Trail Calculator

This trail calculator is a bit unusal in that it works for telescopic forks, springer forks, girder forks, and leading link forks. It also only requires you to input three pieces of information. What it has in common with every other trail calculator is that it is only as good as the measurements you put into it.

First off, you need a plumb line, an angle finder and a tape. Use the angle finder to check the ground is level as the rake has to be measured relative to the ground and not the horizontal. If the ground isn't dead level it will throw the last two measurements off, two degrees isn't going to make a huge difference to the height and offset, but you might as well correct the rake reading. A level spot would be better though.

Next measure the rake of the headstock, as long as you aren't running raked cups this wil be the rake of the stem. If you have raked cups add the number of degress they are raked to get the rake of the stem ("R" in the diagram).Raked trees won't affect the calculation.

Use the plumb bob to mark the point on the ground that is directly underneath the CENTER of the stem. Then measure the vertical height to the center of the stem with the tape ("H" in the diagram).

Again using the plumb bob, mark the point on the ground that is directly under the center of the axle. Then measure the seperation between the point directly under the stem and the point directly under the axle ("O" in the diagram).

Enter the numbers into the table below and click on the Calculate Trail button

Dimensions can be in inches (1.5" not 1 1/2" please) or mm and the answer will be in the same units. The angle has to be in degrees.