Thursday, September 16, 2010

Tire Clearance and Tubing

With the geometry and sizes pretty much all set, it should be obvious by now that the rSogn would feature the same Pacenti MTB crown. This one has enough width for the Neo Moto 2.3, or 58c. The axle-to-crown length is set at 385mm.

The rear clearance would be set for the same tire, and will feature s-bend chainstays like those of the Drakkar. With this bend, one can set up the rSogn with contemporary road double cranks with outboard bearings, square-taper cranks with cartridge bottom brackets, and triple cranks.

Like the cSogn and dSogn, the rear spacing would be set at 132.5mm.

While we are at this, the rSogn with its capacity to take the Neo Moto 2.3 will have standard-diameter 9/6/9 tubing for all frame sizes. The head tube would be set for the now-ubiquitous 1 1/8" threadless steerer.

Comments?

Sean

33 comments:

Anonymous said...

Wondering what the thinking is behind OS tubing on the Snekka and std on the rSogn? I only know enough to be dangerous in discussions of tubing so don't worry about offending me with a penetrating glimpse of the obvious here, if there is one.

thanks, DS

Jim G said...
This comment has been removed by the author.
Sean said...

@JimG: What is the diameter of the down tube on your Kogswell? Is it a 28.6 or a 31.8? I suspect it is the former. Let me know and then I will reply to your comment and DS'.

Jim G said...

My 59cm low-trail bike uses 28.6mm diameter tubes, 8/5/8 top tube and 9/6/9 down tube. It has an ongoing problem with shimmy. I'd recommend 9/6/9 tubing on both tubes for the rSogn, at least in the larger sizes, and especially if it's going to be a low-trail design.

Anonymous said...

I don't really know what the tubing parameters are on my bicycles, though two of the three in the fleet that are tig-welded are OS. The third is aluminum. I suspect most of my lugged bicycles, based on heft, are probably 9/6/9 if that's a middleweight steel set, but I honestly don't know. In any case, there are so many variables between them that I doubt I could ever figure out what makes what ride like whatever. Which is a long-winded way of saying: pass.

I do have one question about tire clearance. The Neo Moto is a full-on Mt tire. I've never used one, but what would be the thinking? That you could put this tire on and ride singletrack? Would you want to switch to an off road style drop? It seems a bit aggressive for the kind of rough stuff riding this bike is designed to handle. I'm not complaining, just curious how people envision using this tire. (I understand that the greater clearance also permits fenders with Hetres.)

Mark

Michael_S said...

I don't think you need to go all the way to the Neo Moto clearance to fit a hetre with fenders. Something that fits the Quasi would be enuf. It's not a big deal for me, even though I would prob. never run anything as big as a 2.3 wide tire. I'm fine with the 9/6/9 tubing on the two larger sizes. I would like it stiff enough to run some racks and panniers with 20-30 lbs. Nothing world-tour built but able to handle larger people and/or lighter loads.

Mike

XO-1.ORG said...

Shimmy can be caused by all kinds of things, many of them hard to pin down, but I've never heard of "under-size" tubing being blamed for it.

I set my all-time high-speed record, 72.1 mph descending off Mt. Baldy with a massive, gusting tailwind on an Alan Carbonio, one of the whippiest, and lightest, bikes ever made. No shimmy then, or ever on any of my 14 other bikes. (Actually, the one and only time I had shimmy was when running a Berthoud h'bar bag on a Berthoud front rack on a British bike with a lot of trail and a long stem.)

I know of many who have fixed their shimmy just by reinstalling their headset, or installing a new headset, or just learning how to ride in way which doesn't cause the shimmy in the first place. Over-sized tubing didn't exist for the vast majority of cycling history, most of which took place on far worse roads, or even far worse trails than we have today, so we don't need it now.

Sean said...

Morning everybody. I finally had a chance to review all comments. I wanted to reiterate my intention to use standard-diameter tubing for the rSogn. I also think that it would be prudent to stay with 9/6/9 for all frame sizes. To this end, we need to decide if the rSogn should use the Pacenti MTB crown so as to run the Neo Moto 58c. If not, we would need to look at other options on Monday. Personally, I want to keep the crown.

Hal said...

Jan Heine has a discussion of tubing and shimmy as part of his review of a MAP 650B in the current issue of Bicycle Quarterly. It's worth reading for anyone who hasn't done so already.

rory said...

the crown is awesome, and having 5 mm more of clearence doesnt hurt anything. having too little clearance limits the use of the bike.

