Tuesday, September 14, 2010

rSogn Geometry and Sizes

Here is what we have after some more discussion yesterday. We seem to agree on the following numbers:

  • 73d head tube angle
  • 60mm rake
  • 72d seat tube angle
  • 44cm chainstay
  • 65mm bottom bracket drop 

You will notice that this one has some more slope. I also wanted to add that the head tube appears longer because the axle-to-crown length is about 15mm shorter at 385mm. The 50mm head tube extension has reduced to 15mm as well.

Here is a drawing of the small rSogn as discussed:
Click on the drawing to embiggen. 

Here is what frame sizes and geometry for each respective size would be like. Just so you know I have decided to keep frame size system similar to that of the Drakkar.
Click on the table to embiggen. 

What say you?


alex wetmore said...

I like it, except for the misleading sizing names (SM is like most companies mediums).

Have you made any decisions on tubing?

rory said...

I think this is very cool, except i wisht the large was 1 cm less in the top tube.

will it fit the neo-motos?

franklyn said...

The small is really a medium, and the medium is really more like the M/L 1st-gen Sogn.

alex wetmore said...

One more comment.

The 50mm extended head tube on the original Sogn was a bit ungainly, but I think 25-30mm makes a bit more sense here. Moving the top tube 10mm down the head tube will get you 5mm additional standover.

Can you add one measurement to the chart? That is the effective seat tube, which is where the top tube would intersect the seat tube if the top tube were level.

Rory: It looks like the Neo-Moto fits, he is reporting trail with 58mm tires.

Sean said...

@alex: I understand how the proposed sizes can be misleading. I wonder if they should be listed in the length of either seat tube or effective top tube. Would listing the effective seat tube length of each size help in this regard?

I am awaiting several confirmations from my manufacturer on tubing. I will bring this up again on Thursday when we discuss tire clearance.

I too agree that 23-30mm of extended head tube makes more sense. I can post a drawing with this revision; I wanted to ask everybody if the slope is fine. Or should it be less or more?

@rory: Yes, the rSogn as proposed can take the Neo Moto 2.3, or 58c. We will discuss this further on Thursday.

@franklyn: What do you think of labeling sizes with numbers, not letters?

jimmythefly said...

Looking good! I even like the color (really!). re: sizing I'd prefer it be consistent with the previous Sogn as much as possible when it comes to size names. I like size names (vs. numbers) because it removes the implication that one number is all you need to know to find a bike that fits.

I shop(scrounge used bike shops) by looking at TT length first.

rory said...

i retract my statement about wanting 1" less. after doing the math, yes, the 61 is what i would buy.

Anonymous said...

This is looking very nice. Since you asked, I'm for going toward less tt slope whenever possible for this all surface road machine, especially with its old-style Euro st angle (and, one hopes, standard diameter tubing.)

Not knowing how the rake/trail #s equate to handling experience, can someone tell me what general characteristics might be expected with 38-42s, and then 58s? Will this be a bike that can hop into a club ride? I always fantasize about light touring, day trips, etc., but in reality I'm often on 2-4 hour zippy rides.


Anonymous said...

Ahem, please keep the head tube extension 30mm plus: all will appreciate as you get older/more rickety: just jam your stem down until you (and you will) need it.

Michael_S said...

Everything looks good to me so far. I'd be ok with more headtube extension and a little lower standover but I can live with both. The MD looks perfect for me size wise. Looking forward to braze ons and other frame details.

Anonymous said...

Is the standover based on 58s or 38s? I did not see it mentioned anywhere.
I'm not very familiar with tires in these widths. Maybe it's not much of a factor? If it is significant, and the standover measurements assume 38s, I may be leaning toward Alex's suggestion of bringing the tt down 10mm.


alex wetmore said...

"Ahem, please keep the head tube extension 30mm plus: all will appreciate as you get older/more rickety: just jam your stem down until you (and you will) need it."

The discussion hasn't been about making the head tube shorter (which is what affects handlebar height). It has been about where the top tube intersects the head tube.

If the top tube were level the head tube extension would probably be around 100mm (just a guess). Sean has sloped the top tube ~8 degrees, so now the extension is only 15mm. I was suggesting reducing the top tube slope slightly, so that the extension is increased, but the head tube length is the same.

The handlebar height will be the same either way. A little more head tube extension and a little less top tube slope increases the standover slightly.

Anonymous said...

Oops, I see a mention of standover based on 52 Pacentis. As Roseanne Rosannadanna used to say, "Never Mind."


Anonymous said...

I still like dropping the tt a tad. The Med. is a hair bigger than my 58-59s with 28s or 32s. Might want a smidge more room on a gravel-going bike if it's there for the taking.


frank_a said...

The medium as is looks like a great fit for me. Alex makes a good point regarding the HT ext. but either way shouldn't be a deal breaker. It's coming along quite nicely.
- Frank

James Black said...

I think those numbers look great! Nice job. It's interesting seeing how two quite different ideas emerged and developed with the rSogn and the Snekka.

The largest size is pretty much my ideal geometry. It's nice to see a frameset with such a long effective top tube, as roadish bikes often stop before they get this big for some reason.

James Black

John Speare said...

Ok Sean, here's a longshot...

You know how you said you'd do a smaller small if you had 5 pre-orders? What if... and this is a big what if... you made a small small with 26" wheels?

Is that crazy talk? I'm not talking about a tiny small -- just one with a slightly lower stand over... say mid 70's or so.

My wife could just fit over your current "small" -- but a bit more clearance would be ideal and would be closer to a true small for other not-so-tall riders. And with 26" wheels. Wow. That would rule.

Jim G said...

Question: while I'm a proponent of the low trail design, has anyone spent significant time riding a low trail bike offroad _without_ a front load/handlebar bag? Low trail is great provided there's some cargo weight up front, but without it, not so much. I'm concerned about this for those who might want to build this frame into a dedicated trail bike vs. something more rando-oriented. Ideally, I'd love to see a fork with a dual-position dropout ala the old GT Tachyon (and I'll plug James Blacks' dropout design here), but an alternatve may be to offer multiple forks with different offsets ala Kogswell. Thoughts?

Jim G said...

Also, please -- 132.5mm rear spacing!

Protorio said...

+1 for 132.5 spacing. Also +++ for less slope on the top tube. To be honest, I'm not terribly interested in standover clearance. But whatever you can do to get that tt less dramatic and more traditional, the better in my book. I liked the tt slope from yesterday.

Overall, looks like a fantastic design.

Jim G said...

James' dual-position dropout: