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  1. #1
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    Trussed bottom bracket, discuss!

    So I know I saw a pic here in the last week or two, someone with a ti frame, 100mm shell, and small trusses running down from the seat tube to the BB.

    Got me thinking, I want them, I've been searching, but I can't find the pics, particularly since I can't recall who made it.Nice work whoever it was, I'd say Jones, but three page deep in search,nothing is jumping out at me.

    Help a brother out, anyone remember the thread?

    Thanks.
    Last edited by MendonCycleSmith; 12-13-2011 at 06:25 AM.
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  2. #2
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  3. #3
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    And a beauty it is.
    Attached Thumbnails Attached Thumbnails Trussed bottom bracket, discuss!-jones-fat-bb.jpg  


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    Last edited by vikb; 12-12-2011 at 11:04 AM.
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  5. #5
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    THAT'S it.

    Thans guys. I think my builder hates me right about now.....
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  6. #6
    Witty McWitterson
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    I love that bike. Wonder if those trusses actually do something. I can see where they may, but DO they?
    Just a regular guy.

  7. #7
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    Since you bring it up Martini....

    I discussed these with Daryl at Form, and he's of the mind that they will make a difference.

    The reason I was seeking that pic was, I've been riding my HT pretty hard over the last few weeks, as an MTB, not a snow bike. As such, hard stomping, standing efforts for climbing, on firm ground, that sort of thing.

    I've definitely found some BB flex going on. I swapped out the Turbine LP's/Phil steel bb I had on it at first, for an E13, and I don't think they were the flex, since it's still there.

    I have a Titus Exogrid HT that Daryl did for me when he was still at Titus,and that does not exhibit the same characteristics, at all. So, knowing that ti does have some give, I'm chalking it up to the 100 mm BB allowing for more levering force when pushed at the extreme end of what my chicken legs can put out.

    So, I saw Jones approach, and am shamelessly appropriating it. Daryl definitely saw the value, and though I don't know what he'll do, I told him I didn't need a *carbon* copy, out of respect for Jeff, but that I felt some trussing would be well worth the added effort.

    So this brings up my discussion point. Several makers out there now have a ti offering. I'll safely assume that they did some on the ground prototype testing prior to bring their rigs to market. Perhaps they were viewing it through the lens of a Snow bike, where one tends to ride more slowly, and efforts are not quite as "power move" oriented as dirt riding might be? It seems easy enough to address in the proto phase, and the solution JJ came up with is elegant, so I can only assume he experienced the same stuff I am.

    Daryl, it seems, has made me his test bunny for the development of their design, and all these incremental improvements should make for a better end product. As he's seeing (along with many of us) folks are riding fatbikes more and more, as all year/condition bikes, so these issues may pop up more frequently as more folks buy ti rigs. Given the chance to negate it now, why would anyone opt to leave it out of their design?

    So, to anyone out there with a ti Salsa, Fatback etc, care to share? Do you find BB flex? I can live with it, it's by no means a ride killer, but given the opportunity to not have it? I'm all over it.

    This isn't meant to be any sort of dig at all the good folks bringing us ti fatty love to date, and if it's an issue for more than just me, and they just didn't realize it could/should be addressed, well, public input can only help the industry make better stuff!
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  8. #8
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    Look close at the Jones design, the seat tube is welded to the down tube for more tire clearance with short chain stays and thus need the bb stays for strength and stiffness. Smart engineering and beautiful fabrication. So this is not apples to apples with a conventional frame.

  9. #9
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    Quote Originally Posted by Bearbait View Post
    Look close at the Jones design, the seat tube is welded to the down tube for more tire clearance with short chain stays and thus need the bb stays for strength and stiffness. Smart engineering and beautiful fabrication. So this is not apples to apples with a conventional frame.
    Nice catch, that is so coool! JJ is da man

  10. #10
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    Quote Originally Posted by Bearbait View Post
    Look close at the Jones design, the seat tube is welded to the down tube for more tire clearance with short chain stays and thus need the bb stays for strength and stiffness. Smart engineering and beautiful fabrication. So this is not apples to apples with a conventional frame.
    Agreed, not quite the same, but from an engineering standpoint, still a valid approach to providing more stability, wouldn't you think?

