cyclocross frame feedback please

[jdanke]

Hi,

I'm looking for feedback/warnings/things to consider when building a new cross bike. I really appreciate any notes!

Background:
Three years ago I brazed a lugged cross bike under the guidance of a local builder. To me, the main thing was to knock out a bucket list item on building a frame, but I had raced cross in the past and prepared to step back into it with this bike. I did a couple seasons, then covid. I felt these New England courses use more hairpins than in other parts of the US I've raced, or maybe it's a function of time.

Anyway, I raced my bike ("janke") and a 2007 Desalvo and that gave me an opportunity to think about the differences between the two designs. Now I'm planning on building another cross bike building on what I've learned, or think I've learned.

The first goal is to get the steering feel of the Desalvo. The largest impression is that janke felt harder to muscle around the hairpins, and I suspect that's mostly technique, but also b/c it has a 71.5 head angle with a 45-offset fork (trail in 68-land) and the Desalvo (pretty sure) has a 72.5 head angle with a 45-offset fork (trail in 62-land). Desalvo has a 70mm BB drop and I've only had a few pedal strikes.

The second goal is to make sure I get the bars in a good position, by which I mean drop from the saddle and reach, but because of different saddles am referencing off the bottom bracket. Compared to a pro road fit two years ago, the reach (bb to bars) is about 10mm shorter with about 20mm less drop. These were pretty close between janke and Desalvo, but I feel one head tube is too long (160) and the other too short (130 w/30mm of spacers). I've done what I could while managing standover and lug angles. While I'm working on TIG skills, I'm much better at brazing (comparisons are relative).


Checks:
I've checked that the lug angles are within a degree, including at the rear dropout. I'm planning on socket dropouts (canti brakes) that are 68°, a 57.4 x 64.8 x 7° BB shell (30x17 oval stays), the 78° TT to ST and TT to HT lugs, and a 59° HT to DT lug.

I'm assuming straight stays (dimpled) with 12.5 ends, but haven't played around with that area yet.

OS tubing, thinking Spirit for lugs, no rush on this build but availability may influence. Cyclocross time of year I weigh in at 170-ish. I'm big-boned, honest!

What else would anyone recommend I check or think about?


Drawings:

full_bike.jpg


frame_only.jpg



Thanks again for any notes or feedback!

[e-RICHIE]

I’d caution against straight chainstays.

[nessism1]

Looks like a fun project. I've got nothing to add from a technical standpoint, but looking forward to learning during your build and would like to encourage you to share. I'm actually thinking about something similar. My racing days are way past but would like to build a lugged gravel frame.

Edit: I don't know why my signature doesn't show up but it contains my name. I'm not sure if that's required for this forum but I've seen comments in other framebuilding threads here. Anyway, my name is Ed Ness.

[jdanke]

Thanks for the note on the chainstays.

I'm giving it a shot, using drawings of pre-bent stays found on framebuilder supply. I think I'm getting the hang of bikecad, but it's still slow going.

[nessism1]

I used bikecad to design my last frame and it was SO much nicer than having to draw by hand! I had a full size drawing made but had to play around with scaling a fair bit before the print was actually 1:1.

[jdanke]

Finally got some time to work through consideration of straight chainstays, and think that they look like the best compromise when using a lugged bottom bracket. The decision might be different were I able to reliably weld or fillet braze the frame.

Background:
Cyclocross. Steel lugged frame. Zona oval chainstays. Cantis. Sram Force 1 cranks, 38T chainring. 5mm clearance radii.

I used the 2021 Columbus catalog and the SRAM road fit catalog for dimensions. Not all the dropout dimensions are available from the Long Shen catalog, and I'm not sure that the bottom bracket shell I'm considering is from them. Showing educated guesses, anchoring to about a 7 degree chainstay angle, 6mm from outside of the shell.

Both the 'cross and road S-bend stays have an 8 degree bend on the dropout end. On the bb end, the 'cross has an 8-degree bend and the road has a 4-degree bend. The single-bend chainstay is bent at 10 degrees.

Nominally, the tire at 36 is larger than a "legal" cross tire, but it was how I could get the software to match the real world (e.g., axle-to-ground).

Impressions/Questions:

The main question, always, is whether I'm missing something that's obvious to one of you. Please chime in.

The straight stays look like the best compromise to me: adequate crank clearance, tire clearance improved with a dimple, close fit to lugs. On paper, looks like a 48T chainring works.

The CX stays are a close second with improved chainring clearance -maybe up to 52T - but may need different/wider cranks. Have to stick with narrower tires. The main thing: those stays look like a really bad fit to a lugged BB. Could I work another 3 degrees?

The "road S" stays really start driving that wider crankset discussion. I'm not sure I get the point of these stays, to be honest. Appearance?

The single bend would be great for an adventure bike if the chainstays were closer at the bottom bracket. I have a fillet-brazed Stowe from 1997-ish that my son is using with a 700x45c tires and still gobs of room. I rode that thing all over the place.

From top to bottom: Straight, cyclocross "S", road "S", single 10-degree bend

ZON114OV425_straight.png

ZON114OV425133CR_cxS.png

ZON114OV425133E_roadS.png

ZON114V10425_single.png

[e-RICHIE]

I’ll keep my reply simple and short. I only use the curved stays on the RSCX frames. Mostly for tire and wonky wheel clearance issues. And have never had a chainring real estate problem.

Here: https://www.flickr.com/photos/986633...57621807933711

[randonneur]

I'm no frame builder, but I think you've got those s-bend chainstays modeled with the bend backwards.

Marco Pringle

[nessism1]

I’ll keep my reply simple and short. I only use the curved stays on the RSCX frames. Mostly for tire and wonky wheel clearance issues. And have never had a chainring real estate problem.

Here: https://www.flickr.com/photos/986633...57621807933711

Are your RSCX stays custom made to your specs? And assuming yes, are they available for sale to amateur builders working on personal projects?

[e-RICHIE]

Are your RSCX stays custom made to your specs? And assuming yes, are they available for sale to amateur builders working on personal projects?

They are sold within the PegoRichie tube sets I offer on my site.
I don’t sell individual tubes or break up complete sets.
https://richardsachs.com/frame-building-kits/

[jdanke]

I'm no frame builder, but I think you've got those s-bend chainstays modeled with the bend backwards.

Marco Pringle

D'oh!

I'll re-do.


Thanks, Marco.

[jdanke]

Okay, so here are the re-modeled S-bend stays. Makes more sense, once I think about shoe clearance. I think I just blindly followed the single-bend setup.


First the CX, then the road. Much better, but still wondering about whether they'd work with a 7-degree chainstay angle on the bb shell. How far off is too much to overcome?

I might need to work on round chainstays, or round-oval-round or something, because I only see a couple of 10-degree options, but I'd also have to check BB drop & seat angle to find something in the right ballpark.


ZON114OV425133CR_cxS.png


ZON114OV425133E_roadS.png

[progetto]

You can also dimple the stays.