#16
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Truly excellent stuff, Dave (and Obtuse) ... really made me rethink things.
Extended a bit, this also helps to explain the thought behind the Terraplane system (if I am not mistaken) - straight round chainstays/bend seatstays. That funky looking rear triangle is suddenly looking a lot more attractive to my old bones and young heart. Last edited by old_school; 03-18-2007 at 08:36 AM. |
#17
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Dave - I think you just pushed my next bike from Ti to Steel.
Obtuse - I think I get what you're saying about the dropouts, but wouldn't some of your concern be alleviated by the axle? Essentially the rear hub (with axle) makes a triangle out of the rear end. Or not. Can someone please educate me here? Thanks, in advance! |
#18
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You are correct in that the rear axle completes the triangle but unfortunately the axles, and more importantly their interface with the dropouts, is pretty wimpy. The 10mm axle standard should go away but I doubt that will happen anytime soon.
If the rear axle was say 20mm in diameter, you could make a very light, very stiff set up. Dave |
#19
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Quote:
I don't know much about this standard, but I think the traditional BB standard should go away too. Cannnondale and Specialized have a larger standard. It seems to me that the new outboard BB bearings and the associated crank designs are full of compromises forced on the component manufacturers to work around a standard size BB shell which came into existence 50 or more years ago. Thoughts on that too? Anyway, this is a very interesting topic. I have also always been told that stiffness comes from the downtube. It is interesting to hear other thoughts on that. This is the reason this is such a good forum. Keep it coming!! |
#20
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I'm not sure I ever equated dt stiffness with drivetrain stiffness.
I have a match Paramount with a big-*** downtube, and slightly bent stays, and the feeling is that there's some flex in the fork and rear end, but the wheels are connected in line. As opposed to some bikes with more of a hinge in the middle. Now, were I to get David or someone to build a custom, I doubt I would specify big oversize tubes like that; enough is enough. But it's not really a bad thing, either. I think the better builders were always wise to the issue of drive-train stiffness (or "snap"). Many would substitute SP chainstays (and dt) on Columbus frames built for competitive riders, who never cared much about weight in those days. |
#21
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Ouestion
Do the oversized chainstays cause (contribute) to the stiffness that gives a bike that "Pocket Rocket" out of gate fast acceleration be it for real or a feel?
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#22
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All this talk about changing standards bothers me.
Considering how little coordination there is between the various players in this game I suspect that changing "the standard" will actually mean no standard, with everyone going their own way 1) as a marketing gimmick so they can claim that theirs is better than the other guy's and 2) so the user (that's us) is locked in to a particular system with no other options. All of this to shave a few more grams (and a very small percentage of the entire system's weight). Louis |
#23
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Dead on the money!!
Quote:
Thank you, thank you, thank you!! For years, I have taught young builders, others in the industry and even competitors exactly what you bring up here. Some got it but most just kept at the down tube fixation. Granted, the down tube can offer a bit of lateral stiffness, but only from the bottom third of it’s length. (Headset bearings do not make much of a fixing point). Yes, down tubes can also offer some torsional help, but they are not very well fixed at their upper end. Chain stays, on the other hand are oriented exactly in plane with a “fixed” structural member (the rear axle). They tend to be relatively short as well, plus there are two of them. What a gift! If one is looking for the ultimate in mechanical efficiency, a straight chain stay is ideal. “The shortest distance between two points is a straight line” and a longer stay is going to be more flexible. As noted, clearances are almost always an issue here though. Joe Breeze used to call chain stays the most dimensionally challenged tubes in a frame. That is what he was talking about. You have to fit the chain stay between the tire and a chain ring somehow. The wider the tube section you can get in there, the better. As others have noted, there have been a number of ways to squeeze things in there over the years. Currently, most manufacturers use some sort of combination of artful bending and ovalizing or dimpling. When Shimano and eventually Campy went from 8 to 9 speed, the front chain lines went outboard, giving us a few more mm to work with. Since then, it has been much easier to use less of whatever clearance technique we were using back in the day. Merlin’s 7/8" stays used to have that curve just behind the chain rings for just that reason. When nine speed chain lines became standard, we switched to straight stays since we had no need to bend them any more. Now, with one inch stays, Merlin and we have taken two somewhat different approaches. Because our frames are all custom, and we know what cranks, rings, tires, etc. each of our customers might be using, we leave our stays straight and dimple only as much as we need to, but no more. Merlin, on the other hand has to satisfy a “stock market.” (Mostly) They do the curving and dimpling thing so that their owners can use Campy 44 tooth rings with large 25mm tires. They also concern themselves with the occasional size 46 foot. Obtuse: Yes, Yes! Rear dropouts are just as much part of the structure. That space between the rear end of a chain stay and the rear axle is very important. Trying to save weight or look cool in there is counter productive. You guys have no idea how happy this thread has made me this Sunday afternoon. Now, I am off to do two hours on the trainer ... Well, you can’t have everything on a Sunday afternoon, huh?
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Tom Kellogg Spectrum Cycles, inc. FRAMEBUILDERS COLLECTIVE Last edited by Tom Kellogg; 03-18-2007 at 12:31 PM. Reason: forgot header |
#24
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Quote:
-Ray
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Don't buy upgrades - ride up grades |
#25
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Very cool stuff ... thanks again to all. |
#26
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I Dave-
jason
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Jason©™® |
#27
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Dave |
#28
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__________________
A man with any character at all must have enemies and places he is not welcome—in the end we are not only defined by our friends, but also those aligned against us. |
#29
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This is a great forum.
I repeat - this is a great forum.
Jim |
#30
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gradient butted, optimized shaping, tire clearance, heel clearance, and stiffness. You can have it all.
__________________
A man with any character at all must have enemies and places he is not welcome—in the end we are not only defined by our friends, but also those aligned against us. |
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