    After all, I'm not a guy who's all about buying the latest carbon gee gaw because it offers 12% more stiffness than the previous version, but flex you can feel, ought to be mitigated if it can be if you ask me....

    And yes, it is gorgeous work and design, love his stuff, own several of his bars, wish I could get one of his Spaceframes......
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  11. #11
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    Jeff Jones thinks so far outside the box. Gotta love him.

    I dont think the BB shell itself could flex. But the tubes around it can. I guess the wider BB gives you the leverage to worsen this potiential problem.

    I've seen some old steel track frames with triangular sheets wielded in. Like webs. I'm tempted to bring it up with my builder.
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  12. #12
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    Quote Originally Posted by Smallfurry View Post
    I dont think the BB shell itself could flex. But the tubes around it can. I guess the wider BB gives you the leverage to worsen this potiential problem.
    Exactly. What I meant was BB area flex, not the shell itself.

    Yep, I've seen the older track bike "fixes" like what you're mentioning, good catch, and seemingly a good fix to a long standing issue when dealing with ductile materials, pushed to their limits.
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  13. #13
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    it's the whole connection not only the shell that will flex, the wider bb and spindle give a longer moment arm to flex all the tubes around it laterally.
    The real question is.. where are you planning on riding this thing? you'll never notice it at 5 psi on sand and snow. Nates pumped up to 30, clipped in and ripping single track? maybe!?

  14. #14
    Witty McWitterson
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    Hey, I like JJ and all that, but he's not the first to do that forward seat tube idea. ByStickle has been doing it for years. I'm sure that if you dig around the ol' net for a while, one could come up with several older examples of forward thinking like that. Personally, I dig the design. Makes sense to me. That and the plate he uses for the chainstay yoke. Similar thing has been used by Ragley on thier Ti bikes.
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  15. #15
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    In Theory;

    In a conventional setup where the Seat Tube, Down Tube and Chain Stays attach to the BB in separate locations, my guess is that the crank forces would enter an axial load (side to side, perpendicular to the frame) into the ST and a radial load (twisting) into the DT. I would think that this may put a large load on the weld joint at the ST. In the case of the Jones frame - which is indeed nifty - there is a radial load in the DT, but that is a very small area as it interfaces with the ST very close by, where it would enter an axial load into it.

    I wonder if they added these braces on the Jones based on a perceived or realized need? Was it because they lacked the triangulation of two tubes joining there? Did they model it or just take an educated guess? Are the two designs 6-of-one and dozen/2 of the other in terms of BB flex?

    It would be very interesting to see some stress analysis of both conventional and Jones layouts to see the result. As a baseline, I can fully envision a 100mm BB adding twist to a frame, and it would seem a good idea to take this into consideration. I'd be a bit surprised if they hadn't. When I do find myself enjoying my own Fatbike in the future (hopefully not to far off), I intend to do so in all seasons and conditions, so it would be nice if it were designed to take it!

  16. #16
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    Quote Originally Posted by Bearbait View Post
    it's the whole connection not only the shell that will flex, the wider bb and spindle give a longer moment arm to flex all the tubes around it laterally.
    The real question is.. where are you planning on riding this thing? you'll never notice it at 5 psi on sand and snow. Nates pumped up to 30, clipped in and ripping single track? maybe!?
    Maybe we just missed each other, but yes, agreed, it's not the shell itself flexing. That said, bracing it in such a manner would be quite akin to standing with your legs together, and being pushed from the side, versus standing with legs apart, you're much more stable spreading the load over a larger area.

    I'm no engineer, so I may be missing something, but it makes sense, doesn't it?

    This is kinda the whole reason I bring it up. The industry till now, has been predominantly snow/soft condition based as far as product design and development. Riders praise the Endo for its float, but it's a sucky traction design, particularly when compared to the newer designs, put forward to solve the issue of riding in conditions other than just soft. Apparently, folks want more fatbike versatility, no?

    Ditto for the frames. Sure, while Salsa, et al make bikes designed for snow riding, the Pug is designed to ride like an MTB. My new rig is too. Others designs going forward, will likely fall into a more broad based use, than just snow, since that base is covered pretty well already.

    Since snow riding is very different, yes, it's likely you'd never notice BB area flex on a ti Salsa or Fatback.

