Defining the Axle to Crown Measurement

[Kyono]

Hello All,

For my first post to the forum, allow me to start with a simple question:

Is the axle to crown measurement taken parallel to the steering axis, or in direct line from the fork crown to the axle, thus making A-C dependent on rake? Forgive me if this is trivial, but I found nothing but conflicting information online.


Thank you in advance.
Brent Kyono from California

[e-RICHIE]

Brent when I do the set-ups here, my fixture is set to mimic the A-C distance I want on a finished fork. That is, with a surrogate axle inserted into the tips of a fork with a certain rake, I lay a stainless rule across the span and measure from the base plate to the axle. Actually, I measure from the lower head tube because I need to know the distance including the headset parts.

[jon_norstog]

I do the fork up on CAD and use a measurement along the steering axis to define axle-to-crown distance. My old HJ Universal jig doesn't really allow for precision measurement of this distance, but I have a giant vernier caliper (Harbor Freight, $15) and can usually get that dimension within a millimeter or two. The HJ IS pretty good at getting rake where you want it and has a marked standoff bar that will give you a pretty decent reading if you know how to use it. RTFM.

Good luck!

jn

[Eric Estlund]

I use the term "fork length" to mean from distance along the steerer axis, and "axle to crown" as the actual axle to crown distance.

[hampco]

Eric’s definition is consistent with BikeCAD so that would be my pick as well.

[Kyono]

Thanks for all of the replies. I appreciate the definitions of fork length vs. A-C presented here- previously, I had not given thought to them being explicitly different measures, due to lots of dimensioning inconsistencies between OEM geometry charts. I'll keep them in mind going forward.

Cheers,
Brent Kyono from California