bicycle frame dimensions



Trail is the distance between the point where the wheel contacts the ground and the point where the steering axis of the front wheel intersects the ground.

A bike with a lot of trail will tend to ride straight and feel very stable, but will not be as responsive as a bike with less trail.

Lean Angle

The lean angle in BikeCAD Pro is the maximum angle a bike can be leaned with the inside crank dropped to the lowest point of its stroke.

The Lean angle feature in BikeCAD Pro is demonstrated here.

Lean angle

Head Tube Bottom

Head Tube Bottom

Head Tube Bottom is the distance from the bottom bracket to the bottom of the head tube. BikeCAD Pro presents this distance in X and Y components.

The Henry James jig requires a couple of other dimensions that are related to Head Tube Bottom. Head Tube Bottom (Henry James) is the dimension shown below. It is just like Head Tube Bottom except it is measured in line with the steerer tube.

Top Tube Length (Effective)

Effective Top Tube Length

The effective top tube length is the horizontal distance from the top tube/head tube junction to the seat tube. This measurement has become significant as more and more bikes are designed with sloping top tubes.

Effective top tube length is one of three options for defining the length of the front triangle. For more on this, see here.


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