How to Calculate a Rake & Trail

People who are enthusiastic about racing and other competitive sports sometimes use custom-built bicycles. These can be road bikes or gas-powered dirt bikes. Whether you are racing dirt bikes, riding down paved roads, or even considering a trick bike you need to consider the geometry of your bike when you design it. The rake is the angle between the head tube and the ground. The trail is the distance between the point where the front tire intercepts the ground the front steering axis. Both of these measurements affect the efficiency of your bicycle.

Things You'll Need

  • Bicycle
  • Camera
  • Printer for camera
  • Calculator
  • Protractor
  • Pen or marker
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Instructions

  1. Rake Neck Angle

    • 1

      Take a photograph of your bike standing upright and print it out.

    • 2

      Draw a line down the head steering tube to the ground with the straight edge of the protractor.

    • 3

      Draw a line perpendicular to the ground straight down from the top of the head steering tube.

    • 4

      Measure the angle between these two lines with your protractor. That is the rake or rake neck angle.

    Trail

    • 5

      Measure the radius of your bike's front tire.

    • 6

      Take a photograph of your bike standing upright and print it out.

    • 7

      Draw a line down the head steering tube to the ground using the straight edge of the protractor.

    • 8

      Measure the angle of this line to the ground. Be sure to measure the smaller of the two angles, the one facing the bike rather than away from it.

    • 9

      Draw a line perpendicular to the ground going up to the center of the front tire.

    • 10

      Find the distance between the head tube line and the center of the bike. This is the fork offset.

    • 11

      Calculate the trail by multiplying the radius of the bike by the cosine of the head tube angle. From that number, subtract the fork offset. Divide all of this by the sine of the head tube angle.