There are rear hub complete bikes now selling for under $500, and more powerful ones for around $1500, so there is no point in a kid buying a conversion kit and battery, they just ask for the whole bike as a present.
The torque arm will be secured perfectly when first installed. Then someone gets a flat tire in the rain and makes a rushed roadside repair …
Besides, you’re a knowledgeable and skilled mechanic, and serious enough rider to be attuned to when something about the bike is “off”. You’re also young enough to shrug off broken bones.
But you make lots of fair points.
And come to think of it, I’m totally uninformed about what torque direct drive hub motors generate (because I’ve no interest in them, only geared hubs). Isn’t there data on the grin technologies torque arm page? I remember reading it at one time.
It comes down to this .., Torque arms are supposed to be a secondary line of defence. A situation where dropouts provide effectively no defence and the arms are the sole protection is risky.
Is it “unacceptable” risk? No, everybody has different tolerance to risk. But there’s so many safer options that it is most definitely “unnecessary” risk.
Yes, there is data for ta's and its in one of Grintechs presentation videos that he uses power point slides on a screen, he talks about the n.m. before failure of even the most basic of ta's the slotted washer, no ta and their ta's.
I have had hub motors axles spin, rewiring the phase/sense wires is not fun. The only thing that saved me to be able to ride home was I had an adj crescent wrench to use as a ta, with 3m electrical tape around the chain stay. With only one ta I felt the bike wanting to go in one direction more then the other when taking off from a start.