Question NC Windshield Modifications/Additions for reduced wind buffeting

[WestcoastKid]

I think most motorcycle riders have experienced wind buffeting on their helmet to some extent. When wind buffeting is bad it can really take the enjoyment out of riding at least that's my experience. I'm currently using a Givi Touring Screen on my 2022 NC750 along with an adjustable visor (Universal Clamp On Type). It's really made a huge improvement over the stock windshield, but I'm still getting some wind buffeting.

There's a lot of shields available in the motorcycling world that incorporate holes, ports or operable vents designed to counteract the vacuum that causes turbulent air behind the screen. I'm curious if anyone has been brave enough to add holes, ports or vents to their windshield and found it made a noticeable improvement?

 

[vinay]

The stock NC750X windscreen has a gap that coincides with the bottom of the upwards channel behind the display. Lots of word but if you go through them one by one I'm sure you'll understand what I mean. This will create a nice upwards draft behind the screen to balance the air flow in front of the screen. The less balance there is, the more vortexes you're going to have at the edges, which is what is going to bother you. There is also a gap at the underside of the windscreen, but a good bit of that air is supposed to flow underneath the display. Why many (but not all) aftermarket windscreen manufacturers choose to forego that hole behind the display is beyond me. Possibly just because Honda produces such huge quantities that they can actually injection mold their screens (which obviously requires an expensive mold) so they can actually make the proper shape around the hole to guide the air. Companies who press-form their screens don't have that much freedom in shape so they may be able to cut holes, but won't be able to create the appropriate shape nearby. So I'd expect that if it would be as simple as creating holes in a screen not designed for it, it would already have been done. Plus of course, I would hate to see my screen shatter whilst riding at speed because a crack starts right from your carefully cut hole!

So yeah, the stock screen has a hole in the best place imaginable. Other screen designers have other approaches (or don't have any and just want your money). Madstad which quite a few people seem to be raving about promotes the airflow behind the screen by shifting the screen even further forwards.

Anyway, I'm surprised to see that you consider your Givi Touring screen with clip-on visor to be a huge improvement over the standard screen with clip-on visor. Because the latter is what I have and even with a peaked helmet I have no issues at all. I've got the clip-on visor a bit in front of the standard screen with a 50% vertical overlap and tilted a bit steeper than the standard screen. The top of the clip-on is about at chest level. No buffeting, no bugs on my helmet visor. Interesting to see that even between quite similar bikes, people have such different experiences!

 

[Rydinon]

I found that Calsci's vent (hole in the middle of the shield) did not have much effect on buffeting on my ST1300. My main problem with it was was water collected on the lip and when the drop was big enough, it would separate and fly up into my face. If my visor was open, the drop smacked me right in the middle of my face. Covering it made no difference. I ordered a Calsci shield for my VStrom w/o the opening. Turbulence seems to be caused by other things - moving the mirrors outward with extenders made a big difference on my VStrom. My NC has a Madsted shield and I love it. Nice and quiet and I look over the plastic.

 

[yojimg]

I also run a Givi and add-on deflector on my 2018. I've added cylindrical plastic spacers about 15mm long underneath the windscreen to increase the air gap to try to help with buffeting. I also had to use longer bolts. Apologies for the blurry photo -- it's a screen grab from a commuting video.



-Jim G

 

[vinay]

I found that Calsci's vent (hole in the middle of the shield) did not have much effect on buffeting on my ST1300. My main problem with it was was water collected on the lip and when the drop was big enough, it would separate and fly up into my face. If my visor was open, the drop smacked me right in the middle of my face. Covering it made no difference. I ordered a Calsci shield for my VStrom w/o the opening. Turbulence seems to be caused by other things - moving the mirrors outward with extenders made a big difference on my VStrom. My NC has a Madsted shield and I love it. Nice and quiet and I look over the plastic.