    Interesting to note, Mikesee at one point said he's sworn off fat tires for anything but snow. Doesn't see enough, if any, advantages. Heavier tires/wheels, and all that. He's also not personally interested in tubeless, which is now coming on strong as well. All good, I hold him up as a pioneer, at least inasmuch as he shares his thoughts well and frequently, but he also, speaks for himself, not the fat community as a whole. I think we're pretty varied, and growing by the day.

    For the riding I'm doing, tubeless set ups are still heavier than say an Arch with a Racing Ralph, but not by so much that I'm avoiding the bike,not at all. The massive contact patch gives a significant increase in traction in certain areas. I'm not running my Nates at 30 (that would suck monkey butt, holy pogo stick!!!), it's more like 8. And I am ripping singletrack as fast as I can, easily as fast, if not faster, than on any of my 29ers. The soft blobby tire hooks up over gnarly nasty rootballs, span rock garden gaps with confidence increasing fashion, flows over the muddy sections without sinking as deep as the skinnies, yeah, I find it to be a huge improvement.

    Another tool in the box if you will. Sure, I still reach for my SS, FS or HT for some stuff, but more just to mix it up, than one bike being far superior for a given situation, over the fat.

    So, I'm guessing I won't be the only guy in the world, who reaches for their fatty for a variety of rides, not just sand and snow. That being said, and I think you'd agree, a stiffer BB area isn't a bad thing for those types of rides.

    So, if my "findings" can help anyone out there, build a bike better suited to a broader range of riding that their bikes will likely start to see, cool!

    I am curious, I'll assume there's some ti riders out there now, am I alone? You guys only ride soft stuff? I'd have a tough time saying no to a bike as cool as a ti fatty, when hitting the singletrack for some high speed smile making
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  17. #17
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    Quote Originally Posted by TrailMaker View Post
    In Theory;

    In a conventional setup where the Seat Tube, Down Tube and Chain Stays attach to the BB in separate locations, my guess is that the crank forces would enter an axial load (side to side, perpendicular to the frame) into the ST and a radial load (twisting) into the DT. I would think that this may put a large load on the weld joint at the ST. In the case of the Jones frame - which is indeed nifty - there is a radial load in the DT, but that is a very small area as it interfaces with the ST very close by, where it would enter an axial load into it.

    I wonder if they added these braces on the Jones based on a perceived or realized need? Was it because they lacked the triangulation of two tubes joining there? Did they model it or just take an educated guess? Are the two designs 6-of-one and dozen/2 of the other in terms of BB flex?

    It would be very interesting to see some stress analysis of both conventional and Jones layouts to see the result. As a baseline, I can fully envision a 100mm BB adding twist to a frame, and it would seem a good idea to take this into consideration. I'd be a bit surprised if they hadn't. When I do find myself enjoying my own Fatbike in the future (hopefully not to far off), I intend to do so in all seasons and conditions, so it would be nice if it were designed to take it!
    Thanks for the thoughts. Your verbiage/engineerese is far better than mine

    I'd suppose the loading to be quite different on JJ's bike, so it would be an important consideration in his case. I'm curious if he dealt with it because he found without them, an exaggerated version of what I'm feeling, was noted....

    I'm guessing that the designers to date have found the current design sufficient as is (as I do too) and in aluminum, it's likely less noticeable still.

    Steel, particularly in say, a Pug, utilizes a bit beefier tube set, and steel is known to be less flexible than ti as a material. Not a huge difference, but it's not the first time someone has said ti flexes more than steel, putting aside factors like diameter, build design, butting profiles etc.

    That said, if nobody is noting it in their steel frame, why bother. If it's just me with my Form, I'll fix it for my use. But if you spend a ton more $ to buy ti, then discover you want to use the damn thing all the time, I'd think it'd be appreciated to have this aspect taken into account, that's all I'm getting at.
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  18. #18
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    I have a Carver sourced Ti Fatback. I ride it all seasons. Don't notice any BB flex to speak of but I tend to keep tire pressure as low as I can. I weigh about 170 on the bike for what that is worth.
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  19. #19
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    Quote Originally Posted by sryanak View Post
    I have a Carver sourced Ti Fatback. I ride it all seasons. Don't notice any BB flex to speak of but I tend to keep tire pressure as low as I can. I weigh about 170 on the bike for what that is worth.
    Thanks for the input, 100 mm BB shell? Cranks?

