The Road Trip has been cancelled.Stability Issues
I was unable to go very far today, thus I returned and disassembled the trailer from the bike. This configuration is not suitable for this much weight â€“ and in fact was not much of an improvement over the Bob Ibex trailer
it was designed to replace.
Generally the symptom was that the axial twisting of the trailer bike frame
propagated forward and radically affected steering as speed picked up, creating instability and inability to control steering. This issue does not manifest going uphill. At the most fundamental level I deemed the arraignment unsafe at any speed under heavy load
. Contributing factors
No single element is responsible; several played a part and worked in concert to generate an unsafe experience.
- Bike Frame: The dual-tube inline framework from steering to rear axle is inherently unable to cope with wide loads. A better design would be one of three tubes arraigned as a triangle in cross-section from front to back, like a 3-pole truss. This would reduce the axial twisting force greatly if designed correctly. Instead I relied upon a single unsupported CroMoly tube passing through the Bottom Bracket. The twisting was most evident when under heavy load, and oscillated when speeds reached beyond 5 mph.
- Wide Hookworm Tires: These wide balloon tires have great traction; however they have a poorly-constructed sidewalls which allows the rim to move laterally from side-to-side during cornering. On a two-wheel bike one hardly notices the effect. Yet on a trailer that is oscillating, the rhythm is enhanced by the wandering of the rim upon the wheel; the very nature of soft suspension Balloon tires profoundly enhances movement by having weak sidewalls. A better solution would be to upgrade to DOT tires.
- Full-Suspension: A full-suspension bike frame generally has one or more pivot points. In my case I have multiple between three links discounting the shock absorber that connect the rear frame to the main frame. The bearings that are used on this frame are suitable for a single human rider, possibly with a knapsack. Generally they do not make bike racks for FS-MtBs because of the wide assortment of articulation, and that the pivots are not designed to handle lateral loads; there is too much potential play in the linkage to create a stable towing foundation; this I learned today. The proper solution would be to use oversized bearings to prevent lateral frame deflection such as found on motorcycles. Earlier I noted that having my secondary battery bag on top of the bike rack created scary conditions similar to tail wagging-the-dog. The trailer loaded up with gear magnifies this effect by just being a large link or lever with huge mass.
Unfortunately all this scientific explanation cannot fix the problems today. If I were to apply a correction then the Because-Simple bike frame would need to be replaced. If money were no object Iâ€™d have a custom trailer made-to-order likely using two wheels for stability and eliminate twisting altogether. This is not going to happen soon.
Therefore I wish to say that the bike trip to California is off due to instability
. I am far happier to have a failure at the beginning
of the trip than if it were later
when in-between desert towns, although clearly I am disappointed for losing the race altogether. Not all is lost though as my eBike is in top-flight shape, and much was gleaned from the trailer exercise.
On the bright side, I can now focus on my next project, and possibly go back to work sooner to create a budget for the next project or two. For now â€“ I am ready for a nap.AFTER NAP:
I got up and discussed the issue with my senior pit crew (aka Uncle); Unc thought that I might need more tongue weight. Intrigued, I hooked the trailer back up and loaded the batteries (though not connected), and added four gallons of frozen water (kept in the freezer for enhanced energy efficiency) to the front of the trailer, as if I replaced the clothes with more than enough weight. A static wobble test ensued: The assembly now had even more profound wobble â€“ and I was able to detect slop in my full-suspension linkage which could be resolved by adding another washer; certainly a work-item and definitely contributing to the ricketiness. However the smoking gun was staring at me in the face and there was no way this frame could work with this much load.Future?
It is possible that the trailer could be put to use for one of my other potential interests as a Kayak Trailer
; typical kayaks weigh about 40-45 lbs. Thatâ€™s about the best use scenario that I could come up with.
For now â€“ Iâ€™m taking a break. Iâ€˜ll write more later - and post the final pictures.
Dreaming of new plans, KF