Question about tremolos

It is difficult to give an answer. Let's say that speed also has to contend with the required expressive intensity. It also depends on the ability developed in the rotation gesture, which in my opinion is essential to easily perform the tremolo without generating muscle fatigue. In Schubert's Wanderer, in the finale, which you can listen to me playing in the Audio section (My Wanderer), there is a crescendo in strength and expressive intensity that makes the long passage very difficult. Sometimes it is even better to think of it not as a balanced alternation, but by leaning the outer part of the hand, lightening the thumb's support where possible (it depends on the pattern of accentuation). In short, case by case, it must be resolved with taste and without reaching the limit of fatigue, also involving, for example in a crescendo, the participation of the forearm and shoulder muscles, etc.