Monday, September 13, 2010

rSogn

As a continuation of the discussion on geometry, I wanted to propose a completely different geometry and then present some more possibilities for discussion.

Based upon The One that started Rawland, this set is markedly different than the geometry as first proposed last week, and could be considered as the basis for the Olaf and the Sogn. It is for that reason I thought it would be worthwhile for us to compare both geometries and then go from there.

Second Geometry

•    Effective top tube length: 56 cm
•    Seat tube angle: 72
•    Head tube angle: 71.5
•    Rake: 54 mm
•    Axle-to-crown length: 385 mm
•    Trail: 59 mm; 54 mm on a 584 x 38 Pari Moto
•    Headtube length: 161 mm
•    Chainstay length: 45.5 cm
•    Bottom bracket drop: 70 mm
•    Standover height: 80 cm, based on a 584 x 52 Pacenti Quasi Moto

Here is a drawing with the second geometry:
Click on the drawings to embiggen.



For comparison, here is the rSogn as first proposed:


Possbilities:

•    Should the trail be much lower at 40 mm instead?
•    If so, should the head tube angle and rake be 73 degrees and 65mm, respectively?
•    How long should the chainstay be?
•    Should the head tube extension remain at 25 mm?
•    Should the bottom bracket drop remain at 70 mm? Or would 65 mm suffice?

Sean

18 comments:

alex wetmore said...

I don't like the 71.5 degree head tube angle. The only reason to do that would be to eliminate toe overlap, but on a higher offset fork that is rarely a problem.

I do like the 72 degree seat tube angle, especially if you are going to make the top tubes fairly long.

I'm glad that you are sticking with vertical and cantis.

I hope that you can get some time on a low trail bike. I think that 73 degree HTA and 40-45mm (depending on tire size) trail is about perfect for this style of bike.

44 to 44.5cm chainstays should be long enough, 45.5 is getting up there.

I'd rather run the top tube higher up the head tube (and have more of a sloping top tube) than a super long unsupported head tube.

I think that 65mm drop is fine, 70mm is too low for a bike that will sometimes be ridden on singletrack.

I just got back from riding a Rawlands dSogn M/L about 65 miles on dirt roads and some singletrack. The existing bike is pretty good, I don't think that major tweaks are necessary. Lighter tubing, a lower trail fork, cantis, and a top tube that intersects the head tube higher would really make the bike shine.

I'm curious about what you'd call this proposed size? Earlier it was called Small, now it is not described. I notice that it has the same standover as the original Sogn but at 1.5cm shorter top tube and 3cm shorter head tube.

Sean said...

Alex,

The size is still Small for discussion. I have not decided whether to offer a smaller frame size with an effective top tube of 54cm, for example. Moreover, all this might depend on pre-orders.

Like the sizing system, the shorter head tube is up for discussion.

Sean

alex wetmore said...

Maybe you could mention what size road frame the size small would compare to? Is it meant to be about the size of a 54cm traditional road frame?

I'm curious to see what the 58-60cm equivalent sizing looks like. That would be close to the M/L in the old Sogn.

Quadmod said...

I like the new version better than the first one proposed. Would be interesting to see this with lower trial, but I like the longer chain stay length as proposed in the latest design. I'd personally like to headtube extension as short as possible and the sloping of the top tube kept to a minimum. Regardless, overall I like how it's shaping up.

C said...

Lose the long head tube extension. It looks terrible and is one of the main reasons I didn't buy a Rawlands the first time around. I'd rather have a more sloping top tube than an overly tall extension.

John Speare said...

I like the original dSogn 73/73 and mid-trail design. It's nice quick handling for a fat tired bike.

I'd love to see a true small with the proposed 73/73 mid-trail canti/650b version in OS 747.

"True small" would put about a 52-ish effective seat tube and 54-ish effective top tube.

I also like the idea of eliminating the tall headtube and doing a more sloping top tube.

Sean said...

@Alex: For consistency with sizing for the Olaf and Sogn, I might make the drawing a Medium, not Small. I will decide on this by tomorrow.

