Aerodynamic Wheel Disks - For your Bike

Step 2 Take Measurements - Mark Them

First, take some measurement. We need to know the radius of the wheel in question (in our case, 7 and 3/8 inches). We also need a hole to allow the quick release nut to go in place -- in case of emergency and we need to pop the wheel off quickly. That measurement was done with a caliper (3/4").

Marking your measurements is quite easy -- mark off the center of your circle by measuring your radius (plus an inch or so for safety) off of two sides of your plastic, then make a cross hair as shown.

Now, use a bit of string and your marker to generate a circle at the necessary radius. Just plant one end of the circle at the center of the cross hair and hold your marker at a radius' distance on the string. Then mark.