I think I'm running 8s on my cargo bike. I may have bent the axle slightly, but restraightened it.

I think there is a bit of a divergence. Campy and other companies worked on making strong hardened hollow axles for years.

Many of the bolt on axles seem to be a lot weaker. Are they even chromoly, or some other hardened alloy? Simple carbon steel?

Anyway, while I occasionally hit a harsh unexpected bump, I'm pretty nimble on my road bike, so I'm considering experimenting with 8s.

Cargo, touring, groceries, etc, would all add maybe 20% or 30% to my weight... or 20% more potential force on that axle.