Thanks! Not a problem!
I wondered about the road quality. What I’ve noticed is that urban bikes available here in the US have models with and without suspension forks. Anyway, I guess the idea is to have all bases covered.
Back in the 70’s when I got into riding, I bought a book on bicycle maintenance as I had no experience with derailleurs and how to adjust them properly. While I understood how they worked, I had no sense of what made a good adjustment. I didn’t ride through the 80’s and 90’s and started again in the early 2000’s. I bought another book at that time as things had changed in 20+ years. Although I haven’t done much work on my bikes in more recent times, it is good to have background. It helps to describe things better to service people and to understand what they do/did.
This is a cutaway of a geared hub:
There are lots of moving parts that all must function correctly in order for it to shift as it should.
Disc brakes are quite popular these days. The advantages for bikes are essentially the same as it is for cars. They flush water away and dissipate heat quickly. Replacing rotors on bikes is also probably cheaper than replacing quality wheels. I haven’t ridden a bike with disc brakes, but I assume their stopping power is at least comparable to rim brakes.
Flexible belts have some clear advantages over chains. They are quiet, they do not rust and they don’t need any lubrication. They are a good match for geared hubs. However, they require that the chair stay and the seat stay on the drive side is separable. In the photo the 2 hex socket screws are removed and the chain stay separated from the seat stay in order to install or remove the belt.