Originally Posted by
Andrew R Stewart
Clifford- Have you ridden a heavily loaded cargo bike? They are already a handful at times with the load "wagging the dog" to a degree. Add the hinges that pivots are and the leverage changes from what a "standard" suspension is designed to work with one might end up with a loosy, inch worming ride. besides if the load is still directly attached to the suspended wheel the shock to the load isn't much different then a hardtail with load.
For damping shock to the load it is the load that needs to be suspended. I don't off hand know of any cargo bike where the load is the suspended element. Andy
Yes, I have ridden one with 100+ pounds on the rack, but I didn't like the feeling of a high load, and for other reasons, I much prefer the load on a trailer. Most trailers don't have suspension, but I have seen a couple with suspension including pet trailers.
I did end up with a flex problem with my home built cargo bike, perhaps due to a weak front frame, and an alignment issue, then when pushed by a heavy trailer downhill, it can cause handling to be a bit difficult. I haven't had a heavy load on the rack for some time, but I don't think the flex was as big of an issue with the bike alone.
Putting suspension under the rider, and the load unsuspended over the tire might not handle too bad, if one got the spring right. Or, like you say, it could give an odd springing sensation. However, reading back, that wouldn't provide the benefit the OP wanted, protecting the load.
Looking at the photo of the Yuba:
I'm not quite sure where I'd cut it. It appears to be designed with an integral strong mixte style rear triangle.
One could cut at the bottom bracket and behind the seat post, and build a setup similar to the Free Radical on a suspended MTB, but it would do nothing for the load, and give the potential issues Andrew mentioned.
I do think suspension could be built, but would probably require some major reconstruction to work effectively. I.E. building a new bike or rear-end.
I'd probably elongate a frame similar to the Yuba frame, and build a yoke type suspension. Two generally rigid pivots, and a single spring element.
SuspendedCargo.jpg
If one put in two springs for independent suspension, one would risk side by side wobble., and perhaps also damaging one's hub axle and quick release. The rear end would have to be as rigid as possible, thus a pivot and single suspension element.
Pivot could be forward or rearward, depending on how one wished to do it.
An alternative might be similar to vintage stingray bikes where the frame was rigid, but the load (seat) was suspended.
However, care would have to be used to prevent inducing a wobble.
Of course, the simplest option might be just adding more padding to the rack, so the load would be bouncing on foam rather than on a hard surface.
Tire pressure? Perhaps trying the largest rear tire that would fit, at the lowest pressure that doesn't bottom out.