Per the last discussion, The reason that rim and tire height are used is so that wheel size is easily changed and identified in the drawing or spreadsheet. You could use 'wheel diameter' in your drawing or calculation and be entirely correct but it leaves out a lot of information and flexibility that are vital in the understanding of the bicycle, the tires. Notice that in my print, I see what wheel and tires have been chosen.Ok, I misunderstood your use of tyre height as height off the ground rather than height over the rim. We're arriving at the same dimension (tyre outer diameter) but I'm measuring it directly as I already have a pair of wheels/tyres of the size I want to run.
All chassis design starts at the tires. The problem we have with bikes is that the tire positions need to be arrived at through rules of thumb, calculations, or testing as they relate to the CoM. The touchpoints of the bike relative to the ground will change that in slight ways and different riders in others. Then there's the use of the bike and how this alters our choices. Thus, things get fuzzy.
They are driving dimensions but is a separate component of the design. Handgrip position are decoupled from the frame via the stem and handlebar. So, you can have the CoM and wheel relationship you are looking for and then place the grips where they are needed. Since I'm looking for (at 5'10") front center distances of approximately 850mm, I'm doing a lot of fancy work to get the grips placed but it doesn't change how the bike will work.I was talking about grip reach/stack, not frame reach/stack - you refer to it as grip position above. Grip and saddle positions seem like fairly immutable driving dimensions but I don't see them in either of your lists. Wondering why they're not considered 'driving' dimensions.
I could start with the grip position if my only goal was to maximize front center with standard handlebars and stems but the design and planning work for this is not what I'm looking for and still (in this era) outside of what most folks building bikes are willing to look at.
Bars, stems, and spacers | Peter Verdone Designs
I'll repost the print I shared so that it is in this thread:
At the end of the day, we are trying to use values that communicate meaningful parameters of the bike that let us know how it will behave and fit. We want to eliminate ghost values like reach, top tube length, or ground trail and use only values that get us to where we want and describe the bike accurately.