Joe King1 said:
Purely in the interest of discussion purposes I'll take the opposing view that bearings ARE a better choice in THIS application.
Chambers is not building a 500cc 250 lb. dirtbike to be ridden at speeds in excess of 60 mph....he's building a 60-70lb. ebike that will rarely exceed 30 mph...BIG DIFFERENCE.
I just took apart my rear suspension on my 60 lb - 30 mph ebike with full intention of having to replace all the ball bearings in the swingarm & linkage after 2 years (1600 off-road miles) & determined it wasn't necessary.
Bushings lack the structural integrity to resist torsional loads that steel bearings have. Ball bearings have the obvious advantage of less friction & will maintain their size throughout their useful life.
I will step in for discussion purposes. Thanks Joe and good pionts, you are right about the bearings are a good solution in this application (if proper machined after welding and really good looked after). But lifespan is short and must be changed frequently, on failure they really often jam up and destroy their seats or break their frame-part. Their light friction+non slipstick effect is the main advantage and this gets more interesting as speeds get higher!
But my practical experience repairing and machining lead in PTFE or PA6(printable) bushings on (stainless) steel, as rust seams to be the only problem.... Easyer to make, better dirt resistance, shock absorbing and damping, sightly adjustable by clamping force, non noticeable change on rearends feeling(aka slipstick) even at full speed. Downsides: cooling at machining, hard to calculate the pressfit diameter change for the inside beforhand.
Considering the forces (same torque on this bike as an 500cc at the swingarm pivot) and movement at swingarm pivot... An engineer would(should)go for bushings! ( over 100 pieces the engineer gets told to go bearings, out of cost reasons)
Even rubber bushings all cars still using today are really good for this application. And car ball joints are PTFE-steel bushings as well. My Vertemati 495 has PTFE-coated-steel bushings compaired with Öhlins suspension factory side. These coated bushings are the same than in "every telescopic fork" on the marked
The damage(short lifespan) on bearing comes from to short movement (unevenly wear) of the balls inside which leads to the displacement of lubricant, as well as rust. many small balls and big ball track diameter is necessary, which makes them more expensive then bushings...