Sean said...

@rory: Thanks man. So are you fine with the 385mm axle-to-crown length? This would leave about a centimeter of clearance between the crown and the top of the Neo Moto 58c.

Protorio said...

Let me say something about the 58mm Pacenti tires, as I have many miles on them on my Sogn: they are sublime. I've ridden the same gravel/rutted fire roads on my Pacentis and Jack Browns (so not too aggressive), and the Neo Motos are just an absolute blast. I don't know why the rSogn wouldn't want to have them as an option. Its what makes this bike special, in my opinion. Sure, 58mm Honjos or 60mm Berthouds with fat Hetres will be the de-fact road set-up, but just to be able to run the big 'uns is totally a key design element and a central feature to the Rawland spirit.

mwebb said...

385 axle-to-crown sounds fine, while I may never personally ride such a gigantic 58 tire I know others may want to. However with this fork length what would the clearances for a 42 with fenders look like? Certainly there's room but too much? Would you need spacers to achieve a nice fender line? Not a deal breaker, just curious.

Sean said...

@Protorio: Agreed. That is why I would keep the axle-to-crown length at 385mm. This allows the use of the Neo Moto 2.3, or an effective diameter of approximately 700mm at most.

Sean said...

@mwebb: The clearance with the Hetre 42c, for example, would be about 1.5cm. That should be enough for fenders and some wiggle room. What is your thought on this?

Jim G said...

@Sean -- what was the axle-to-crown measure of the original Sogn fork?

Definitely re-use the Pacenti crown, and keep enough clearance for the fat rubber!

alex wetmore said...

I think that the Quasi-Moto is the ideal dirt road tire for this bike (they are rounder in profile than the Neo-Moto), but building the bike to fit Neo-Motos won't hurt anything. It will give a bit more clearance if someone wants to try and cram in fenders over the Quasi-Moto. Fender clearance for the Hetre will be a piece of cake.

I really like standard 9/6/9 tubing and think that is a smart choice (no surprise there, I've been pushing for it for the last two weeks).

I don't need one of these frames because it is ending up as a mass produced version of my homemade bicycle. I'm going to buy one though for the same reason...I really like how my bike rides and having a second one setup just for dirt will be great.

Sean said...

@ Jim G: The A-C of the original Sogn fork was 399mm. The clearance would be about 15mm less with the rSogn. Is the current length of 385mm fine then? Or should it be 380?

Jim G said...

@XO-1.org (Chris?) -- Have you spent much time riding a low trail bike?

Your response is a little heavy-handed, and seems to imply that I'm ignorant here ("just learning how to ride...").

I know my bike and I know how to ride it so as to prevent shimmy at both low and high speeds -- but it'd be better if it didn't have the problem at all. I've tried two different forks on my frame, one with 67mm offset and another with 58mm offset, and I can definitively say that the increased offset (lower trail) makes the shimmy much worse. And yes, I had the frame alignment checked before I built the bike up. I have not yet tried swapping headsets, though I have tested tight vs. loose headset adjustments (in my case, a looser headset helped somewhat). I've also experimented with different wheels and tires, and varying the front load (from bare rack to a fully-loaded rando bag). More recently, I've installed a low-trail fork onto another frame, which didn't shimmy before but does now.

I have it on good authority that "many of the the old constructeur bikes will shimmy with a loaded handlebar bag". The 650B MAP recently reviewed in BQ shimmied, as did a TOEI reviewed previously. A prototype Boulder Cycle 650B Randonneur built with super-lightweight tubing shimmied, and as a result they opted to build the production models with stiffer tubing. There are many other examples...

Sean said...

@Jim G: I have reasons to believe that the standard diameter 9/6/9 would avert the rSogn from shimmying. I also wanted to ask if there was any discussion on fork tubing of the bicycles you mentioned. I wonder if that may be a factor other than the offset. Fwiw, I do not recall reading anything on fork tubing and construction when it comes to this.

Jim G said...

@Sean:

I'm happy with the use of 9/6/9 std gauge tubing. I think it'll be stiff enough, but not too stiff, plus it'll be more dent-resistant.

Your question about the fork tubing is insightful. Unfortunately I've not heard much about that. Supposedly the top-line constructeur bikes used fork blades with Imperial Oval dimensions -- these were narrower and slightly less oblong than standard blades, for more flex and better shock absorption? Maybe Alex knows more.

jimmythefly said...

Count me in for fitting the Neo-Moto. Huzzah for standard 9-6-9 tubing.

