Just guessing the steerer tube is actually 1 1/8", and the stem is larger. Pic is of original stem. I'll have to do some research on it. The stem I put on it said it's 1 1/8th . The steerer tube is not carbon, but aluminum .. I did see a video that explained the future shock, saying that the stem is not actually clamping to the forks steerer tube, There's something that bolts to the top of the fork (or something, for lack of better words)