I have a bike with 20inch wheels and Magura HS11 rim brakes. On the rear wheel I have just replaced the rim, because the old one had split after many thousand kilometres. The new rim is an Alex DM24 406X24. The old one was another wide aluminium rim.
The Maguras were braking fine with the old rim. In contrast now with the new rim the brakes do not work well: After some initial moderate stopping power the brakes do not grip harder when I pull the lever harder.
To explain it a bit more in detail: When I press the lever slightly (say, of a “feels-like’ amount of 10%) the brake reacts as expect by braking of “10%”. But when I press hard, say 50% or 100% (=as hard as I can), the breaking power does not increase at all, it stays at around 10%.
I am pretty sure it is not an issue with the brake system (oil, etc), because when pulling the lever I feel that the pressure against the rim increases. (Furthermore, not oil is leaking out and the brake behaviour is consistent over days.)
I guess it must have to do with the brake pads an the rim surface. The rim looks to me like it has normal alloy sides, so I kept using the old black brake pads.
So, what might cause this strange behaviour? Should I replace the pads with pads of another type? Or is there another fix?