My silly windshield

[BigNorm]

I modified my shield a ways back and had refrained from posting it because it's ugly as hell. I made a 21" shield out of 1/4" plexiglass. I was still getting some head buffetting so I added another additional adjustable shield on top of my thick ass shield. It works well... until late around 90+ MPhil. At that point for some reason the bike begins to weave side to side. The weaving stops when I slow below 90mph. Any of you rocket scientist have any idea why this might be happening and any adjustments I might try to get it to work better. I don't usually ride that fast and stupid but it would be nice to have a way to fix it. Your knowledgeable input is appreciated.

 

[Idaho Red Rocket 3]

I had that weaving for a time too Norm. Turned out to be tire air pressure. Make sure your tires are aired up to the same PSI front and back at about 38 to 40. Doing that cured my weaving.

 

[scot in exile]

Have to repeat what you said that is one ugly windshield, now I never use a windshield but that one is as ugly as the Rocket so I could be tempted.
Remove the windshield get the bike up to 90plus and see if the side to side weave is gone.

 

[Ishrub]

Do any parts of your screen and ahem LIP flex, shudder or flutter at that 90mph or approaching it? That is a very deep secondary screen or lip and a big distance between your main screen and the lip as well, both of which may reduce the laminar flow effect and cause air turbulence or uneven distribution and or pulsing of air flow as the lip may be acting as a screen itself rather than a laminar lip. i.e. The airflow is being pushed by the front of the lip rather than forming a laminar air flow up the back surface of the lip so that it emerges above your main screen and smooths or reduces the air flow behind the screen where your head is. The idea is the pushed up laminar flow prevents air rushing into the low pressure area behind your main screen. There would be a pretty big wind load on the single mount too with that size of lip.

If it was mine I would reduce the mounted height and depth of the lip by cutting the bottom portion off about in line with the current mounting hole and drill another one or three holes to experiment different mounting heights so the top edge of the lip is lower than the main screen top edge. It would also be worth putting two or three more holes in the main screen to give an even bigger range of mount heights. The third link below suggests having the lip top edge higher than the main screen top edge but with at least half the lip depth below the screen top edge to allow a laminar flow to occur. It also states that some may benefit by having the lip top edge below the screen top edge. You could then adjust the lip top edge height down to below the screen top edge in stages and see if it affects the issues you are experiencing. The benefit is you may even get a big improvement below 90mph. I would also try adjusting the angle of the lip in relation to the screen by tilting it forward so the lip top edge is further from the screen than the lip bottom edge

Some basic explanations of the effect being sought.

Laminar LIP Review - webBikeWorld

Laminar Lips

http://www.laminarlip.com/proddc.php

http://www.laminarlip.com/whyneed.php

 

[RKTNMYPKT]

At that point for some reason the bike begins to weave

My Indian weaves baskets

 

[Ishrub]

My Indian weaves baskets

 

[Bob R]

My Indian weaves baskets

Let me know when it starts to weave blankets, you may be on to a roadside income opportunity.

Spy cam pic of @RKTNMYPKT >>>>>>>>>>>>>>>>>



bob

 

[TRIIICK]

Just curious, have you tried going over 90 MPH without the added accessory...??

 

[BigNorm]

Just curious, have you tried going over 90 MPH without the added accessory...??

Yes. It is fine without the shield.

 

[Bob R]

Sounds like the air is spilling off of one side more than the other and when that happens the pressure on the other side is putting more force on the bars. I guess there is a reason wind tunnel testing or at least computer modeling is used for these things. Does it always fall off to one side the first time it starts the wobble?

bob