385 a-to-C should be fine I think, but just to be sure someone with neo-motos on a Sogn should do some bouncing and small curb wheelie-drops. I don't think the fork blades flex enough to cause interference at the crown, but it wouldn't hurt to double check.

Jim G said...

Actually can we do 440mm a-c on the fork? So as to make retrofitting a suspension fork possible?

Yeah, I'm kidding! ;)

rory said...

@sean, I think the 385 souds good. if my math is right, 584/2+59(tire dia)+15(assumed knob height)+15(errant rock capture)= about 380, so i think this is about right.

Sean said...

@Jim G: You almost got me! Suspension? Nah.

@rory: Ja. I think we will leave it at 385.

Anonymous said...

I'm down to buy one o' these here rSogns, too. As long as y'all agree with my color choice.

Mark

Michael_S said...

after hearing all this talk about the Neo Moto's I would agree that it should fit on the bike... just in case. I'm glad it seems settled on the AtoC height as well because that was a minor issue on the original Sogn for me. "ie.the gap". This is shaping up to be exactly what I was looking for in a next bike. and while I'm at it.. the Pacenti crown is a thing of beauty and a major drawing point for Rawland, I think.
Mike

franklyn said...

I'd probably run no larger than quasi moto, but fenders with Hetres would be sweet.

My Ebisu has 5/4" diameter downtube, 9/8" diameter seat tube and 1" top tube. It doesn't shimmy loaded up with a Inurijushi handlebar bag. It still "planes" for me, but I am not light (200lbs on most days). I am not sure of these tubes' thickness. It's not necessarily related to thickness, but my Ebisu is pretty light--noticeably lighter than my G2 Kogswell P/R of similar size.

Russ Stringfellow said...

I really like where this is going so far.

I had to laugh when I read Alex's comment. After reading an entry his blog a few months ago I saved a pic of his homemade bike under the name "dream bike."

9/6/9 sounds like a great set for an all-rounder...and I vote for 380.

James Black said...

I have found that bikes with the kind of steering geometry discussed here are prone to shimmy, but I consider this an acceptable downside to having a bike with excellent handling otherwise. My expectation is that an rSogn built with a 73/6.0 front end would shimmy only when there is a front load and while riding no-hands. Some people might object to such shimmy - but I say hey, if you don't want this shimmy, go buy a Surly and suffer the drawbacks of floppy geometry 100% of the time.

alex wetmore said...

Jim: I'm not really sure about the different fork blade options, except that I know my forks used much lighter blades than the original Sogn and the first generation Kogswell P/R. I haven't had trouble with shimmy on my bike at all. I know that experiences on the Kogswell frames have varied.

I think that 385mm AtoC is just right. The original Sogn is a bit long in the AtoC, it is setup to run with fenders over the Neo-Moto. I think that is overkill, those aren't really tires that will work well with full fenders. 385mm leaves plenty of room to run the Neo-Moto fenderless and should give even clearances on the top and sides of the tire. It gives gobs of room to run the Hetre, but won't require more than about 5mm of spacers between the fender and fork crown.

Sean said...

The past several comments and a couple of emails on tubing prompted me to ask how many of us actually will run the Neo Moto at least 50% of the time. I would reconsider the tubing, the geometry to some extent, and the crown/fork if we plan to run the Quasi Moto, let alone the Hetre at most.

Anonymous said...

First let me say, I did go for a ride today, a very very hilly 45 miles in beautiful September weather.

I have been thinking further about the tubing and clearances, with a slightly different outcome:

I wonder in this instance if the 9/6/9 is not leaning toward overbuilt for the “lighter, stripped down Sogn” (I paraphrase.)
I think maybe 8/58 would be robust enough for the great majority of users the great majority of the time. I understand a point can be made about a wide variety of riders on a production frame but a.this is actually a “limited” production, comparatively speaking, b. with the frame tubing specs published, true clydesdales (and how many are there, and in this niche) can go for an overbuilt frame from another manufacturer.

As far as a ding or a dent, I”d rather get one (never have yet) and have a bike that’’s more responsive every time I ride it. The Large could be a 9/6/9.

Another possibility: My BQ came in the mail with the 650B MAP review. Jan Heine seems to have come to the conclusion that the top tube thickness is most critical toward a lively road feel. Maybe the bikes could be spec”d with an 8/5/8 tt.

Finally, while it would be cool to have the Neo-Motos, that kind of turns it into a mountain bike, not an all-rounder.

Mark