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The crown race is a circular piece that sits on the bottom of the steering tube (the single tube attached to the fork) where the tube and fork meet. It forms the base of the headset (the component that allows the handlebars to rotate on the fork). Note that some bikes already have the race built in.  Hold the fork upright so that the bottom of the forks are facing the ground. It's a common mistake to damage forks during installation, so if you place the forks on the ground, rest them in old shoes or on a mat to protect them. Place the crown race over the steering tube and set it firmly at the base of the steering tube.  Crown race installation method A: Since you don't want to damage the crown race during installation, there are two ways you can put it on without damaging it. The first is to place an old headset cup (the cup-shaped component that makes up part of the headset) over the crown race. Hammer evenly around the headset cup to secure the crown race beneath in place without damaging it.   Crown race installation method B: Slide a PVC pipe of the proper diameter over top of the steering tube and rest it on top of the crown race. Make sure the pipe is longer than the steering tube. Now, hammer the top of the pipe until the crown race is secure in place. First, lubricate the top of the crown race by applying a layer of grease. Then, slide a bottom bearing on top of the crown race and apply pressure to set it in place. For integrated headsets, bearings are universal, so you don’t need to worry about which one goes on top or on the bottom. Insert the steering tube into the head tube (the short tube attaching the frame together at the front). Make sure the forks point toward the ground. Slide the top bearing on, making sure that the concave part sits inside the head tube, and apply gentle pressure to set it in place. Slide the cup on top of the bearing. It may be slightly difficult to get on, but it’s supposed to be that way. If you’re using them, slide on the spacers next, followed by the gyro (also called the detangler that allows the handlebars to rotate 360 degrees without tangling the brake cables) and the top gyro plate.  The gyro will slide over the spacers (if you’re using them), the bearing, and the cup, and sit on the head tube where it meets the frame. The gyro top plate will sit on top of the spacers if you’re using them; otherwise, it will sit on top of the headset cup.
Install the crown race onto the fork. Install the bearing. Attach the fork and frame. Install the top headset cup.