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sendler · 07-30-2017, 11:51 PM

Much discussion and reasearch has been done regarding sidewinds and streamliners if I can find some of the pertinent threads. Keep in mind that it is only a side wind when you are parked. When traveling on the highway, a 20 mph side wind combines with the 60 mph headwind to appear as one wind vector coming at an angle just off the nose. Which means your airfoil has an angle of attack to make lift if you have good attachment.
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Motorcycles automatically lean into sidewinds due to the trail in the steering geometry if nothing else gets in the way.
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Honda CBR250R Forum : Honda CBR 250 Forums - View Single Post - Cross Winds
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I read and interesting test by some HPV designers who tied a string to a bike in various places to to ride along next to it in another vehicle to try to pull it to the side. Pulling against the rear rack was easiest to pull it over. Pulling against the seat post was second easiest. pulling against the head tube was very difficult to upset the bike since it automatically leaned away from the pulling.
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The maximum lift (side) from a streamlined faring needs to be no further back than the the head tube. A bike is not a dart in the air. It has two wheels hooked to the ground. And it doesn't turn from steering. It turns from counter steering and then leaning. So the idea of a long tail acting through the rear wheel like a fulcrum (or the cg) and turning the nose into the wind is flawed since this would create a counter steering force through the front wheel that is hooked to the ground that would initiate the bike to counter steer, lean, and turn the wrong way. WITH the wind.
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I have ridden behind the Vetter bikes many times and the tail seems to be a non issue either way. Their bikes respond to cross winds about the same as mine. Which is about the same as stock. Although there is no debating the fact that a full tail is more aero than a truncated one and they do seem more imune to shaking in the dirty air of truck wakes.
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Venting across the design at the point of max lift has been the key. Craig tried a door on his bike and took it off because of poor crosswind performance. Judging by the air rushing across my legs on my PCX in crosswinds I would say it takes circa 2 sq. ft. of area.
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Foilers. You will notice that all of the modern sport bikes tend to have a sharp point protruding on either side of the headlight. It is areo when head on. but will spoil the far side attachment in a side wind.
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07-30-2017, 11:51 PM	#7 (permalink)
sendler Master EcoModder Join Date: May 2011 Location: Syracuse, NY USA Posts: 2,935 Honda CBR250R FI Single - '11 Honda CBR250R 90 day: 105.14 mpg (US) 2001 Honda Insight stick - '01 Honda Insight manual 90 day: 60.68 mpg (US) 2009 Honda Fit auto - '09 Honda Fit Auto 90 day: 38.51 mpg (US) PCX153 - '13 Honda PCX150 90 day: 104.48 mpg (US) 2015 Yamaha R3 - '15 Yamaha R3 90 day: 80.94 mpg (US) Ninja650 - '19 Kawasaki Ninja 650 90 day: 72.57 mpg (US) Thanks: 326 Thanked 1,315 Times in 968 Posts	Much discussion and reasearch has been done regarding sidewinds and streamliners if I can find some of the pertinent threads. Keep in mind that it is only a side wind when you are parked. When traveling on the highway, a 20 mph side wind combines with the 60 mph headwind to appear as one wind vector coming at an angle just off the nose. Which means your airfoil has an angle of attack to make lift if you have good attachment. . . . . Motorcycles automatically lean into sidewinds due to the trail in the steering geometry if nothing else gets in the way. . Honda CBR250R Forum : Honda CBR 250 Forums - View Single Post - Cross Winds . I read and interesting test by some HPV designers who tied a string to a bike in various places to to ride along next to it in another vehicle to try to pull it to the side. Pulling against the rear rack was easiest to pull it over. Pulling against the seat post was second easiest. pulling against the head tube was very difficult to upset the bike since it automatically leaned away from the pulling. . The maximum lift (side) from a streamlined faring needs to be no further back than the the head tube. A bike is not a dart in the air. It has two wheels hooked to the ground. And it doesn't turn from steering. It turns from counter steering and then leaning. So the idea of a long tail acting through the rear wheel like a fulcrum (or the cg) and turning the nose into the wind is flawed since this would create a counter steering force through the front wheel that is hooked to the ground that would initiate the bike to counter steer, lean, and turn the wrong way. WITH the wind. . I have ridden behind the Vetter bikes many times and the tail seems to be a non issue either way. Their bikes respond to cross winds about the same as mine. Which is about the same as stock. Although there is no debating the fact that a full tail is more aero than a truncated one and they do seem more imune to shaking in the dirty air of truck wakes. . Venting across the design at the point of max lift has been the key. Craig tried a door on his bike and took it off because of poor crosswind performance. Judging by the air rushing across my legs on my PCX in crosswinds I would say it takes circa 2 sq. ft. of area. . Foilers. You will notice that all of the modern sport bikes tend to have a sharp point protruding on either side of the headlight. It is areo when head on. but will spoil the far side attachment in a side wind. . . . . .