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Discussion Starter · #1 ·
Hey guys, I've got the factory tall windscreen but just wondering if there is a reason for the standoff between the windshield and the motorbikes body. It is absolutely horrid in the rain as the water flows up under the windshield, drips all over the dash and then beelines it to your crotch area. Is it purely cosmetic or does it do something strange aerodynamically if there isn't a gap? My old bikes didn't have any gap FWIW. Anyone plug it up with some rubber foam to good effect?
 

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I don't know the actual reason but your own experience shows that it is a poor design. Does this design carry over into the more expensive models? My best guess is it's simply more cost effective but I could be wrong.
 

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The gap isn't a cost measure, nor poor design.

In the case the windscreen is sealed off without the gap underneath, air will roll over the screen and create a buffeting effect, as behind the windscreen is essentially a vacuum of semi stagnant air in this scenario, so as air flows over the top it will roll off into the cockpit and creates this buffeting effect, which will likely result in it being louder, as well as greater drag.

With the air gap underneath, it eliminates the stagnant air behind the screen and will flow in line with the air above, hence sending it over the rider, or at least higher up to prevent the aforementioned negatives.

A lot of high end modern sportbikes run the same thing, though in different spots to create the same effect. Can't explain or understand some of them unless you see the wind tunnel stuffs.

You can also achieve similar results with greater frontal area (think cruisers), however this is a sports bike, where aero and minimal frontal area is ideal.

Hard to explain, though hopefully this helps.


Edit:
Just found this photo which may help to visualise what I'm talking about.
14727
 

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Well, based on the OP's description I would have to say this is a poorly designed feature on the 400 and the reason why it is poorly designed is because of cost. I am not seeing the windscreen gap on other models, can you share some pics of other bikes with the same screen gap?

You are confusing function and design. I get the air flow issue but that is more of an excuse rather than an explanation for why the Ninja 400 is designed in such a way that it allows for a very unpleasant experience. Other more expensive models appear to have a much more thoughtful approach.

And personally, I prefer a solid to body windscreen regardless of those fancy drawings :) because of the same reasons as the OP. I have never given a second thought about wind turbulence but a wet dick and water on my instrument cluster/inner windshield will surely get my attention.

The first time I noticed the gap I had a WTF Kawasaki moment myself.

It is absolutely horrid in the rain as the water flows up under the windshield, drips all over the dash and then beelines it to your crotch area.

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Discussion Starter · #7 ·
The gap isn't a cost measure, nor poor design.

In the case the windscreen is sealed off without the gap underneath, air will roll over the screen and create a buffeting effect, as behind the windscreen is essentially a vacuum of semi stagnant air in this scenario, so as air flows over the top it will roll off into the cockpit and creates this buffeting effect, which will likely result in it being louder, as well as greater drag.

With the air gap underneath, it eliminates the stagnant air behind the screen and will flow in line with the air above, hence sending it over the rider, or at least higher up to prevent the aforementioned negatives.

A lot of high end modern sportbikes run the same thing, though in different spots to create the same effect. Can't explain or understand some of them unless you see the wind tunnel stuffs.

You can also achieve similar results with greater frontal area (think cruisers), however this is a sports bike, where aero and minimal frontal area is ideal.

Hard to explain, though hopefully this helps.


Edit:
Just found this photo which may help to visualise what I'm talking about.
View attachment 14727
Ah ha, yes that makes sense in terms of air flow. Similar to a F1 front wing with the multiple planes being split and staggered to help clean the air flow up.
 

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Discussion Starter · #8 ·
Well, based on the OP's description I would have to say this is a poorly designed feature on the 400 and the reason why it is poorly designed is because of cost. I am not seeing the windscreen gap on other models, can you share some pics of other bikes with the same screen gap?

You are confusing function and design. I get the air flow issue but that is more of an excuse rather than an explanation for why the Ninja 400 is designed in such a way that it allows for a very unpleasant experience. Other more expensive models appear to have a much more thoughtful approach.

And personally, I prefer a solid to body windscreen regardless of those fancy drawings :) because of the same reasons as the OP. I have never given a second thought about wind turbulence but a wet dick and water on my instrument cluster/inner windshield will surely get my attention.

The first time I noticed the gap I had a WTF Kawasaki moment myself.

It is absolutely horrid in the rain as the water flows up under the windshield, drips all over the dash and then beelines it to your crotch area.

View attachment 14728
Haha what's worse is that at highway speeds the airflow coming up from the front wheel well blows it all over the place as well. I am very tempted to seal it with some thick foam. I'll let you know any adverse effects. If you don't hear back then don't try it 😂😂😂
 

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I've always wondered about that as well and never cared for the gap, which is still present even with most race bodywork brands. I doubt it's for aerodynamics otherwise every MotoGP, Moto 2 and Moto 3 bike would have that, since those bikes are designed to optimize aerodynamics as much as possible.
 

