Even if I lock the tilt in the most upright position, it doesn't stop at 90 degrees. Is it defective? March 29, 2021 02:09 Updated It is supposed to be fixed at an angle slightly greater than 90 degrees even if you lock the tilt in the most upright position.We suggest you adjust the tilting tension to see if it helps. Related articles What is the difference between T50 and T50 Air? I want to fix the backrest at a certain angle. Do you have any suggestions? Is there a warranty on the items you sell? How can I contact SIDIZ? I want to fix the backrest at a certain angle. Do you have any suggestions?