Author Topic: DIY Special deflector for OEM Touring Screen  (Read 88021 times)

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#176

Offline plukenannabel

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Re: DIY Special deflector for OEM Touring Screen
Reply #176 on: August 19, 2019, 08:09:38 PM
it works, -ish

better but not perfect

#177

Offline AussieKiwi

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Re: DIY Special deflector for OEM Touring Screen
Reply #177 on: June 24, 2020, 05:33:47 PM
On the Africa twin an airdam like this makes a huge difference.

I am creating one that will cover more of the airgap than the OP's version in this thread - will post when done.



Last Edit: June 24, 2020, 05:46:15 PM by AussieKiwi
2012 VFR1200X Cross Tourer
2016 CRF1000 Africa Twin
2008 ABS XL1000V Varadero
1997 XRV 750 Africa Twin

#178

Offline VFR1200XDH

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Re: DIY Special deflector for OEM Touring Screen
Reply #178 on: August 03, 2020, 03:32:18 AM
Just some history regarding air deflectors for the around the forks area.  The airflow coming up from the gap by the fork tubes was identified back in 2000 and possibly eariler as a major contributor to buffeting. The Honda ST1100 suffered from buffeting even though it had airflow holes built into the windscreen. Testing revealed that by blocking some of the air coming up by the fork tubes the buffeting decreased markedly but there was a subtle but annoying side effect, low pressure behind the windscreen. Some of us blocked only a small area while others blocked as much as possible.

At first it wasn't noticeable and the less buffeting was so welcome it was overlooked. After a while though, complaints about the low pressure area surfaced. The effect was very minor but the longer you rode the bike with the deflector in place the more you noticed this low pressure effect. It felt like a slight amount of pressure was pushing you from behind right at shoulder height. There wasn't really any pressure at all, what was happening was that the airflow coming up by the fork tubes was gone and thus less air pressure was pushing against your upper torso. On short rides it wasn't much of a problem and for commuting the reduced buffeting was a decent trade-off but for longer distance riders, the deflectors soon found their way in the experiment bin.

The other effect we noticed was that you started having this feeling like you changed altitude rapidly, a sort of clogged ears thing. When the air flow from in front of your body and helmet is eliminated the buffeting goes away but you also create that low pressure area right where it doesn't need to be.

In the end many of us that went the route of the deflector also went back to the way of adjusting the angle of the windscreen and allowing adjustable airflow to come up on the inside of the windscreen. Craig Vetter did a lot of testing to reduce buffeting and that is why he started putting in adjustable windscreen vents in the Windjammer fairing screens. Since then, Honda followed suit although not with adjustable vents but just holes.

Nowadays with adjustable windscreens, changing the angle of attack can practically eliminate buffeting although often buffeting is caused as much by your helmet as anything else.

There was one additional effect from the deflectors, they stopped the air flow so well that engine temperatures increased in some conditions. By preventing or reducing much of the airflow riding by the fork tubes heat didn't dissipate as was the original intent and a build-up of hot air became a self generating problem. At higher speeds it wasn't an issue but at speeds up to 50 mph it sure was. You didn't feel it but the engine and everything forward and below the rider sure did. Without a place for the heat to go the temps rise, not enough to bother the rider but it can be quite a bit for all the plastics, the fuel tank and associated components.

Just blocking airflow instead of redirecting it can have unintended consequences over a longer term. The airflow, especially up front by the radiator needs some place to go and one of those places is up by the fork tubes. Unlike most cars, there isn't some free space behind the radiator for the air to go so air flowing up by the forks keeps it moving. Once hot air gets trapped in a static area cooling is affected.

We tested the air temps before and after the deflectors were put on and the differences were not small, often 15 or more degree. Factor in a hot day, slower riding or stopped traffic and it can make a bug difference. Heat rises and when it can't it just builds up. You'd think that with some gap not covered it shouldn't matter but measure it and see for yourself. While I haven't testing it on the VFR-X as I don't experience buffeting and it is no ST1100, maybe someone could give it a go?
To V or not to V is not the question.

#179

Offline Marvinjsn

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Re: DIY Special deflector for OEM Touring Screen
Reply #179 on: August 03, 2020, 10:35:30 AM
After I got my CT I had a look at this thread because I too had the buffeting issue, especially at highway speeds. I have the OEM touring screen with flip up on it installed. I found a solution given by the use of spacers. It was posted by member "the mechanic" on October 25, 2015 in the thread "Best touring windscreen".
The following was written by him:

"Yes, you are correct, for part of the problem. The gap between the bottom of the screen and the panel is so small, very little air comes through. This causes a low pressure area directly behind the screen and around the dashboard area. The deflector around the fork area works because it limits the amount of air sucked up into the low pressure area. Another way of sorting this is to put four 5mm spacers under the screen bolts to lift bottom of the screen away, thus letting air bleed through, you can also achieve this by taking the side brackets out and slotting one of the holes to allow the screen to tilt, the only snag with this method is, some sat nav brackets put the sat nav very close to the dashboard anyway, this limits the amount of tilt to play with. The spacer mod, I have done on three bikes of my own and lost count how many others I have done it on, all the owners report an improvement over stock."

Putting spacers behind all 4 the screen attach points as to bring the windshield more forward (away from the bike) for me was the solution to the problem.
It increased the gap between screen and bike and the buffeting is gone, I still have an airflow of course, but not buffeting and disturbed, just a normal airflow as you have riding a bike.
I used spacers of about 8mm thick.

See pictures.





#180

Offline VFR1200XDH

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Re: DIY Special deflector for OEM Touring Screen
Reply #180 on: August 04, 2020, 08:21:09 PM
You got it right and backed up by many people who designed windscreens and fairings over many decades. Madstad created a good business making adjustable windscreen brackets that let the rider adjust among other things, the airflow under the windscreen to reduce the low pressure area. This still lets heat from the radiator and engine rise; without continual airflow up from the forks area everything below there is doing a slow roast. Eventually wire insulation and plastics get brittle and cause problems.

The engineers at motorcycle manufacturers know what they are doing, mostly. If the simple solution to buffeting was to block airflow around the forks, doing it as part of fairing design would be easy and not a cost problem. There is a reason they don't do it and saving money isn't likely the reason. If anything, they'd sell the accessory, none do.

I recommend anyone blocking airflow to check the temps above the deflector or below it. You can feel it with just your hand. Heat builds up and feeds on itself if it doesn't have a place to go.
To V or not to V is not the question.