try standing in front of the bike with the front wheel elevated, grab the lower fork tubes and pull back and forth to see if there is play, since this bike is made from parts the steering stem and steering stem bolt or the bolt and bearings might not jive , zooming in on that area in the pic it looks a little odd. good luck
Hey Y'all,
I don't know enough about the geometry and physics involved to be able to explain my hunch....but I think Dave hit the nail on the head.
It is my opinion that mini bikes were initially either engineered correctly through design...or trial and error...that they had a working relatively stable product with the stock front end, and wheels and tires that came stock on the various models offerred.
Once you change any one of those variables, in my opinion, all bets are off, as to whether the ride will stay stable.
That said, I think with some experimentation and switching some of the variables around, you may be able to acheive the ride you are looking for ?
Be sure to wear your helmet while testing things out !
I don't know enough about the geometry and physics involved to be able to explain my hunch....but I think Dave hit the nail on the head.
It is my opinion that mini bikes were initially either engineered correctly through design...or trial and error...that they had a working relatively stable product with the stock front end, and wheels and tires that came stock on the various models offerred.
Once you change any one of those variables, in my opinion, all bets are off, as to whether the ride will stay stable.
That said, I think with some experimentation and switching some of the variables around, you may be able to acheive the ride you are looking for ?
Be sure to wear your helmet while testing things out !
An Excessive bead edge will cause this OR even dry spot mounting ( soap on one side an not the other )
Try this; Deflate the tire, Soap rim and bead really well . Inflate tire while it is suspended, Over inflate by 10lbs or so. Then deflate to proper pressure.
If it still wobbles, I would take tire off and check for Excessive bead edge.
I wouldn't consider 20 MPH on six inch wheels is a low speed wobble. But I was referring to the mud in what little is left of the treads causing an imbalance, along with the fact that there is no tread/traction on the road. When you installed the front end, where you didn't establish rake angle so you could get trail. Does it have trail? Can you flip the lower legs 180 degrees, then remount? If so, that would quickly answer that question as you got the axle more aft.
I tried to edit your photo with lines and words, but maybe you can see enough to see what I mean about trail. Think of a shopping cart, and how it needs to run with the mass pulling the front end. Two wheeled machines need this same concept. Mass pulling from in front of the axle, not pushing from behind it.
I tried to edit your photo with lines and words, but maybe you can see enough to see what I mean about trail. Think of a shopping cart, and how it needs to run with the mass pulling the front end. Two wheeled machines need this same concept. Mass pulling from in front of the axle, not pushing from behind it.
I doubt there was ever a standard for mini bikes, since there were so many configurations. Motorcycles are generally set up with a 30 degree rake at the neck and 2 to 4 inches of trail. If I were looking at your situation, I'd want to see any positive trail, as long as it isn't zero.
Please don't forget what Tom said above about engine vibration. Those Predators are known for it, and since you're having issues on acceleration where vibration is highest, this is a consideration.
I suspect this vibration is effecting something else in the front end. (Maybe that trail being inadequate) or tire and wheel balance. But all of these bikes are build out of balance. The obvious answer to me, given the fact that you changed the front end, is trail.
Please don't forget what Tom said above about engine vibration. Those Predators are known for it, and since you're having issues on acceleration where vibration is highest, this is a consideration.
I suspect this vibration is effecting something else in the front end. (Maybe that trail being inadequate) or tire and wheel balance. But all of these bikes are build out of balance. The obvious answer to me, given the fact that you changed the front end, is trail.
take off the front wheel turn the fork legs 180 degrees and you will have increased trail. Your rake looks like it may be too straight and with the bike sitting nose down it reduces it more. Your axle mounts are forward of the fork reducing trail by reversing it it will increase trail and if that is your problem it should reduce the shaking or eliminate it. Does the front fork compress a lot when you sit on it?
I think it was a combination of several problems. I flipped the legs around like you suggested and it helped the speed wobbles alot.:thumbsup: I also welded some gussets on the bottom of the motor plate to stop some of the vibration and that helped a bunch as well. Next Im gonna get those tires turned around. Thanks for the help!
Outstanding. Thanks for reporting back. I did some looking at two old vintage mini bike frames I have. They ran the steering neck at around 60 degrees, and the triple trees at right angles to them. Simple construction, but as long as these planes are perpendicular, you will have trail, and it's around 1.5 to 2 inches on the vintage small frame minis.