather than as a dangerous and inefficient toy. Thank you for your questions and interest!
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post #9 of 18 Old 11-15-2017, 06:53 PM
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Wow. Interesting stuff. I had no idea.
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post #10 of 18 Old 11-22-2017, 01:30 PM Thread Starter
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I installed a long windscreen and have roughed out an aerotrunk. I still need to finish the top of the aerotrunk but I took my CBR on a brief shakedown ride and it feels great! It is passing through the air with noticeable decreased resistance. I still need to change the rear sprocket from 38T to 36T after my first frustrated attempt. After the aerotrunk top and sprocket change I'll do a run on my test loop to evaluate the changes. I may post some interim pictures if there is some interest. I hope you all enjoy a Happy Thanksgiving!

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