    I run into this a lot it seems. I had a belt drive, properly set up too, according to all input, tools etc. I could skip the thing badly, going up local hills. Made me nuts, took it off due to that. I don't consider myself an overly high output/strong rider. Average at best, I'm no Hercules. No racing, no training, no weights, I just ride several days a week. Weigh around 175. I don't consider my hills to be that much steeper, the riding more technical, etc etc etc. Just a guy who likes to ride.

    Yet I experience, or notice these things in certain situations, with certain products, not others, so I know I'm not making things up.

    You never feel the pedals kind of falling away under your feet under hard efforts up hills? Awesome if not. I just don't think I'm that much of anything, more than the average rider is all....
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  20. #20
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    I'd guess the main difference to be that you are open to new ideas, and more perceptive (relative to the average joe) to what's happening since you're in the midst of designing a frame, experimenting with different fat configurations, etc...

    That, and most riders these days don't/can't notice their bike because of the iphone/pod hoovering up what's left of their dwindling attention span...

    MC

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    you want some wussy small tubes from the seat tube to outer edges of 100mm bb or some manly box gussets joining the seat tube (which is welded to the downtube) to the bb and the chainstays?
    they could act as giant anti-chainsuck plates!!! FWOAR!!

    (and mikesee would hit a park tool in the non-drive stay I'm sure)

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    I like it, but I wouldn't want it to interfere with using the direct mount adapter. I prefer it over e-type.

  23. #23
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    on my pugs i notice that bb flex if you will. the metal guide of the front derailleur is super close to the tire and when i stand up and stomp hard you can hear it move in and rub the tire. seems like maybe i could use some trusses! ive heard of them for axles and for roofs but never bikes...

  24. #24
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    my guess is this is a hard thing to isolate and a bit subjective.
    who knows.. someone should weld some gussets on a pugs and do a blind test.

  25. #25
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    Hmmm. Make a cheap extensometer - 2 lengths of small tubing that telescope together, hose clamp to BB shell and seat tube (along the line of those sweeeeet Ti braces). Put an oring on the smaller one. Go ride. See how far the oring has moved - just like on your airshock.
    This isn't a "you're doing it wrong" topic.

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  26. #26
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    When I had my last bike built I specified the lightest tubeset I could get away with. The bike is a rocket ship and climbs great. The idea that flex is a bad thing is an error in how we think about bicycle design. I'm not well versed enough to design a great bike, but I do know that making the bike stiffer isn't a goal I'd go after in general.

    If you've had a problem with frame flex in terms of how the bike handled or some other negative consequence I'd talk to the frame builder about how to address it. If you've just noticed you BB area flexing a bit under hard efforts I wouldn't do anything at all.

    Bicycle Quarterly did a series of articles about frame flex and in their blind tests riders consistently preferred the more flexible bike frames. When they didn't know which bike was which and just had to comment on the ride experience and their time on a fixed route.

    That's not to say you want crazy ultralight tubing if you are 250lbs and hammer like a freight train. The design of the bike needs to address your needs including such things are how much you weigh, how aggressively you ride, how much stuff you plan on carrying and what terrain you plan on riding.
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  27. #27
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    Quote Originally Posted by MendonCycleSmith View Post
    Thanks for the input, 100 mm BB shell? Cranks?

    You never feel the pedals kind of falling away under your feet under hard efforts up hills? Awesome if not. I just don't think I'm that much of anything, more than the average rider is all....
    100 mm BB with Race Face square taper BB and Middleburn cranks, Candy pedals if it's above zero and some big Welgo platforms when it is cold. I have a Ti fork and there is enough flex in that that you just wouldn't see anything else. Seriously though I have not felt the pedals falling away under my feet. I have a 1949 Paramount built with small diameter tubes and that baby flexes, so I think I would be able to tell if the pedals were flexing overmuch on the Fatback.

    Also how do you fit a front derailler around the struts?
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  28. #28
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    I hate BB flex. I reckon it sucks the life out of you. Or maybe I'm so feeble that I can't spare any watts for bending the frame back and fore.

