I’m building a “city” bike frame for a very upright riding position, but worried about keeping enough weight on the front wheel. My target is 35% minimum weight on front wheel.
Does anyone have any experience with extended chainstays, used to shift weight onto the front wheel, in response to a very upright seating position?
Is 455mm chainstay length too small or too big to optimize weight distribution?
What is considered long will change with the bike’s wheelbase (which depends on rider height and bike purpose, among other things).
Rear center to front center ratio (search RFR on here) has proven to be a useful metric for me when evaluating weight distribution. RFR in the 1.5-1.7 ish range could be a ‘long chainstay’ design IMHO…, which sounds well suited to your design goal.
good thread on the topic:Chainstay Length Discussion - #10 by Daniel_Y
Thanks. I was trying to keep it short but omitted info you needed…
I am 180cm/85kg and always ride a size Large or 55/56cm frame. Configured with a 455mm chainstay, the wheelbase is 1083mm and the reach is 422mm. This will be a “city bike” only ever ridden on clean pavement, so I am targeting an absolute minimum of 35% weight on front wheel while seated very upright.
I wish there was a formula that incorporates angle of rider torso 
I guess what I was implying is that a lower RFR number is better for a more upright riding position where your CG is more rearward horizontally. Your current RFR is 1.38, so you’ve definitely got ‘long chainstays’ by that metric, albeit with a short wheelbase.
But, also consider that your CG is both further back and higher in an upright riding position. That’ll make the bike more easy to wheelie, so if you will be climbing steep hills you might want to factor that into your chainstay length considerations.
Perhaps you could use two bathroom scales to determine your horizontal CG on an existing upright bike, and go from there if you want to achieve 35% weight on the front.
You’ve made the right assumption that a long RC will make for a better load balance. 455 ain’t nothing too crazy. I’ve ridden bikes with 850 stays that still handled fine once you adjust.
The kinda bike you’re describing sound very Rivvy. If you check their geo sheets you’ll see a lot of bikes now have 500+ rear ends.
Thanks! I haven’t thought about them in a while… I forgot how classic and cool those bikes are.