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can you share some pics of other bikes with the same screen gap?
ZX6R has the same gap just above the ram air port. Same function.

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H2 has it too.
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ZX10-R has it as well, though in a different way.


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Sure, it may not be as pretty as other models, however it does have a function.
You've got to remember, this is a budget entry level sportbike we're talking about and making the windscreen seperate from the fairing with the same function, whilst (presumably) keeping costs down during production for Kawasaki.
I'd complain if it was a $15k+ bike, though taking it for what it is, it's impressive they bothered this much.
 

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Marquez's bike. World champion. Not as drastic, though still there. Same idea.

View attachment 14752
Ok...but that's one. I'm not seeing it on any other bikes and I've been looking at pics online for the past 20 minutes lol Plus those on MM93's bike look to be pretty insignificant for aerodynamics. I remember back in like 2013 the Ducati guys drilled a bunch of holes on their GP bikes on the edges of the windscreen and front fairing. I think they did it at Phillip Island and supposedly because it was very windy. After that other teams played around with that and tested it but most said it made no difference, and I haven't seen any bikes with holes or slots in the front for quite some time...until you posted this pic of Marquez's bike. That could be more for anti-fogging maybe...🤷‍♂️
 

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Ok...but that's one. I'm not seeing it on any other bikes and I've been looking at pics online for the past 20 minutes lol Plus those on MM93's bike look to be pretty insignificant for aerodynamics. I remember back in like 2013 the Ducati guys drilled a bunch of holes on their GP bikes on the edges of the windscreen and front fairing. I think they did it at Phillip Island and supposedly because it was very windy. After that other teams played around with that and tested it but most said it made no difference, and I haven't seen any bikes with holes or slots in the front for quite some time...until you posted this pic of Marquez's bike. That could be more for anti-fogging maybe...🤷‍♂️
Road bike VS race bike. It's off topic to the original discussion about the 400. I'm not the head of aerodynamics in a MotoGP team, just my 2 cents. However it may not be as essential on a race bike as majority of the time they're behind the fairing, at least at speed. Wouldn't be as important through the corners even with that effect.
They'd be filling that stagnant air and become part of the aero. Guess it reduces that problem of the air dipping over the screen if the rider's in that area. Though your guess of anti-fogging is just as likely in the case of race bikes.
 

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The 2020 ZX10 doesn't appear to have any gap and the ZX6 looks like it has a very small gap. Also, Yamaha, Honda, Suzuki do not have any gaps so this appears to be more of a Kawasaki design feature and not an industry wide design.

There is a massive difference in gap on the Ninja 400 vs the ZX6. So my point was the 400 gap is the result of cost savings and therefore is poor design. If it was a great design the ZX6, ZX10 (and all manufacturers) would have the same hideous gap with the same unpleasant consequences but that is not the case.

2020 ZX10 (solid to body windscreen, no gap present)

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2020 ZX6 appears to have a very small gap. I don't think this small of a gap would have any real impact on wind turbulence over the top but I am not an engineer so just a guess. Also, I would expect a lot less water under the windscreen on the ZX6.

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The 2020 ZX10 doesn't appear to have any gap and the ZX6 looks like it has a very small gap. Also, Yamaha, Honda, Suzuki do not have any gaps so this appears to be more of a Kawasaki design feature and not an industry wide design.

There is a massive difference in gap on the Ninja 400 vs the ZX6. So my point was the 400 gap is the result of cost savings and therefore is poor design. If it was a great design the ZX6, ZX10 (and all manufacturers) would have the same hideous gap with the same unpleasant consequences but that is not the case.

2020 ZX10 (solid to body windscreen, no gap present)

View attachment 14754 View attachment 14755

2020 ZX6 appears to have a very small gap. I don't think this small of a gap would have any real impact on wind turbulence over the top but I am not an engineer so just a guess. Also, I would expect a lot less water under the windscreen on the ZX6.

View attachment 14757
The top pic has gaps either side, toward the top of the screen.

I seriously doubt there'd be cost saving either way.

I have to say I do get more of a turbulence effect acting on my head at speed on my MC22 than the Ninja while in a 3/4 tuck.
The intention seems to be for the rider, not top speed aerodynamic advantage.
 

