Hello,
I’m new here and could use a few pointers if anyone could help. Essentially I’m trying to make a bicycle frame using grasshopper. Ideally, it would be a soft tail but a hardtail will do for now. I’m attempting to remake this definition from an old post. https://www.grasshopper3d.com/profiles/blogs/parametric-bicycle-frame. I must be missing something because my angles are off somewhere.
Thanks!
Bike Def.gh (23.0 KB)
Units? Angles are in radians by default. On anything with angle input, right click the input and select degrees, a little icon will show on the component.
Think about relationships. I am not 100% sure what would be the drivers in a bike frame. one relationship might be axle to axle. what other features of a bike frame might be dependent upon that axle to axle distance? Or maybe the bottom bracket is the “driver” of all other dimensions. Think about how one dimension or component effects other components. What are your givens? Like wheel size drives the height dimension of your axles. If you know the height of your axles, based on wheel size, maybe you can infer the height of your bottom axle. Wheel size along with axle to axle distance will give you some limits on the left to right (front to back might be another way to label this direction) placement of your bottom bracket etc. So think about your givens, think about the relationships between features, think about limits based on those relationships. Set number sliders and ranges based on those limits. Label everything. Build a definition, noodle it, learn, throw it away do it again…Brute force learning 
Bill
I can shed some light on this since I design bikes for a living. There’s a list of driving dimensions that control fit and geometry and there are some driven dimensions that are important for toe-overlap, pedal clearance, FD angle, trail and such. There are two main approaches. One where effective toptube length and headtube length are used as driving dimensions and one where stack and reach are used as driving dimensions. Both work pretty much the same. Here’s a list of driving dimensions using the TT/HT length
-Effective toptube
-Headtube
-Seattube
-BB Drop
-Rear center (chainstay)
-Seat Angle
-Head Angle
-Fork Length
-Fork Offset
Wheel diameter has an influence on fit and handling but for all intends and purposes is a driven dimension. I don’t use Grasshopper for this but rather SolidWorks design tables, but the end result should be the same since you are controlling the same parameters.
