Street fox - tadpole death wobble.

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I've built two of these and one of them has a serious steering wobble. What could be the cause
 

Radical Brad

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Usually one of two things; misaligned front wheels (toe in or toe out), or worn / loose connecting hardware.

If you remove the connecting rod and roll the trike forward, it will show you the optimal alignment setting because the wheels will drive a perfect track.
Compare this to your actual adjustment.

Brad
 
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Steering geometry is wrong somewhere probably.
Does the axis of both of the kingpins point to the contact -patch?
Are Both kingpins inclined rearwards at the correct angle for self-centering?
What comparisons have you made?
Where's a picture of the bad one Vs the good one?
 
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All other things being equal, the faster you go, the more reactive the steering becomes (same angle but greater travelling distance at that angle), the more reactive you become, the more ...

After some years of Warrior riding I came across the wobble only recently. I put it down to a combination of the affects of track surface camber, track surface profile, corrugations and the natural tendency to self centre, only to be upset by the previous things. Mind you, I had taken both hands off to do something at the time. It was a gravel surface and speed was not great but was mildly scary for a second or so. Ordinarily, it doesn't happen.
 
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I am with the reporter on this .....

Death wobble is because it gets more and more violent after it starts and affects the direction you are trying to steer in ?
 

Radical Brad

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I used to call it that as well.

Remember my first "street chopper" having the effect. I turned an old 150cc Honda into a chopper by bolting cold water pipes onto the triple tree in place of the original fork tubing and proceeded to blast down the street to my friends house. It wobbled me right to the curb in a hurry.

The things you try when you are 14!
That's what stitches are for, right?

Brad
 

Twinkle

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My shimmy at 13 -14 mph was finally cured when I replaced the tyres - from 2.1 to 1.5" marathon speed I believe the bigger tyres ( eastern burnouts BMX ramp tyres ) were out of balance in manufacture as I tried 3 pairs of these ( I did like them ) I had been using these tyres for the last 4 years . I tried franks rubber washers fix a few years ago and found the washers worked but did not last more than a few weeks , the same as over tightening the head bearings ( also tried slugging the USS bearing mount ) all these improved the problem but the tyres have resolved the problem ( since xmas )

regards emma
 

Radical Brad

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Great vid, thanks for posting.

I must have made friends with old Murphy and his law book because I have never experienced trike shimmy.
I usually do the "free roll" method to align the wheels and then lock the tie rod distance.
Next tadpole or quad I make, I will take it to my 2 mile hill and see what happens at 50+ Mph.

Brad
 
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My shimmy at 13 -14 mph was finally cured when I replaced the tyres - from 2.1 to 1.5" marathon speed I believe the bigger tyres ( eastern burnouts BMX ramp tyres ) were out of balance in manufacture as I tried 3 pairs of these ( I did like them ) I had been using these tyres for the last 4 years . I tried franks rubber washers fix a few years ago and found the washers worked but did not last more than a few weeks , the same as over tightening the head bearings ( also tried slugging the USS bearing mount ) all these improved the problem but the tyres have resolved the problem ( since xmas )

regards emma
Interesting. So it's a dynamic wheel balance issue as well, like with cars. Maybe not necessarily the same thing as truing!
 
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In the videos adding the rubber washers did solve the shimmy, but they do perish so you need spares. I tried thicker, more dense washers, but they had less damping effect. You need the sponginess of the washer to damp the shimmy but that comes at a cost, washer longevity. I think the real the problem comes from, at least in my case, "home garage engineering" and the caster angles not being exactly the same on both sides. Then the tyre pressure and the tyres themselves all add to the problem. But the washers certainly helped.

Cheers
Simon

Glad my videos helped :)
 
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....the washers I used were about the same density as tap washers, ie fairly hard. They were already countersunk as seen in the pic, and this made a better fit over the steering joint 'ball' part. Not sure what these washers were originally intended for, just found them in my odds&sods stuff. You could easily use some large tap washers and punch larger holes in them, experiment and see. Mine have been on my trike a few years now, with no further tinkering needed, and still no shimmy. I'm convinced adding stiction is the way to go......
 
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