Mounting distance is the exact position of pinion relative to the gear wheel along the axis. Getting it right is critical because even a small error — as little as 0.05 mm — directly affects tooth contact pattern, backlash, and load distribution. If the pinion sits too deep or too shallow, the contact pattern shifts to the toe or heel, causing edge loading, increased stress, and premature wear. Incorrect mounting distance also creates noise and vibration, and in severe cases, leads to tooth breakage. Unlike cylindrical gears, spiral bevel gears have curved teeth that require precise positioning to share load properly across the tooth flank. During assembly, we recommend using marking compound to verify the contact pattern, then adjusting axial shims until the pattern is centered on the tooth flank. Proper mounting distance is the single most important factor for quiet operation, long life, and reliable performance of a spiral bevel gear set.