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gcartelli 08-20-2020 02:32 PM

Looking for assistance with/for custom geometry
ve recently got a fairly good GURU fit and i need some assistance translating the numbers into a solid geometry. I've tried all the various tools for sizing but I keep running up against the apparent need for 50mm! of spacers in order to preserve drop and reach...unacceptable!

I'm looking mainly for advice on who i could reach out to in order to have a custom geometry drawn up (the manufacturing is going to be Chinese). However if anyone wants to lend a hand, my numbers and specs are below. Thanks!

Edit: Current rough diagram: Here

My specs:
  • 5'8", 136lb

Design specs:
  • Short headtube (110mm max)
  • 0 degree toptube (sloped if stack makes standover height impossible)

  • 711mm saddle height over BB (47mm saddle height as component)
  • 47mm saddle setback from BB
  • 65-85mm drop (70 preferred but other options acceptable to slam that stem, or have 10mm max spacer)
  • 490 +/- 5mm reach

GURU Dimensions (L+R from BB, saddle is measured to rail center)
  • Saddle X: 197mm
  • Saddle Y: 633mm
  • Handlebars X: 439mm
  • Handlebars Y: 604mm

Component specs:

  • King inset 1 headset: 22.2 total stack (8 top, 14.2 bottom)
  • enve 2.0 road fork: 367 Axle to Crown
  • Thompson -17 stem (length variable) 36mm stack
  • Zipp Super Short Reach Bars: 70mm reach
  • Saddle, if necc, Fabric Scoop Race Flat: 282 length, 141 center-tip

robt57 08-20-2020 02:41 PM

" I keep running up against the apparent need for 50mm! of spacers in order to preserve drop and reach..."

Seems like you are a candidate for an extended HT and certainly sloped build reading that alone.

Plus the -17 stem seem to indicate you want that to match a level TT. 5-6^ slope and stem to match that just spit balling....

gcartelli 08-20-2020 03:59 PM

Thanks! I know I need to sacrifice the vision of the short HT. Have gotten a bit closer to a functional version Here

Wookski 02-20-2021 05:11 AM


Originally Posted by gcartelli (Post 2780305)
Thanks! I know I need to sacrifice the vision of the short HT. Have gotten a bit closer to a functional version Here

That geo looks super confused- @ 5ft8 are you sure you’re only 711mm saddle to bb? The bike is extremely short and upright- do you have flexibility issues? So many compromises going on it’s hard to offer any advice other than throw out the design and start again.

Peter P. 02-20-2021 05:33 AM

I don't see that 50cm top tube as even being possible with a 700c wheel.
The front wheel is going to hit the down tube. Perhaps that's why it's illustrated as a dashed line in the drawings.

A 5'8" person needed a 50cm top tube-something is wrong with your measurements.

I think you're asking for trouble trying to design the frame yourself. If your specs and such are accurate, you're out of the range of normal. Choose an experienced framebuilder to design around your limitations.

Wookski 02-20-2021 01:44 PM

Here’s an example of a friend’s custom geo from Baum. He’s significantly shorter than you and over 50 years old. Note the slack headtube angle, rake, bb drop and long chainstays: all in all a very stable setup.

gcartelli 02-20-2021 02:10 PM

Thanks for reviving the thread all : ) I moved forward with this a while ago, and its been a pretty great fit all around (Though of course I didn't end up going with the last geo i posted here). It was slightly twitchy at the front, but have swapped out stems as I've dialed in the fit and that seems to have fixed that problem. Currently pondering wether to move to a slight setback seatpost as in retrospect, a slightly slacker STA may have been called for. For the most part things seem to be working out well as is and a setback post will fix that issue if it rears its head.

The numbers came from a Guru Fit, which i slightly tweaked afterwards to account for a larger drop. I am 5'8", with a short torso and long legs, and prefer a compact cockpit (my seat has definitely been bumped up and back a bit from where it was showing previously).

All in all, I'm pleased with the results. It didn't cost much, had been something I wanted to do for a few years and finally had had the time, and resulted in a bike I love to ride that fits pretty well! Thanks for the comments on the fit, however I don't necessarily think that one is always better off having X do Y. Overall it was an incredibly informative process for me to go through and I learned a lot more about bikes, material science, and physics than I ever thought I would, and a renewed appreciation for builders and manufacturers.

Close to production geo on bikegeogalc

And production here:

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