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Discussion Starter #1
I find my 400, and I'm sure other 400 riders will find the same thing, strange low pressure areas and equally odd high pressure zones.

I'm 6'2" and sit with a decent posture. I think my bike has a taller windshield as I can't see over it.

There's no aerodynamics that bother me at city/rural road speeds but on the highway at 70/80 mph I feel there's something pushing on my entire back, with the highest pressure on my lower back. When there's a big gust of wind the push on my back is surprising. Burgman bops around a bit also.

There's a substantial low pressure on the front of me which I guess is expected as other full fairing bikes I've ridden do the same.

But the overall buffeting is a real surprise to me. Just for comparison I took out my 125 Honda which weighs all of 225-250lbs. on the highway and it blew around less than the Burgman. My V45 Sabre, same weight as the Burgman, was rock solid, didn't budge in gusts.

My 1983 650 Silverwing with fairing lowers, higher than stock windshield and hard bags and trunk blew around far less than the Burgman.

I guess I'll get used to it. I don't have a choice if I want to continue riding this style bike but it certainly is odd, to me, when compared to my other bikes.

Is there any significant aerodynamic changes from my 2004 to the current model year?
 

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Good morning Ontario!

I have a 650, again with a tall (Ermax) screen and I notice the same "pushing effect".

This depends of course on airspeed - with a curious effect when I leave for work with the sun on my back for a 3 km stretch at 90km/h. It feels as is there is no wind at this speed, and my back roasts in the sunshine even on cold days!

However it would take serious gusts to mess the 650 about, it just stays steady up to 140km/h (never taken it any faster).
 

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Called back pressure and a windshield vent will help

At any speed there is a low pressure zone behind you.
You don't start to feel it until speeds get higher.

If you cannot see over the screen, then I'd get a Clearview with a vent that is the correct height. I don't consider it safe riding with a screen you cannot see over.

But mate - you are tall and just like this Concorde rotating for takeoff, you have a big low pressure zone behind you.


( btw it looks even cooler from inside :D )

It's the reason your back and back of your neck get chilly on a cool day. The wind is curling around you and the screen to fill that low pressure zone.
 

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I felt the same buffeting a few months ago when I got my 400. I switched out to the Givi Airflow and the buffeting has, almost, entirely disappeared. This was a real surprise as I got the Givi simply to be able to direct the air where I wanted it. The decrease in buffeting was a pleasant, and substantial, surprise.

I've never ridden a 650 but I'm sure they are better for stability. For me, however, the 400 seems solid at highway speeds after the Airflow was installed. I really think letting some air flow through, as opposed to over and around has a great stabilizing affect. Both the Clearview mentioned and the Givi Airflow do this.

John
 

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I'm in the minority I guess but I find the standard bike screen absolutely excellent on my 400 for what I need. I ride in all weathers and find it ok, a good all rounder. I too am 6'2" tall. I can easily see over the screen. I'm with MacDoc, you should be able to see over the screen for absolute safety. In bad weather, at night, you'll see what we mean!
 

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Don't forget that you are part of that aerodynamic system so different riders can have different results.

I don't know what screen you have Whallythacker but it sounds massive and it could be upsetting the flow more than usual or setting up a particularly strong vortex

It might sound daft but try dropping your elbows or adding a top box

I don't think the Givi airflow screen should be viewed as letting air through.
Notice that:
the hole is at the top of the screen, not the bottom
the additional screen is curved away from the main screen
the front opening is widest gap, its narrower further in.

What it appears to be doing is accelerating the air that travels between the two screens and gives it a bit of focus. This faster air may act like an extra bit of screen extending beyond the plastic.

Motorcycle aerodynamics are generally rubbish but the B400 front end has been thought out more than most. The OEM screen seems a pretty good shape to me but I found that mine flutters too much so I swapped it for an airflow.
 

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Hmmm not sure what happened to the image but this a dramatic version of OPs problem...
 

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That is a great pic and i see what you mean but aircraft aerodynamics are very different to vehicle aerodynamics.
If your bike begins to work like a wing you are in big trouble.

Having said that, there is some of this going on :p

 

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To answer the original question, yes there are aerodynamic differences between the older and newer model but I've never measured or studied them. Seemingly small changes can have dramatic effects, particularly at speed.

Adding a top box might help the situation. It suggests a breakaway point to the airflow and some of it might take that option instead of curling back onto you. The flow is pretty chaotic back there though so I can't guarantee it.
 

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I'm in the minority I guess but I find the standard bike screen absolutely excellent on my 400 for what I need. I ride in all weathers and find it ok, a good all rounder. I too am 6'2" tall. I can easily see over the screen. I'm with MacDoc, you should be able to see over the screen for absolute safety. In bad weather, at night, you'll see what we mean!
Not ride 400, do ride 650, not in minority, find the 650 OEM windscreen perfect also.

People quickly forget what it like to ride bike with no windscreen or small windscreen.
 

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hat is a great pic and i see what you mean but aircraft aerodynamics are very different to vehicle aerodynamics.
If your bike begins to work like a wing you are in big trouble.
The principles are exactly the same.
The low pressure zone behind the wing on the Concord provides lift and in the case of the Burgman rider atrracts the wind deflected by the windscreen around the rider and onto his back and neck.

What you show is a wingtip vortex which is a very different phenomema - you run into the same thing off the rear corner of a truck - especailly those with double trailers.

