Speed reading is the art of silencing subvocalization. Most readers have an average reading speed of 200 wpm, which is about as fast as they can read a passage out loud. This is no coincidence. It is their inner voice that paces through the text that keeps them from achieving higher reading speeds. They can only read as fast as they can speak because that's the way they were taught to read, through reading systems like Hooked on Phonics.
However, it is entirely possible to read at a much greater speed, with much better reading comprehension, through silencing this inner voice. The solution is simple - absorb reading material faster than that inner voice can keep up.