OFFER - linkage (girder, Earle's, Hossack etc) front design analysis

[sebwiers]

I'm doing a Hossack conversion build, and picked up Tony Foale's 'Software for the analysis of alternative front suspension'.

While I'd suggest anybody considering building a custom linkage front end (fork or forkless) get it themselves (at $50, it's a minor cost for such a project), I figured I'd toss out an offer to run numbers for people. Maybe you've got an existing girder fork and you'd like to know what the dynamics are, whatever. Its worth it to me because its kinda fun software to use, and because I'd like to build up a library of (real world) stock designs to gain knowledge from / base new designs on.

I'll post some pictures of what the software kicks out so there's an idea of what potential it offers.

EDIT - Perhaps this should be in the "Suspension" and not "Help" section?

 

[sebwiers]

Here's a screenshot of the configuration for my Hossack build.

Y1 ans Y2 are the heights (above ground) of rear pivot. X = 0 is based on the location of the lower pivot, so X is only specified for the upper linkage. L upritght 0 is the distance along the upright between pivots, L upright 2 is the total upright length. Some of the bike specs (re COG and Wheel MoI) are estimates, but they don't have a huge impact on behavior (only affecting anti dive) and my build is adjustable (via threaded linkage lengths etc) to compensate; once constructed and assembled I can take actual measurements and fine tune.

Design goals were to have zero wheel offset (minimal moment and wind effect) and move the front wheel back compared to stock (possible due to vertical wheel travel) with nearly flat dive / rake / trail figures (or, if not flat, increasing with compression), which graphs show this configuration achieved. 100% anti dive would mean braking has zero dive effect; this may vary depending on the actual COG and how I adjust certain linkages, but the (as judged from trying various changes to those values) the shape of the curve will be fairly consistent.

 

[Tim]

This is pretty cool! I know a few folks have made their own front ends, but I haven't seen anyone with this software. I can move it into the Suspension section - probably the right place for it.