@Quadmod and @C: I have already reduced the extension to 25mm, 50% less than that of the Olaf and Sogn at 50mm. There are practical reasons to the latter; however, I am fine with the reduction. I will check into keeping the extension to 15mm and then increasing the slope by several degrees so as to maintain the standover height of approximately 81.5cm for the size Medium (see my response to Alex above).

@John: I would offer the Small again if I receive at least five pre-orders for this size.

Seabiscuit said...

Hey Sean,

I'm for:
mid-trail design (40mm sound great).
Higher bottom bracket (I run fixed, higher bb gives me more clearance)
Ok with a slopier top tube to bring it up to the top of the head tube.

rmb said...

I'd rather see the original geometry, 73/73.

Phil said...

• Should the trail be much lower at 40 mm instead? - Yes
• If so, should the head tube angle and rake be 73 degrees and 65mm, respectively? - Maybe
• How long should the chainstay be? - 44 sounds good
• Should the head tube extension remain at 25 mm? - i'm open
• Should the bottom bracket drop remain at 70 mm? Or would 65 mm suffice? - i like 70

rory said...

• Should the trail be much lower at 40 mm instead?
I think 45-50mm is good
• If so, should the head tube angle and rake be 73 degrees and 65mm, respectively?
depends on how you took my previous comment, but i like 73 head angles
• How long should the chainstay be?
43mm-44mm
• Should the head tube extension remain at 25 mm?
sure
• Should the bottom bracket drop remain at 70 mm? Or would 65 mm suffice?
no, the Bottom Bracket should be 65mm

Anonymous said...

I like the slacker seat tube angle for many reasons, including better compatibility with leather saddles, weight over rear for loose gravel. Much prefer the handling of a steeper head tube angle. I don't think you need chainstays much beyond 44, especially if the bike will be designed for front loads, meaning no concerns about rear pannier clearance. After that it gets a little cadillacky. I don't know how to compare various rakes and trails, so would cast my vote with the majority here.

Mark

P.S. I've said it before but yes to minimal ht ext, 15 is plenty. I doubt kicking up the seat tube a few mm to keep slope the same would be a ball, I mean a deal breaker. TT clearance is way overrated on road bikes, and there will be plenty in any case.

Michael_S said...

I'm another in the low trail camp. 45mm or so with Hetres would be the ideal target, so 73 HA and 55mm rake gets you there. Chainstays at 43-44. I'm fine with the headtube extension as I don't like steeply sloping top tubes. BB drop of 65-70 is just fine. I ride a 75mm drop BB off road with 175 cranks and rarely have an issue. Please,please keep the 72 SA, even with a setback seatpost I can barely get back far enuf. This is a very cool process...a very good Idea Sean.

Mike

mwebb said...

+1 for low trail and short chainstays. 73/73 or 73/72 ht/st would be ideal. I'd also like to add my support for standard diameter frame tubes, I don't know if this is still up for debate but I've agreed with almost everything Alex has written, his Gifford bike is a great example of what I'd like the rSogn to become.

Anonymous said...

Just from a strictly research (ie google, archives, BQ) point of view, it seems that lower trail goes with the 650B/wide tire/front load territory (although I'm not crazy about handlebar bags--can someone tell me if handling is negatively affected by having nothing up front with the higher rake/lower trail fork?) Also, coincidentally, an interesting thread on the iBob list about the relative unimportance of standover height.

Mark

James Black said...

I strongly feel it should have a 73 head angle instead of a 71.5 - that's way too shallow! Such shallow head angles handle badly with a front load such as a handlebar bag, and I think this bike should be appealing to the front-loading market. I also think it should have 60mm of rake.

72 seat angle would be ideal, I think.

I have no strong opinion about the other questions, the proposed numbers all sound acceptable.

James Black

Anonymous said...

Another vote for 73 head angle and 40mm trail.
BB drop of 70 seems too low, I think 65 is just right for 650B.
72 seat angle sounds great, certainly no more than 73.
I don't care about the chainstays as long as it'll still fit Neo-Motos.
I don't like the head tube extension, but it's not a deal breaker.

Ryan

frank_a said...

72 deg seat tube angle and cantis~ I'm in!
-Frank