High Speed WOBBLE OMG not again!!!

[ruger44]

Just made a couple of 1700 mile trips to the smokey mountains on my 93 FXRS-SP. Rode hard and run the curves like a mad man. The bike handles very well in all kinds of curves EXCEPT high SPEED sweepers. (Like on the Interstates)
I was doing around 85-90mph on I-59 north out of Birmingham when I came into a long sweeper and the bike started the Harley wobble....seemed like forever but it came out and I thought it was just a fluke
On my way back I was in a another high sweeper around 75mph when I felt a dip in the highway and BANG it went to crap again this time it was worse and brought me tooooooo close to the car next to me. I was on the inside lane and could see the driver's eyes
watching this bike trying to swap ends at 75mph next to his door

IS this normal for all rubber mounted Harley's my 00 Road King has never wobbled and I have rode it Hard all around the Ozarks.

I did have a wilndshield and a small t bag on the back.

Run Avons 140 rear 19" 110 front.

I checked the fall away and it seams good maybe some one knows a better way to set it (I did it my the HD manual)

I reinstalled the original bushings back when I had the frame Powder Coated and after showing them to a Master HD Tech, he said they were not in need of replacing.

Is this my problem, do I need to go with the newer aftermarket bushings??


HELP
I do not trust the bike now until I can resolve this
Thanks

[plugeye]

is the rake stock?
bike been lowered?
tires worn or cupped?
all wheel bearings good?
wheels in balance?
steering stem too loose?
lots of possible contributors

[lucille]

Do you run with a fork brace?

[Faast Ed]

You were on a trip so I would assume you were loaded down with luggage?
Lot of weight behind the rear axle will encourage this behavior. Tire issues can cause it too. (Simple things first).

[ruger44]

Thanks for the help guys
I run a fork brace and had about 10 lbs on the luggage rack when this happened.
I have a White Brothers kit on the front about 1-1/2 lower
Works shocks on the rear 1-1/2 lower
I checked the fork bearings and they are ok.
I am going to replace the rear isolators with an after market type.
One question I do have what is the correct air pressure for the Avon Venoms I have mounted.
I was running 32psi front and 36psi rear is this too low for these tires on a FXR? I tried a higher pressure but the bike rides very hard on Louisiana roads (they suck)
Again thanks for the help.

[Faast Ed]

32 psi front sounds awfully low for any tire. Good chance that contributed to your problem, in my opinion.

Before I spent money looking for more add-on parts, I'd put some air in there and give it another test ride. Hopefully you don't already have uneven wear because of it.





.

[ruger44]

Faast Ed I believe low pressure was part of the problem I went to 40 front and 42 rear.
After speaking with a local Indy we came to the conclusion that it was a combination of rear weight, windshield and low air pressure.
I am still going to swap out the original rear isolators.
Thanks

[GJarrett]

Originally Posted by ruger44

I did have a windshield....

The cause could be a combination of issues, some of which have already been addressed. Each issue by itself may not be the culprit, but combined they can engender a dangerous mix.

A fork mounted windshield - by its very nature - is a huge unstable/flexible windblock prone to oscillation under high pressure. Given enough pressure (like that experienced at very high speed) it can make the rest of the bike try to follow its buffeting. Large diameter forks/braces/etc mitigate this, but it is still there. I wonder if you would have experienced your high speed wobble if the windshield was not on at the time.

The other items already mentioned in this thread can certainly be contributing factors, but the extreme force of a vibrating windshield that is sending its oscillations into the front forks should certainly be given some consideration as a possible final trigger that sets off the wobble.

I know; because it happened to me one time long ago and nearly killed me. It was on another brand of cycle and when we tried to duplicate the wobble that nearly killed me, could not do it at the same speed that it happened: but once we reinstalled the fork-mounted windshield I could feel the impending loss of stability at a speed about 10 mph less than when it hit me for real (for understandable reasons I chose to decide to not try to recreate the incident and backed off).

IMO if you keep the windshield you may need a lot bigger set of braces and/or fork tubes and/or bushings. Cafe racers don't have Harley-sized detachable windshields for a reason, and anyone who has ridden behind both a fork-mounted windshield and a frame-mounted fairing can testify to the great difference in the stability of the two different designs.

I may be offbase in my thoughts addressing your problem, but evenso hope it may be helpful throw it out there in an attempt to help you find a solution.

[ruger44]

[quote=GJarrett;1611772]

A fork mounted windshield - by its very nature - is a huge unstable/flexible windblock prone to oscillation under high pressure. Given enough pressure (like that experienced at very high speed) it can make the rest of the bike try to follow its buffeting. Large diameter forks/braces/etc mitigate this, but it is still there. I wonder if you would have experienced your high speed wobble if the windshield was not on at the time.



Looking directly at the bike I noticed just how large of a surface area the wild shield has.
I Now feel what primarily triggered both wobbles was the windshield.


Thanks You guys know your stuff.
Ride Safe