The Yamaha Road Star Warrior Forum

overheadcam427:

This may be an aerodynamic phenomena causing the wobble such as Karman vortices shedding off the windscreen.  You should try experimenting to see if you can narrow it down.  Try removing the windscreen or maybe changing it's angle of attack to see if goes away.  You don't need a wind tunnel but you can try using small tufts to visualize the flow in certain areas.  Most of the flow around a motorcycle is probably turbulent, so analyzing tufts will be difficult. 

Believe it or not, I read about the Karman vortices and actually understood a little. The idea of the alternating vortices and their reaching a critical intensity at a certain speed seems to match what I was feeling. I'm going to try some different attack angles and maybe a home-made version of the "Laminar Lip" that I've seen mentioned elsewhere on this forum. I am also going to put a horizontal aluminum strip across the widest part of the windshield to keep it from deforming. This is very interesting!

BTW - engineer at Pax River?

Yes the shield maybe the problem.

I had a Memphis shade it would do that anytime I was going fast or had high pressure on the shield, ie passing a simi.   I added a little more rake to it by milling the top mount back. It fixed the issue.   I went to a clearview shield never had a problem with it.

I did Notice after a while I got the same shakes on my clearview shield.  I deceide to look the bike over very closely  before changing any rake on the shield because it has never done that before.

After a extended flight check I notice my front tire was cupping.  I replaced the tire. The issue went away.

Moral to story is  maybe the shield or could be another issue.

Tire, psi of tire,  maybe the belt tension for your drive belt.

There may be something to the Car tire, not in causing the wobble but in making it more noticable.  I've had my Rocket III to 140 with the CT and it is rock steady, but after a few thousand more miles I started to notice a wobble that got progressivly worse as the speed increased.  I posted about it on one of the Rocket forums and had a response to check out the front tire for wear.  Did that and it looked fine, but for shirts and giggles I remounted my spare wheel with a regular Metzler on it and the wobble was gone.  Hmmmm, I really liked the idea of running on the darkside so I did some more looking, digging and asking around.  And decided that buying a new front tire was worth a shot, so I did that and remounted the wheel with the CT again and so far after about 10,000 miles the front end is rock steady. 

The way that it was explained to me was that a slight wobble in the front end is usually transmitted through the entire bike so it normally goes un-noticed.  But with the CT it gets to the rear end and can't force that rubber rolling pin to shift so it travels back to the front and dissapates through the bars.  The whole path of least resistance thing. 

But in my opinion on your wobble Mike, the windshield is causing it.

Going to change a few things this weekend, one at time, until I can get a handle on this. I love problems like this!

Proposed changes:

A. windshield rake

B. aluminum flatbar re-enforcment of windshield

C. reshape trailing edge of windshield

D. fab a "laminar lip" for windshield (plan to do this anyway to move airstream over my head)

Mustfire:

Proposed changes:

A. windshield rake

B. aluminum flatbar re-enforcment of windshield

C. reshape trailing edge of windshield

D. fab a "laminar lip" for windshield (plan to do this anyway to move airstream over my head)

The first test should be:

A: Remove windshield, see if problem continues.

B: Replace rear tire if problem continues after procedure (A:)

Haha!

siradude:

The first test should be:

A: Remove windshield, see if problem continues.

B: Replace rear tire if problem continues after procedure (A:)

 One other thing to check is your preload on the front end.  When I put the mini-fairing on mine, I put the preload all the way to the down.  My front end just didn't feel quite right at highway speeds (we run fast in ATL).  I have also adjusted the rear shock for the American sized man and not the Japanese kid sized man.  I have had another member ride my bike and he told me that it was stiff, but felt good without all the dipping and squatting a stock bike does.  I'd put my money on the windshield as being the issue.

siradude:

Mustfire:

Proposed changes:

A. windshield rake

B. aluminum flatbar re-enforcment of windshield

C. reshape trailing edge of windshield

D. fab a "laminar lip" for windshield (plan to do this anyway to move airstream over my head)

The first test should be:

A: Remove windshield, see if problem continues.

B: Replace rear tire if problem continues after procedure (A:)

Another non-believer! The tire's fine. I tilted the windshield back a few degrees, problem solved! I'm still going to try the laminar lip.