Sunday, September 19, 2010

rSogn Updates

Here is an updated geometry with the addition of size Small. This size is mostly proportional except for head and seat tube angles at 73 and 72 degrees, respectively. That is the best I can do without further compromising the proportion and ride.

The geometry also shows a slight change in rake from 60mm to 63mm. I decided to tweak the rake after riding a 60mm rake extensively with the Neo Moto, the Quasi Moto, the Hetre, and the Pari Moto over the weekend. This was also to address a minor design dilemma I had with the smaller frame sizes.

The standover height is now based on the Neo Moto 58c.

Click on the geometry to embiggen.

Click on the picture to embiggen.

As far as tubing, I am now leaning toward 8/5/8 for all sizes. There might be a slight variation among certain frame sizes. I will share further details as they become available.



Russ Stringfellow said...

Thanks, thanks, thanks for including the small size in your design. The 54 top tube is perfect and 780 stand over height will be great for riding single track.

I'm curious why you are leaning toward 8/5/8 though...not criticizing but just curious.

Also, you mention adjusting the seat tube and head tube to allow less slope. What will this do to stand over?

Anonymous said...

So make the seat tubes smaller on the ML and L to bring the slope up to 7.5? I like the 6.5 of the ML, and unless it gave significant standover benefits, I think it all looks good barring any adjustments you foresee based on how you think the Pari Motos and the Hetres will look.

I think I like the idea of the 8/5/8.

I like that you are thinking how the Pari Moto and the Hetre will look on the bike, and that you did some real world testing of the rake.


Michael_S said...

I'm kind of curious on the effective seat tube measurement. Is that the distance from the BB center to top of top tube or the distance from BB to a flat line from center of headtube/toptube junction?
Overall Sogn is looking very good to me still.


Russ Stringfellow said...


I think the effective seat tube is, like you stated, the distance from bb center to the flat line from center of top tube.

According to the drawings, the seat tube extension should only be a little taller than the top of the top tube.

I don't think there's a center to top measurement in the chart, but it shouldn't be too far off.

Hope this helps, R

Sean said...

@Russ and Mark: I now think that the current rSogn geometry needs no further tweaking; I will leave it as it is. The 8/5/8 will offer some more flexibility as in planing when we ride the Hetre/Pari Moto. The standard diameter offers adequate strength for off-road excursions short of downhill runs.

alex wetmore said...

I'm glad to see the size small and I like where the geometry has ended up. 63mm rake handles very nicely, and your STA and HTA now match my Gifford.

I don't like the 8/5/8 tubing, I think that it is too thin for this application. I went into more details in a long comment on my blog:

Sean said...

@alex: I too agree that the geometry is even better. I have been under the impression that the rSogn would be not be ridden off-road as often as anticipated. But then again you are right that we should stay with 9/6/9 for reasons you had outlined. For what it is worth, Jan and I are of a very similar stature and weight, so I need to remind myself of this when it comes to deciding what works better for everybody. At any rate, I will want to hear from the others as to tubing before going back to 9/6/9 standard diameter.

Anonymous said...

What stature are we talking? I'm 5'11 and 175. All other performance factors being equal, I do enjoy a lighter bicycle more times than not.

Anyway, I would say at this point I would defer to Alex on the tubing, as most of my knowledge is inferred. And as he points out, it's unlikely most of us could tell the difference if our lives depended on it.


Anonymous said...

I currently ride a cross check, which is 9/6/9 SD tubeset, with an OS downtube. I have been able to get it to flex with some stupid rear loads, but mostly it rides pretty good, and the rSogn will have much fatter tires. Honestly, I would feel more comfortable buying a frame a few ounces heavier with a slightly thicker tubeset for when I'm hauling textbooks or drunkenly crashing down trails or all the other stuff my bikes get used for.

Anonymous said...

I'm a lightweight my self and like the idea of 8/5/8 tubes. Any off road riding I would do with this bike would be relatively mild so I'm not too concerned with durability. A compromise which some expressed on Alex's blog would be to have a 8/5/8 tt and a 9/6/9 dt.

Anonymous said...

"..the rSogn will have much fatter tires.."

Again I would say that having fatter tires is actually more of an argument to go with lighter tubes. But anyway.


billiam said...

Thanks to everyone's input, the rSogn is turning out to be a bike I can't ignore, therefore I'll add my thoughts on tubing specs.
I love the ride of my Kogswell G2, which has a 28.6 x 8/5/8 top tube & 28.6 x 9/6/9 downtube. My top tube has 2 noticeable dents from commuter/rack/pole locking usage. I don't baby my bikes, but I have never before dented a tube on my 70's & 80's UJB's. So for me, the 9/6/9 makes for sense for a trail-capable bike.
Bill in San Diego

bsk said...

@ 160 #'s I'm more likely to buy the frame if it is 8/5/8 than 9/6/9. Of course, I have a mtb for singletrack.

Russ Stringfellow said...

I can see your reasoning for 8/5/8 but I'm still in the 9/6/9 club.

If the rSogn is wearing the braze-ons to carry bags, I will probably use them...I won't use them frequently enough, but I'll use them nonetheless.

I'd prefer if it didn't ride like a slinky when I need a stiff frame the most.

alex wetmore said...

@brothersterno: The Cross Check is not standard diameter. Both the top tube and downtube are oversized. The 9/6/9 tubing on it is much stiffer than what is being discussed for the rSogn. The tubing diameter is much more important the wall thickness when it comes to stiffness.

To be 100% clear, standard diameter means a 28.6mm (1-1/8") downtube and a 25.4mm (1") top tube. Oversized is anything larger, but usually means a 31.8mm (1-1/4") downtube and 28.6mm (1-1/8") top tube. The Cross Check uses that tubing, the LHT has a 31.8mm downtube and top tube.

@sean: I hope that people ride the bike on dirt roads and singletrack. The design screams out for it. Even if most of the miles are ridden on pavement the bicycle should be designed to handle the offroad conditions. If it isn't designed for those conditions then there is no reason to make the Quasi-Moto (let alone the Neo-Moto) fit.

alex (5'11, 190+lbs)

Sean said...

@alex: Agreed. It is likely that the rSogn will have 9/6/9 or a combination of 8/5/8 and 9/6/9, depending on frame size.

Jim G said...


Question: will a 1-inch diameter top tube look odd welded to a 9/8" head tube?!?

Anonymous said...

Again a very interesting conversation. I think part of it hinges on the personal biases we bring to the table, too. I come from more of a road orientation. For me it's about having wider tires to ride the dirt sections one might encounter and decide to explore in comfort. Others envision more of an off-road approach. While I like the concept of going from road to single track, how does it work in fact? Can the Quasi Motos be run on the road without being too annoying? Obviously you'll not be riding the road much with Neos. Will they fit on the same rim as a Pari Moto? Can someone recommend a rim as versatile as the rSogn frame?

I guess if I love the wide tire low trail 650B experience I can always keep the rSogn as a mountain/trail bike, sell the rest of my bikes and get a lightweight (all) road 650B.


P.S. Did a great ride over East Mountain Rd. Sunday. The back side is 2 miles of steep downhill dirt road. I look forward to tackling it with my rSogn...but what tires?

Protorio said...


Rob in Seattle said...

At 6'-2" and 210 lbs with the thought of the rSogn being an off-pavement tourer (with ultralight camping gear) for me--but not downhill mtb, I'd prefer 9/6/9 tubing in the L.

I already have a nice road bike. :)