I looked up these Calsci screens but to me these appear to be press formed screens with holes, but not really a duct/gulley leading up to the hole like the stock NC750X has, does it? If so, I'm not too surprised it doesn't work as well. A flow over a surface is parallel to that surface. It won't suddenly dive into a hole because it is there. In fact, it is actually more likely to suck air from behind the screen (so some of the air that entered from underneath) back to the front. Pretty much the opposite of what you want! As I mentioned in my previous post these aftermarket screen manufacturers produce screen for so many different bikes (and sell only a few of each of them) that it doesn't make sense to invest in the expensive tooling it would take to make these shapes properly. That is, injection molding which requires super smooth and accurate (for optical quality) molding dies for both sides. And obviously especially considering the size of windscreens some of these aftermarket manufacturers are pumping out would considerably increase the costs of the mold! Press forming requires only one product specific die and as the material doesn't complete melt (but only heated up to glass transition temperature) you don't need an equally smooth mold either. Yet as mentioned, apparently it is too difficult to produce these gully's using this technique in which case I'd say, don't make these holes either.

As for turbulence, apparently it is getting a bad rep. Yet really, it isn't so black and white. See, you don't really want a vacuum or even that much of an underpressure behind your screen. Because when that happens, the air that's been pushed aside by your screen will urgently try to dive back down and in to fill the gap. And this is going to bother you. So that's the primary goal, keeping that air from diving back in. Now as for turbulence, this develops over the surface. The boundary layer of air grows and at some point, it trips and becomes turbulent. One way to do that, is to scrape off that boundary layer from below. In my case (so the stock NC750X screen with a spoiler on top) this happens in three places. 1) At the bottom of the screen. This is the air that moves upwards past the headlight and now part is being scraped off. Part flows up along the inside of the windscreen and the rest moves underneath the display after which it expands (hence slows down) 2) Through the gap in the windscreen. Again, this moves up between display and windscreen until it reaches above the display and also expands. 3) Between the windscreen and the spoiler. Because the slightly steeper angle of the spoiler with respect to the windscreen, you again have an expansion of the air that passes. The air that stays in front of the screen remains laminar and moves upwards. What is more, there is enough air moving upwards between windscreen and rider and as this air needs a place (much of it will obviously move sideways) part of it will help push that laminar flow up and over the rider head rather than have this underpressure which sucks it back down and in. So even though this air between rider and screen is turbulent, it is also slow and doesn't really do any harm. On the contrary. Your helmet is a bit of a dome. Now imagine a smooth dome (or cylinder) in a flow. It would create a big wake with laminar flow on both sides. Not only does the wake (underpressure) pull the dome/cylinder back, the laminar flow also tries to fill that gap. And as both sides do so in an oscillating fashion (a bit like how a flag moves in fast winds) the wake direction alternates and so does the resultant force on your head. Turbulent flow dives into the wake much quicker hence reduces the forces on your helmet. See, there may be a bit of a misconception. Many seem to believe wind forces are overpressures from the front, yet in fact it is actually the underpressure in the wake which causes the unbalance and pulls something back. A golfball has dimples for this very reason. To trip the flow from laminar to turbulent to reduce the size (and effect) of the wake hence reduce the resultant forces of a golfball in flight.

So yeah, vortexes around the windscreen edges due to pressure differences are to be avoided but turbulence itself is your friend.

 

[Rydinon]

Given the vast differences in riders (size), I suspect designing a proper windshield for a motorcycle is an exercise in futility. Toss in the cost of actual wind tunnel testing and it is my guess that most of our available windshields are more what the company thought a proper windshield should look like than a product of hard core engineering design and testing. Expecting your windshield to function as we want it to with the other hardware on the bike might not be realistic.

My VStrom's OEM shield did not work for me - it was too noisy. As I said, I put a Calsci on the bike and this too did not eliminate turbulence. I read about and tried wind deflectors* - not much change. Someone else suggested changing the mirrors to Aprilia brand. That made a little difference, and moving them outward on mirror extenders reduced buffeting in my helmet area even more. A shorter or taller rider (not many of the former) might not have had my experience with either the OEM or the Calsci. Let him wear a different helmet and airflow/turbulence might be different.

*These are VStrom specific and are bolted to the faring up front to reduce wind impacting the riders chest.

 

[vinay]

Getting the perfect setup requires extensive testing, but a good concept starts with a qualitative idea of what one wants to achieve. I believe in the concept of peeling off the developing boundary layer and guiding it behind the windscreen preserving and upwards flow and keeping the flow in front of the windscreen clean and laminar. I actually do believe Honda does perform windtunnel testing on their complete NC750X with the standard windscreen. They obviously don't test with the clip-on screen but these screens typically allow for sufficient adjustment to get them do what you want. I've read about enough people putting clip-on screens on top of big aftermarket windscreens. But I'm curious, who has actually installed a clip-on screen on the stock NC750X screen and even with a bit of experimentation didn't get a satisfactory performance. I'm kind of baffled that even with a pretty cheap Givi-lookalike clip-on and a peaked helmet (Airoh Commander) can keep my helmet visor clean from bugs and have no issues with buffeting on body nor helmet. I'm about 6ft tall and ride a bike pretty much similar to what most of you are riding.

 

[dduelin]

Given the vast differences in riders (size), I suspect designing a proper windshield for a motorcycle is an exercise in futility. Toss in the cost of actual wind tunnel testing and it is my guess that most of our available windshields are more what the company thought a proper windshield should look like than a product of hard core engineering design and testing. Expecting your windshield to function as we want it to with the other hardware on the bike might not be realistic.

One thing that the Madstad products have that most other motorcycle windshields do not are large rider adjustments for height and rake. Besides choosing the recommended height the rider then can fine tune the installation for individual preferences. I remember a riding buddy with a VeeStrom that simply bought the adjustable brackets Madstad offered for the stock screen and claimed transformation of the bike for distance riding and touring.

 

[Lee Dodge]

I have a 2020 NC750X with the stock screen. My major issue was more noise than turbulence. There was some turbulence but nothing like the V Strom I used to own. (That thing would vibrate your helmet so much it could blur your vision.) I added a spoiler to the top of the NC screen and tried different heights and angles. None really seemed to make much difference. Then I remembered reading an article from 70's about NASA experimenting with turning vanes on the rear corners square bodied vehicles to push air into the vacuum behind the vehicle. I decided to try angling my spoiler back towards me instead of vertical. The noise reduction was very noticeable. Its not quite as quiet as running without a screen but way better than before. The wind hits me right at the face shield but its smooth and quiet.

 

[vinay]

Ah interesting, so your bike (including the windscreen) is similar to mine. I admit I never thought about the noise or what is considered normal. I'm wearing hearing protection (Alpine Race) and I'm playing a tune over the communication device so noise doesn't bother me too much (nor would I feel any reason to spend money on an aftermarket exhaust for "better" sound). I just always thought it was inherent to driving motorcycles on the highway yet at the same time I don't think it is excessive as it is now. Whether aiming the flow straight at your face may or may not be an issue depending on the shape of the helmet. Rounder helmets may not be that much of an issue but at higher speeds my helmet tends to jank my head if I look sideways. So shifting the flow over my head was more my goal rather than reducing noise.

Out of curiosity, how was the spoiler aimed previously? You mention it was "vertical" but does that imply vertical and on top of the standard screen (nearly closing the forwards gap between the two screens) or did you orient it vertically but indeed in front of the stock screen (so with a good vertical overlap and a fair horizontal gap)?

Other than that, your fender looks nice. Much better rounded at the edges so that should help a good lot compared to how squarely mine was trimmed.

 

[Lee Dodge]

The spoiler is an MRA X-Creen Sport. It is very adjustable. I tried all kinds of orientations including vertical, parallel to the screen, and tipped slightly forward and various heights. They were all pretty much the same until it I tipped it back.

 

[yojimg]

But I'm curious, who has actually installed a clip-on screen on the stock NC750X screen and even with a bit of experimentation didn't get a satisfactory performance.

I have both the stock screen and the previously-shown Givi tall screen for my 2018. I've tried both screens with the clip-on deflector, and ultimately decided that the Givi screen works better for me.

-Jim G

 

[vinay]

Thanks all for the info. Interesting to see there are so many different preferences and experiences. I now also realize I hijacked this thread a little so it is time to hand it back to the OP: what experience do people have with holes in the windscreen?