Low Speed Wobble

[fatboy]

I just finished converting my 2001 Fatboy to a Mystery Designs IRS trike. It turned out perfect except for a low speed wobble that doesn't go away. I changed the stock 16x3.5 front wheel to a 18x3.5 RC Compontant wheel and a low profile Avon tire that seems to fit perfectly. Except, now that I think about it, the new wheel is almost 1/2" narrower than the stock and i used the same spacers, not even sure if I have the most chamfered end facing away from the wheel on both sides, or even if that would make much of a defferance. What do you all think or know what could be the problem? I have a 7 degree steering head that makes it easier to steer and eliminate high speed wobble but there has to be something else that i may have overlooked. Any help is greatly apperciated. I'll try to attach a picture or two.

 

[screwball]

WOW, a front wheel wobble be it low speed or high speed would scare the hell out of me. So many places to look!! The front wheel spacers being 1/2 inch too short is a good place to start. You mentioned a 7* steering head, did you have the steering knuckle cut/welded, or is the 7* in the triples? Did you tighten the steering bolt to specs, or was the triple tree aligned before tightening? I know some folks aren't too keen on taking their trikes to mechanics, with a steering wobble that is the first place I'd take mine. At 69 I'm too young to die because I started wobbling at 70mph

Good Luck and enjoy that scoot!!

 

[fatboy]

picture of mystery trike

 

[Gorilla]

picture of mystery trike

Nice

 

[dirtdobber]

I did not notice where you went to the 7 degree triple tree or not. If you haven't that is part of the problem. If you have your neck bearings need to be tightened some.
They ride stiff, ISS, this adds to the jerking or wobble. Go to a 7 degree and tighten the neck bears slightly over spec. The 7 degree comes with one bearing and race. It will make a Hugh difference.
mine

 

[pcombe]

picture of mystery trike

A low speed wobble isn't all that uncommon going over a bump or some such, Maybe it's a matter of getting used to it?

Mine can have a low speed head shake under those conditions and I know everything is right because I did myself. I got used to it and don't require a steering damper, If I thought I did I would do it. My trike never has any wobble when I am in power band.

Keep in mind that a damper is actually making it a bit harder to steer so you would have to get used to that too. Keep in mind your Harley has bookoos of low end torque.

On some trikes I have ridden they seem to have a tendency to wobble if your lugging the engine.

Before you get to excited about things take your trike out and run it always keeping it in a gear where the engine is pulling and see what difference it makes?
Under those conditions they seldom had a head shake.

I will agree however that the steering nut must be tighter than stock.
If your manual says 40 lbs. torque try 60 lbs.?

The bottom bearing in your neck should be a conical type bearing especially if you added a new raked triple tree and a conical bearing can stand a whole lot more abuse than a standard flat bearing.

For pictures and explanation of how I set up my front end Google-pcombe library/ photobucket.

 

[captdanwh]

i agree with the thought of the wobble going away if the engine rpm's are pulling your ride. i had a real small wobble at 40 to 42 mph and only at that speed. if i drop a gear and go the same speed the wobble goes away, do not understand it but it does go away so sometimes things are better left unknown.

 

[FLTR2008TRIKE]

I made this crude drawing I attached to illustrate what I think is the dynamics of the steering wobble.

The trike is a triangle setup. The rear end being wider and always pushing straight. The right side on most setups is the power side that moves the trike forward. As you ride or slow down the torque pulse from the drivetrain through the rear end pushes and lets off, push and lets off. As its doing this the right side of the rear ( power ) is pushing then releasing the push. This I think is causing the wobble you experience at slow speeds or slowing down.

Other factors that I think can increase the wobble effect are

Rear end alignment

Drive belt adjustment

Rear tire pressure

Steering head bearing adjustment

Engine mount bushing wear and rear end bushing wear

Condition of the road surface ( Tire ruts, cross slope of the road for drainage )

I dont think the wobble effect can be eliminated, but can be reduced.

 

[pcombe]

i agree with the thought of the wobble going away if the engine rpm's are pulling your ride. i had a real small wobble at 40 to 42 mph and only at that speed. if i drop a gear and go the same speed the wobble goes away, do not understand it but it does go away so sometimes things are better left unknown.

Come to think of it I started running my front tire at full inflation and it also made a difference.

 

[pcombe]

i agree with the thought of the wobble going away if the engine rpm's are pulling your ride. i had a real small wobble at 40 to 42 mph and only at that speed. if i drop a gear and go the same speed the wobble goes away, do not understand it but it does go away so sometimes things are better left unknown.

I experienced the same problem after I converted my bike.
I inflated the front tire to it's called for max. pressure and it went away. go figure?:Shrug:
After I started running a rear tire (turned backward rotation) on the front
The problem never presented its self. I still run max. press. in front tire.