    As for not being able to tell the difference, I'm not so sure. I've got 2 track bikes (used on road), one a nice steel one, and the other an alloy frame. The moment you hit the pedals for anything like a hill the alloy frame responds instantly while you can feel the steel one winding up. I think the front fork has more to do with the feel of the bike (comfortwise) than the BB.

    I'll go for a braced BB any day.
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  29. #29
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    Quote Originally Posted by vikb View Post
    When I had my last bike built I specified the lightest tubeset I could get away with. The bike is a rocket ship and climbs great. The idea that flex is a bad thing is an error in how we think about bicycle design. I'm not well versed enough to design a great bike, but I do know that making the bike stiffer isn't a goal I'd go after in general.
    Quote Originally Posted by Velobike View Post
    I hate BB flex. I reckon it sucks the life out of you. Or maybe I'm so feeble that I can't spare any watts for bending the frame back and fore. .
    IMHO the effect of BB flex is, to a degree, a matter of taste. I can bend the hell out of my steel track bikes BB area. But its part of the bikes ride. A ride I very much like. I also have a speed focused BMC racemaster, with a massively overbuilt alu BB cluster. If you so much as tense your legs during a fart on this bike. It leaps forward. I love the ride of this bike too.

    My instinct is to prefer the softer option for a fatbike. In the same way you may want more stable steering. But like I said its a matter of taste. Nobody likes a noodle though.

    My current thinking, is that having the chainstays join the BB shell as far apart as possible. Without fouling the cranks. Could be a neat solution to the problem of increased leverage.
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  30. #30
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    Great thoughts one and all, much appreciated.

    How'd MC know I don't ride with an iPod?

    So here's where I'm at. I'd agree with Bearbait that's kinda tough to isolate, except I have a ti frame from the same hands, with a 68 mm BB shell, and this feeling doesn't occur there, so it wold have to be the wider shell, no?

    Glad would be the wrong word, but its heartening to hear that stoney bones has a Pug and can feel it. Simply points out the need across the board (possibly) for a subtle tweak in design philosophy, should any builder care to consider it...

    I'd agree, some may not care a stitch about BB region flex, but if a frame was a few grams heavier, and sold to all, would you object to it NOT being there? I'm thinking not?

    I know for me, as I think I said earlier, it doesn't ruin my ride, but not having it on most bikes, then having it on this one, it's kinda like a little pebble in your shoe, you can still walk fine, but you still want it out of there....

    Thanks for bringing up the FD clamp, I do run one of the direct mount Problem Solvers clamps, so that will need to be considered. I'mvery curious to see what sort of solution Daryl comes up with, perhaps it'll be some massive Brooklyn Bridge, monster truck gusset thing that works as a chain suck device with park tools installed, who knows?

    And yes smallfurry, wider the chainstays are set, the less it should flex, which only points up more, the need to stabilize the design if possible.

    Wadester, if I could envision what you're getting at, I'd do it, if only because I know you love gadgets

    vikb, The rest of the bike is rock solid, at least to me. And I'd agree, sometimes, in some areas, flex is beneficial. This bike? It's a soft tail, so flex is very much desirable there! And I agree, as someone who works in the industry, I'm really tired of manufacturers trying to upsell everyone every year with the promise of a stiffer bike. That's a way to sell more units. Don't worry sir, your Trek Madone from last year is way stiff enough for you to be competitive inthe club race this weekend.

    This isn't about that at all. The wider shells introduce a mechanical advantage, that I think for many, created a "problem" they didn't bother to be bothered by since the bikes are so freakin' cool all on their own. The way the originators rode them, they likely never even noticed it. I loved my purple Pug as it was, slippery, poor cornering, braking Endos and all. But I really love the way the newer tires make it ride, even more.

    If I, as an average (or less even) strength rider can pick up on it when riding my bike as I would any other bike I own, it would seem that if there's a simple way to fix it I'd be crazy not to try to bring it to light so we all can discuss it, and so the designers who frequent this board can tweak stuff if they feel there's enough cause to warrant the change. Just like how they heard us, and now we have Nate.
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  31. #31
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    If you built these into the frame, it seems like a no brainer to incorporate iscg tabs into the crank side gusset or tube.

