Why does the bike stand up at BREMSEN?!

Hello! Yesterday I thought about the physics of a bike for a really long time. But somehow I can’t figure out which forces are responsible for setting up the bike when you go into the iron! Above all it is said that this effect should not adjust with the new external brake discs! Then I ask myself again why?! And why is the effect with the rear brake not so strong ..or not at all present. Somehow it would have to with the gyroscope forces of the R The only explanation would be the torque around the steering axle. But you can’t imagine that this is so extreme … but then the external brakes would have to have this effect even more, since the lever is bigger! Bzw. would have to have the same effect with the rear brake! But these forces would be the only logical forces and the only ones to do this.. d could move the bike to set up! Then also the tire width should play a role! Man … not so easy ..and I was once in the technical branch! lol ..is but long ago! Greeting Martin