BTW "working like a wing" can keep you planted in the case of a race car. All these principles of pressure differentials work the same. In the case of an aircraft it provides lift, a race car it provides down pressure, a motorcycle back pressure and a cold neck....at speed it feels like somone pushing you forward.

Here is a visual

 

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You are absolutely right Macdoc. I didn't express myself well.
When I said "a bit of this is happening" I meant there are numerous vortices being produced by the bike, some useful, some not - and it was an excuse to show a dramatic picture while we were talking about wings :)

I do understand what the problem is - I'm a designer, studied aerodynamics in university, served my time in wind tunnels, worked on automotive early but now mostly aeronautics. Not trying to start a spitting contest, just saying this is familiar territory for me too.

The principles might be the same but the application isn't.

While I understand that cars have wings and that lift can operate up down or sideways - you don't want your bike screen to generate lift over your front wheel. It causes extra excitement that you don't need.

In terms of a solution, it might be possible to produce a Kamm Tail effect by adding a wide top box (centre of pressure and stability issues not withstanding)

Or, use a smaller screen and take the flow in the chest so that your head is out of the turbulent boundary flow.
 

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Consider stand-offs to move the windshield up and forward, allowing more airflow under the bottom edge. This would relieve some of the low pressure behind the windscreen, but at the cost of a bit of weather protection.

Combine that with cutting it down so the top edge stays just below eye level.

A cut-down (to fly-screen height) windshield gets rid of the push-forward effect and buffeting, but raises wind noise.
 

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Discussion Starter #14 (Edited)
Oops. Should have mentioned I have a top box, Givi, holds one full face as to size.

Any reason I can't take my trusty hole cutter and cut a 2-3" hole either size of the windshield and add a couple of the these vents? Would they reduce the low pressure behind the windshield?

Ok, my graphic is not showing for some reason but it's a 3" AC vent with adjustable vanes designed for a universal installation.

I will be cutting my windshield down a few inches but I did really like the running with my visor open and having no worry of dust, stones or bugs. I guess if I cut the windshield to just below my line of vision I'll still get a lot of the benefits of it?
 

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Oops. Should have mentioned I have a top box, Givi, holds one full face as to size.

Any reason I can't take my trusty hole cutter and cut a 2-3" hole either size of the windshield and add a couple of the these vents? Would they reduce the low pressure behind the windshield?

Ok, my graphic is not showing for some reason but it's a 3" AC vent with adjustable vanes designed for a universal installation.

I will be cutting my windshield down a few inches but I did really like the running with my visor open and having no worry of dust, stones or bugs. I guess if I cut the windshield to just below my line of vision I'll still get a lot of the benefits of it?
NO reason you can't use the hole saw to make a couple of holes in the windshield to install vents. I used a spade wood bit to put 1" holes in mine. Just go easy and don't try to force the saw.

Even with the windshield cut just below your line of vision most of the wind and the stuff in it will be directed up over the top of your helmet.
 

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Extra holes might alter the flow enough. You can always block it off again if it causes noises or other weirdness.

The screen should already be vented via the bodywork, is the hole between the screen and the headlight clear?

Do you feel drawn forward by your whole torso and helmet or is it more like a hand at one particular place on you back?
 

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I'm in the minority I guess but I find the standard bike screen absolutely excellent on my 400 for what I need. I ride in all weathers and find it ok, a good all rounder. I too am 6'2" tall. I can easily see over the screen. I'm with MacDoc, you should be able to see over the screen for absolute safety. In bad weather, at night, you'll see what we mean!
I too like the stock windscreen.
I do notice that My ride position will effect the buffeting a lot. If I lean forward, lean back, sit up straight, slouch down, etc. they all have a different dynamic effect on the buffeting.

Lucky for me i have found my comfortable sweet spot!
 

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Discussion Starter #18
Extra holes might alter the flow enough. You can always block it off again if it causes noises or other weirdness.

The screen should already be vented via the bodywork, is the hole between the screen and the headlight clear?

Do you feel drawn forward by your whole torso and helmet or is it more like a hand at one particular place on you back?
It can be both. I can be riding with no noticeable push then the road turns differently into the wind then it can be the whole body push. When I get the hand it's generally in my lower back area or my neck.

I'll tell you guys, I've had many fully faired bikes over the years and the Burgman certainly gives me the most interesting ride.

I haven't tried it with a passenger yet.
 

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I too like the stock windscreen.
I do notice that My ride position will effect the buffeting a lot. If I lean forward, lean back, sit up straight, slouch down, etc. they all have a different dynamic effect on the buffeting.

Lucky for me i have found my comfortable sweet spot!
+1. The stock screen on both the 400 & 650 are quite functional and comfortable for me. There a bit of buffeting and wind noise so as not to completely remove the rider from the riding experience.
 

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I added a laminar lip mod to my windshield as per LeDude's article and it made a tremendous difference in turbulence reduction for me. I have a standard 650 and the stock windshield in my case was too short so I was getting a fair amount of wind hitting me just about in the middle of my face shield. A buddy of mine (Ken), has a 06 650 with a GIVI Windshield mounted on his bike and he has the low pressure syndrome on his bike as well. When I had him ride my bike to experience the Rostra Cruise control I had installed, he commented how much he liked my modded windshield. Windshields though as a rule are going to work differently for everyone because everyone is different in stature and size, so there will never be a perfect universal windshield IMHO.

Greg
 
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