Slow speed steering wobble with 2008 Suzuki Trike
With my 08 Suzuki Boulevard Trike I experience a lot of steering wobble, especially at slow speeds over rough surfaces. I had read some info about rake and trail for the front forks - would like to know more. Also I wonder if anyone has ever installed a steering damper on the front assembly. If so where would I get one - I am located in Ontario, Canada. Perhaps Lee - Mann will see this and have some suggestions. (Thinking)
Re: Rake and Trail on trikes...
I have no doubt the measure of importance of this to many riders of trikes. However, with that said, in terms of wobble of the front end at any speed there is one cause of that and one only. Specifically that would be that the plane of the rear axle is not in a directional plane exactly 90 degrees to the front wheel. While there can be little doubt that rake and trail may mitigate the occurrence of this wobble, it is important not to lose sight of the forest for the trees.
Having setup several trikes with and also without HD FXR rubber-mounted type frames, in my experience, no trike minus the isometric properties of the rubber mount frame should exhibit wobble of any significance at the front forks when properly aligned. To give the best possible representation of this, I will use what is available on the keyboard to illustrate. [B]_|_. Here the vertical line represents your front wheel in its straight ahead position and the two horizontal lines represent the plane of your rear axle.[/B] [U][I][B]The only thing that will make that front end wobble is when those two alignments are skewed.[/B][/I][/U] While turning the handlebars does change this relationship somewhat, it still does not induce wobble, it simply steers the vehicle in a relatively expected fashion. When traveling straight ahead the front end should have an equally applied lateral force on the front wheel. [B]If the 90 degree angle of relationship between these two planes is not properly enforced, the wobble is the immediate effect of the whole geometry of your chassis perpetually attempting to right itself as it struggles to deal with two differing lateral forces applied to the front end from one side as opposed to the other by the rear wheels.[/B]
Further I will note that the amount of distance outward to either side of the center point of the front wheel also has no wobble-inducing exertion of force on the front end. Example, ___|_, where the end of each horizontal line would represent the distance of the tire when measured from the plane of the front wheel, even this will not induce excessive front end wobble. Even sidecars must be setup to observe this rule of physics. Furthermore, wobble (when it exists at all) just as "Critical Speed of rotating mass" will be accentuated or more or less prominent at certain RPMs or speed, it still exists solely due to forces of physics which are diametrically opposed and at odds with each other.
The absolute best example of this I can point to for a true real-world example is in a true Positive Traction rear end or actual live axle attached to a 3 wheeler. In such cases, a 3 wheeled vehicle is virtually next to impossible to move setting at complete rest with the front wheel cocked at an angle! Until the front end is used to remove the characteristic opposing force of the 2 rear wheels trying to move forward at differing rates of rotation by righting the whole structure back into a perfect right angle to one another, the structure is fighting itself. This opposing force does not correct itself with speed, it usually only serves to get further pronounced with more speed. Wobble however is not a thing we as trike riders must accept as a reality. More on this further down in this post.
There was at one point in time a significant number of live axle trikes on the road as most trikes (other than the servi-cars) were being built by custom creators at one time. And to be clear, any trike configuration of this nature had to be seriously manhandled and also would have inherent wobble at times in maneuvering, not to mention violent instances of flipping over. Even with the isometric setup there is a nominal amount of wobble due to the fact that the perfect relationship of 90 degrees is not set as a result of the rubber giving way at some points even if for very brief moments. Rake and trail adjustments on a trike will indeed serve to make the vehicle easier to steer under certain conditions, but it should never be the first avenue of correction in stopping wobble.
Given that one has the typical adjustment inherent in chains and sprockets or belts and pulleys, it is very easy to use the immediately discernible forces in opposition here in order to adjust this relationship of the rear end to the front end. This can be done by loosening both sides of the binding force of each side of the axle where they are attached to the rear end. With both sides loose, simply grab the handlebars and turn them even a little bit side to side and observe how the sliders move within whatever means they are normally attached to the vehicle. Even the slightest of movement of the front end will be easily visible in the sliding areas of pivot where one would adjust the chain or belt. Now, armed with this knowledge, move the rear wheel closest to the actual drive-line (chain or belt) very near to the tension you desire your chain or belt to be when properly adjusted. This should be done with the front wheel as straight as possible. Bind that side down tight. With the one side clamped down tight, now go to the handlebars and give them a good left to right tug. Moving the front end even just a little will force the other side to come to rest at the point of least resistance. Allow the front end to come to rest at center or the straight ahead steering position. Hold it there and bind the other side down and then recheck the tension of your belt or chain. If the tension is within specs now roll the bike forward just a few inches and observe the force on the front wheel as you attempt to roll both rear wheels straight ahead at the same rate. If the front end rolls even a few inches before falling to one side or the other violently or rapidly, then you have probably achieved very close to the perfect relationship in terms of true.
Hope this helps someone having the wobble experience with their trikes. Let no one convince you however that wobble is something all trikes do. This just is not so if everything is properly aligned. And again, while it is a factor of very minimal consequence with a rubber-mounted frame, it should absolutely not be a factor with typical chassis alignment outside of this one exception. And in closing, I apologize for what seems like an exceptionally wordy post here, I was simply trying to cover all of the many various scenarios of the equipment and methods utilized by each in order to accomplish the desired objective.