Enter your head tube angle, your fork offset and your wheel, and it computes the ground trail (the table figure) and the mechanical trail (the one that generates self-centering), the wheel flop, and how much trail changes per degree, per mm of offset or per wheel size. Advanced: dynamic trail under braking and under SAG. Closed-form model, validated against an independent numerical oracle. Nothing leaves your browser.
The ground trail is the figure printed in geometry charts: the distance, on the ground, between where the steering axis points and where the tire touches. The mechanical trail is the perpendicular distance to the steering axis, and it's the one that actually generates the self-centering torque. More trail = more stable, planted steering; less = quicker and more agile. To understand what you feel with each number, see the trail entry and the geometry cluster.
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