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Road bike VS race bike. It's off topic to the original discussion about the 400. I'm not the head of aerodynamics in a MotoGP team, just my 2 cents. However it may not be as essential on a race bike as majority of the time they're behind the fairing, at least at speed. Wouldn't be as important through the corners even with that effect.
They'd be filling that stagnant air and become part of the aero. Guess it reduces that problem of the air dipping over the screen if the rider's in that area. Though your guess of anti-fogging is just as likely in the case of race bikes.
My point was that if it really was made to streamline the aerodynamics of the bike, then all race bikes would have it too. I'm not sure what you mean by stagnant air. There is no stagnant air as the bike is moving. The air generally flows from the windscreen above the rider's helmet (if you're in a tucked position). The diagram you posted before is not realistic because there's no rider on the bike, so there wouldn't be any turbulent air behind the windscreen. Now in a street riding situation where the rider is sitting upright, aerodynamics pretty much go out the window at that point because all that air is going to hit you right in the face and torso area, so I don't see how a gap below the windscreen would make any difference anyway.

We might all be overthinking this and maybe they just did it for styling, and there is no real scientific reason for it at all lol Maybe someone at Kawasaki thought it looks cool so they did it lol
 

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Yeah I think he means turbulence, or a vortex similar to the theory that driving with the tail gate down in a truck created better mpg, when mythbusters and some others actually proved the way the airflow went over the truck and created a negative space, or a vortex, in that area actually helped, and there was not enough air to increase coefficient drag to the point the tail gate up acted like a vehicle shaped like a box rather than a dart...so with that I would think ariflow would create a vortex and smooth it, but create turbulence for the rider? so they have it flow through instead...I don't know I can say the R3 has a much better looking windscreen than the 400. More like a R6 V shaped bubble, or like the 1098 or Ducati Panigale...makes the front look more aggressive and fast.......the 400 windscreen looks more like a touring bike, or adventure bike with the gaped windscreen
 

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My point was that if it really was made to streamline the aerodynamics of the bike, then all race bikes would have it too. I'm not sure what you mean by stagnant air. There is no stagnant air as the bike is moving. The air generally flows from the windscreen above the rider's helmet (if you're in a tucked position). The diagram you posted before is not realistic because there's no rider on the bike, so there wouldn't be any turbulent air behind the windscreen. Now in a street riding situation where the rider is sitting upright, aerodynamics pretty much go out the window at that point because all that air is going to hit you right in the face and torso area, so I don't see how a gap below the windscreen would make any difference anyway.

We might all be overthinking this and maybe they just did it for styling, and there is no real scientific reason for it at all lol Maybe someone at Kawasaki thought it looks cool so they did it lol
Apologies, didn't mean stagnant air so to speak, but moreso that space behind the screen has minimal air movement, at least compared to the rest of the bike at speed, which is why the air dips over and creates turbulance without that gap.

I agree in terms of street riding if you're sitting dead upright, it will be practically useless.
As the rider becomes more streamlined with the bike, in theory will create better laminar flow of air over the rider due to the aforementioned gap, likely to create the best outcome in a 3/4 tuck.
Once again, I agree that in a full tuck it becomes somewhat useless to a degree, as the riders head fills up that negative space and air will, presumably flow over the top.


Although after thinking about the photo I put up of Marquez recently and watching the Czech race, I believe the little slits appear to, at least in my opinion, be there to reduce the turbulance around the riders helmet in a full tuck. As their helmet is dead in the middle & shoulders streamlined with the fairing, the only air space left is either side of the helmet.
Whilst keeping the bike as streamlined as possible, I guess to reduce drag, the slits appear to be used to fill in the gap either side of the helmet in a tucked position to stop the air dipping over either side of the helmet.

Another example, here's Brad Binder from the weekend. Note the windscreen slits:
In fact, they may be just as useful when the rider is not in a streamlined position as pictured to help aid the overall aerodynamics of the bike.

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I think someone needs to cover it up with tape and see if they can tell a difference.
Just taped up the gap and went for a ride.

Same track, four times with the tape and four times without.

For reference:
  • My bike has a + 1 sprocket up front
  • Top speed in this case is limited by the length, angle change and surface of the track, hence making the run up and back twice to find a median for both in the same conditions.
Top speed

With Tape : 188 KPH
Without Tape : 196 KPH

Notes with tape:

<100 KPH - No noticeable change between the two
100-120 KPH - minor wind noise increase, as well as an increase in turbulence around the helmet up to around a 3/4 tuck. No noticeable difference to without tape in a full tuck.
120-190 KPH - Progressively worse turbulence, causing my helmet to shake around a bit - wasn't unrideable, though uncomfortable & louder. Full tuck made a minor improvement; however, turbulence was still evident around either side of the helmet.

Notes without tape:

Air flow around the helmet over 120, up to 200 KPH in a 3/4 to full tuck felt much cleaner. Turbulence was gone (at least felt like it, don't know for sure without a wind tunnel), just the usual wind pressure remained that I'm sure you're all aware of. No helmet shake, much more comfortable.


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