Parts mig / new bike fitup

[J-D Bamford]

“When Richard Sachs ordered his custom Nagasawa road frame, he supplied only two measurements: saddle to pedals and saddle tip to handlebars”.  https://richardsachs.com/nagasawas-influence/. 

This Sachs anecdote inspired me to think more about how a new bike can be assembled to achieve a similar fit to the old bike that’s donating most of the build parts (i.e. you’re moving parts from an old frame onto a new frame).

This has probably been discussed here a lot by long timers. I’m a newcomer, so am sharing this in ignorance and of course am happy for any and all corrections, tips, and whatnot.

Old bike when partially disassembled… measure these three things. Although precisionists would frown, I used a flexible plastic roll-up tape measure sold at fabric stores:

• BB shell (upper OD) to saddle rail
  • It’s best to do this after removing the front derailleur, so it’s not blocking a straight-line measurement.
  • If possible, keep the seat and post together to maintain fore/aft seat position and angular alignment as you transition to the new frame. But if this is your one chance in a decade to disassemble and degunk/de-dirt the seatpost clamp... then so be it.
  • Note that I’m ignoring the crank. Since they rotate in hand, it’s hard to take repeatable measurements off a crank tip or pedal/spindle.
• Front of seatpost (front OD, before it bends towards the saddle clamp) to handlebar (rear OD of the handlebar). 
  • Consider marking the seatpost with masking tape at the exact point of measurement.
• Front axle centerline to handlebar (lower OD of the handlebar)

These are enough to help migrate your key fitup parts to a newer bike of similar design/category (e.g. road/drop bar bike to similar, city/backswept bar bike to similar). Of course your new frame likely has geometrical differences (head tube & seat tube angles are obvious candidates) that will alter fit… but this can still be a helpful start…

New bike - Initial alignment steps:

1. Install seatpost/saddle, using the first measurement above. Get it eyeball close, but don’t fret over a millimeter or two variation. If by chance you’re intending to change crank arm length, then you should account for this now (before moving on to stack and reach topics).
2. Install headset and quill stem. Set quill stem height to approximately the third measurement above. This gives you a close approximation of your previous stack, which affects reach. Or if you intend to alter stack on your new bike, adjust this fitup higher or lower to suit your new goal.
3. Check the seatpost-to-handlebar measurement, the second one above, based upon where the stem’s clamp is positioned. This gives you an approximation of your reach, and helps gauge whether your assumed stem extension is likely to suffice or if you might swap to a longer or shorter stem (to achieve your new target reach) before you do any assembly of handlebars, brake levers, cables/housing, and such. Keep in mind any planned changes in brake hood shape. If you’re migrating from trad/short hoods to modern STI-like/longer reach hoods, then you might account for some difference in stem length to offset the change in hood length (how far forward on the hoods your hands rest).

It won’t be precise, but it should get you real close on the first try - or at least minimizes unconsidered variables and quickens actual fitup adjustments once you’re atop the completed bike. Make any necessary tweaks, consult these forums for further insight… and the rest is just final assembly, ride, and smile :-)

[J-D Bamford]

Bonus content… if you’re futzing with BB lengths and crank Q-factor, temporarily install the BB and then both crank arms *aligned in the same direction* so that you can gauge stance and crank arm clearance from the frame. You'll want to at least wrench-snug the BB axle bolts, so you're assured that final tightening won't move them further inward by even a millimeter when fully wrench/torque tight.

If you’re considering going with a narrower BB spindle than what’s in hand, this temporary fitup will show whether you can go narrower without the crank impacting the chainstay, and without any chainring grinding the frame. No doubt you’ll need a few millimeters clearance on both sides, as parts and their assembly need a bit of wiggle room in case they’re not perfectly symmetrical (i.e. if their rotation is slightly out-of-plane) and to also allow a bit of leeway to keep your shoes/heels from clipping the chainstay (a bit harder to anticipate though).

[Patrick Moore]

Great minds think alike (Mr. Bramford’s, but also Mr. Sachs's). I’ve used a more simple but also more personally tailored method for decades based on a preferred center-of-bb-to-top-of-saddle distance, a preferred saddle setback, and a preferred distance from saddle to tip of brake hoods, **always with the same saddle and brake levers in mind** — original Flites and Shimano aero but non-STI levers. This gives me a good starting position to fine tune over the first 100 miles or so. If I install another type of saddle or brake lever it’s relatively easy to adjust as needed.

More significant is Sachs’s and his mentor’s attitude toward their craft. From the cited article:

“I knew I was looking for something more in framebuilding, and I suspected it didn’t involve “stuff;” without explaining the show in two sentences, suffice it to say that I was inspired by the Japanese reverence for quality handmade articles of any and all types, some important, some mundane, but all constructed with respect to craft, skill, and heritage, and, I suspect, with little or no regard paid to commerce or promotion. My attitude towards framebuilding embraces this attitude. No bicycle could have ever had the impact on my decisions and choices the way the topic of that program did.”

Reading through different articles and interviews on his website, richardsachs.com, it’s clear that Sachs is the closest thing we have in the US to someone like Mr. Nagasawa.

This is really a norm, as opposed to a common practice. It’s all in Aristotle. ("What do they teach them in these schools?”) The end of the artist as such, imitating nature in her mode of operation, is the perfection of the artifact.

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

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When thou didst not, savage, know thine own meaning,

But wouldst gabble like a thing most brutish,

I endowed thy purposes with words that made them known.

[Peter Adler]

Not necessarily the sort of thread where I would normally contribute, but I think much of this artist/craftsman mindset is captured in two songs from Sondheim's Sunday In The Park With George, "Finishing The Hat" and "Putting It Together":

https://www.youtube.com/watch?v=ducG55pfCMQ

"look, I made a hat - where there never was a hat!"

https://www.youtube.com/watch?v=rJFz-ucuTvs
"a vision's just a vision, if it's only in your head"

"so that your work...can go on exhibition"

Peter "art isn't easy" Adler

Berkeley, California