    For this application, I suspect a triangular gusset would have a better strength/weight tradeoff than a tubular brace like on the Jones bike.

  32. #32
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    Quote Originally Posted by MendonCycleSmith View Post
    Great thoughts one and all, much appreciated.

    Wadester, if I could envision what you're getting at, I'd do it, if only because I know you love gadgets
    But it's so clear in me head!
    First, a definition: "An extensometer is a device that is used to measure small/big changes in the length of an object. It is useful for stress-strain measurements and tensile tests. Its name comes from "extension-meter"."

    Second: The last couple of FS bikes I bought had air shocks - and came with an oring on the shaft, just sitting there. If you moved the oring up against the air chamber before a ride, you could see how much compression you got out of the shock.

    Third: Combine the two. Get 2 pieces of small telescoping tubing Metal Shapes, Brass, cooper aluminum Tubing, strips, sheets, channel, angle, and rod - I'd get 3/32&1/8 brass, but that's me. Cut a section of each about 2/3 the length from the outer end of the BB shell to the seattube (45 degrees angle). With a small hammer, mash an end of each to match the radius of the frame surface. Slide an oring onto the smaller tube, slide the tubes together, then clamp the formed ends to the frame. It will look like the tubular gusset Mr. Jones made - but in use, any movement of the frame will push the oring away from the overlap of the telescoping tubes. Only measures compression, but still. Then you get an actual deflection - if there is one.

    Last: Apologies for length of geek-out.
    This isn't a "you're doing it wrong" topic.

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  33. #33
    Dr Gadget is IN
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    Oh yeah! And as a comment for making the brace and not interfering with a derailer:

    Remember that symmetry is overrated. Brace the non-drive side, and leave the derailer area open. You know - a LeftyBrace?
    This isn't a "you're doing it wrong" topic.

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  34. #34
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    Hey Craig,

    What's the diameter of those chainstays? My micrinterwebometer says 3/4" but it's not terribly accurate.

    There's a lot going on in the BB area of a bicycle. It's generally accepted that the diameter of the DT and chainstays have the biggest effect on BB twist and it looks like you already have a beefy DT on there (1.75"?)
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  35. #35
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    Quote Originally Posted by wadester View Post
    Oh yeah! And as a comment for making the brace and not interfering with a derailer: Remember that symmetry is overrated. Brace the non-drive side, and leave the derailer area open. You know - a LeftyBrace?
    Exactly what I was thinking;

    It would likely do the same job as two of them, given proper sizing. It doesn't take much of a brace to effect a large increase in node (where tubes intersect) stiffness. One corner gusset can offer as much as a 20-30% increase in node stiffness over having nothing. In the cage below, I was dealing with some portions of a pre-existing cage, so the node is not as closely grouped as I would normally make it. The gussets help make up for that.

    Another thought is that a tube would also tend to be less of a crud catcher on a BB than a gusset, it seems to me.
    Attached Thumbnails Attached Thumbnails Trussed bottom bracket, discuss!-dancage2large.jpg  


  36. #36
    Hybrid Leftys aren't real Moderator
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    Quote Originally Posted by smudge View Post
    Hey Craig,

    What's the diameter of those chainstays? My micrinterwebometer says 3/4" but it's not terribly accurate.

    There's a lot going on in the BB area of a bicycle. It's generally accepted that the diameter of the DT and chainstays have the biggest effect on BB twist and it looks like you already have a beefy DT on there (1.75"?)
    They are 3/4, good eye.

    Measured my Titus, they are 7/8", but are ovalized at the BB, whereas the Form is round, right to the BB.

    DT's on both are the same, 1 3/4".

    Gotta be more than ovalized stays making the Titus not move, but I've ben wrong before.

    Wadster, you're worried about geek out length, when you're talking to ME?

    Thanks for the info, I may play with that, but it will only bear out what my body's telling me already

    Lefty brace, hmmm, yeah, 'bout that. Forks, I dig asymmetry, not so much with BB bracing. Did the measurements, I have gobs of room for any range of possible designs, even with the FD in the 22T.

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  37. #37
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    MSC...for a little different aproach than Jeff, take a look at Wolfhoundcycles.com

    Fred uses a split seat tube joined to the BB.

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