Is it possible to "lock in" the top tube/head tube junction and kick the down tube/head tube junction forward a degree or 2 and make up the difference with more fork rake? You'd have more flop. But so long as the trail was a bit lower, say, lower than average (58?) you'd still have a light feeling bike that would want to hold corners with stability.

I should think that flop really isn't that much of a component unless you are going to extremes like building a chopper or putting a very heavy load on the handle bars.

Crunch the numbers for a 70 degree head tube and kick the rake out until the trail gets to the high 50's-low 60's (58, 59, 60, 61, 62?) and see where that gets you. Then shorten the front center, bringing everything closer to you until the hoods are in the right place. What's the toe overlap then? IIRC the RB1 had a 73/70-ish geo and people, so far as I can tell, people really liked how they rode.

I'm just spit ballin' I've misplaced the bikecad program I used to play with. The worst that can happen is a few wasted electrons at this stage of the game to rule in/out some ideas. In looking at your current set up, everything about it says you are trying to replicate the fit of a utility Dutch bike. The high close bars and the angle of the brake levers say a lot. It's going to be hard to get different results than you already have with a horizontal top tube unless you have a 38 inch inseam. You might consider a non-diamond frame design or touring/North Road handlebars and just outright own the upright fit.


You can also cut 30mm of reach by handlebar selection. 65-75mm reach on modern bars is a lot more common these days than the 100-120mm reach found on vintage bikes. Then even a bit more can be found to work with between various shifters. TRP brake hoods are loooong. Gevenalle and SRAM are really short. Shimano is somewhere in between.

Edit: While we're here. Short chain stays suck. Err on the long side. The rear contact patch sort of acts like tail feathers on a dart or an arrow. The bike will track nicely. It's subtle. But it's there. IME long(er) chain stay bikes tend to have really nice manners for no real tangible performance trade-off. Especially if you have a very upright fit, the longer rear center will help with weight distribution; taking a bunch of weight off the rear wheel to share more evenly between the two. How long are the stays on the bike you currently ride? It might be a good idea to think about shooting for a similar or maybe even a bit longer. 18+ inches? 20? More?

559x57 is similar in diameter to 700x23 both approx 2120-25 circumference (~340mm-ish radius) For brevity it's not worth hashing out 700x25, 28, versus 559x60, 65 whatever. You get the idea... Point being: Longer chain stays in general will help with tire clearances. Boost spacing of 73 or 83mm bottom brackets and 148mm axle widths and 55-58mm chain lines will also help with wide 60+ 26 inch tire widths. All that boost broohaha may well be beyond the scope of this project. But if you intended to have the 26, 700 "freedom option" in the future it could make sense to consider it from the beginning. 60+ tire widths are hard to stuff in a frame otherwise.

You really should have a strong idea of what components you are going to use before you commit to a frame design.