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Chainstay Orientation

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Chainstay Orientation

Old 12-03-19, 04:51 PM
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liverunbike
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Chainstay Orientation

Pardon my ignorance, but has anyone toyed with the idea of altering chainstay orientation in the quest for vertical compliance and lateral stiffness?
Specifically, I've attached what I'm thinking. These are just sketches, but accurately reflect a standard 68mm BB shell and 30-16 chainstays.
Has anyone messed around with something like this? Would any of these be more likely to work than others?
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Old 12-03-19, 06:18 PM
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It just wouldn't work, because you still have to fit a tire between the stays. You can make them as wide as you want at the bottom bracket shell, but they have to become narrow enough to fit a tire about 2 inches away from the shell. That "laterally stiff and vertically compliant" stuff is mostly marketing BS. You can make the chainstays as compliant as you want, but they can't move in the vertical plane once you attach the seat stays. A triangle is just not a flexible structure.
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Old 12-03-19, 07:16 PM
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Some builders claim that 22.2 round stays are stiffer laterally than 16x30. If there is a difference it can't be much but just say'n.
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Old 12-03-19, 08:05 PM
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I've seen what looked like round stays on cheaper department store bikes from years past. Sears? Dutchess?

However, I agree with @dsaul, that the vertical orientation gives the best strength, plus best tire/crank clearances (sometimes also dimpled). And, still all fitting on a standard width bottom bracket.

Of course, an alternative would be going with more stays like a Mixte.



Some tandems have also used a triple stay design, although not as common with a parallel top tube.

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Old 12-03-19, 08:16 PM
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Oh, you can add some complex curves to chainstays for tire/crank clearance, although you still have the same Q-Factor and width restrictions.

Yokes?

https://www.paragonmachineworks.com/...stay-yoke.html



Whew, not cheap.

I presume curved stays aren't quite as stiff as straight, but don't seem to be a major problem either.
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Old 12-03-19, 10:08 PM
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the real pinch point is at the chainrings and tire on the drive side. I guess that's why dropped/elevated stays have come back. Almost all chainstays were 22mm round until sometime in the '80s, but I wasn't paying attention when oval stays showed up. Some people use bigger round stays than that now, 7/8" maybe?
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Old 12-06-19, 05:41 AM
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There's an FEA by Damon Rinard you can find on the Sheldon Brown website done years ago which is very interesting. The bottom line is that the frame is already really stiff in the vertical plane anyway because that's where all the tubes are triangulated.

As others have said the flat bit is for chainring/tyre clearance. A lot of chainstays however are flat all the way to the BB shell and this seems a bit pointless as you're adding stiffness in the direction where it's already really stiff and reducing lateral stiffness. I like the "ROR" ("Round/Oval/Round) chainstays that both Columbus and Reynolds make in road-bike sizes. These are round where they join the BB shell, then have a squashed bit for the tyre, and are then round again.

You could realize your design by buying some ROR chainstays and squashing them again at the BB end in the vice but at 45 or 90 degrees to the original flat bit. It might look rather distinctive and even be easier to get the TIG torch down in there.
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Old 12-06-19, 02:16 PM
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The stiffest feeling frames laterally have either had super beefy chainstays such as a Tesch S-22 1.125" at the bottom bracket, and squashed where the tire and chainring (42t) would pass, and the Masi 3V with the 25mm chainstays, slightly oval for the same reasons behind the socket.
One could in a fillet brazed mode, tilt the oval stays to possibly help IF you don't get yourself in clearance trouble. The original diagrams are exaggerated I think. I would try the lower right diagram so modified.
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Old 12-07-19, 10:55 AM
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since there is never anything new in bicycle design, I'm almost positive there have been bikes with oval chain stays with the flatter axis oriented vertically. I'm not sure how to do a google image search that would find such a bike, but I'm pretty sure I have seen pictures. If you also had Hetchins-style bent seat stays, you might actually get a few microns of flex in the rear triangle.
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Old 12-07-19, 11:32 AM
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The best "modern" example of taking advantage of a chain stay's orientation for flex is hingless rear suspended stuff that use a flat plate, horizontal WRT the ground, as the stay yoke. I forget who but I remember someone doing this in Ti. Andy
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Old 12-07-19, 11:58 AM
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Benotto used a diamond shaped chainstay on some of their frames. It is still taller than it is wide. It is hard to capture in photos.

Here is an example:
Benotto 3000 1978 restauration - Le Cycleur



I think the idea was similar to the Colnago Master and related frames. The diamond shaped tubes to increase both vertical and lateral strength.

These tubes seem to have a point on the inside, but a similar design might be a triangle shaped tube that was flat on the inside, and pointed on the top, bottom and outside.
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Old 12-07-19, 12:08 PM
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if riding a mountain bike has taught me anything, it's that you don't really want all that much vertical compliance in the frame unless you are hitting big rocks. I know people that use suspension seat posts on their gravel bikes, which seems like a good solution. I have never really wanted a road bike to have more vertical compliance in the rear triangle. The fork, maybe, but the best solution for that in my mind is bigger tires. The whole "horizontally stiff, vertically compliant" thing seems to have been questionable in the first place. Lots of people like a bit of spring in the horizontal direction, describing very stiff bikes as feeling dead.
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Old 12-07-19, 10:27 PM
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[QUOTE=unterhausen;21236682]if riding a mountain bike has taught me anything, it's that you don't really want all that much vertical compliance in the frame unless you are hitting big rocks. I know people that use suspension seat posts on their gravel bikes, which seems like a good solution. I have never really wanted a road bike to have more vertical compliance in the rear triangle. The fork, maybe, but the best solution for that in my mind is bigger tires. The whole "horizontally stiff, vertically compliant" thing seems to have been questionable in the first place. Lots of people like a bit of spring in the horizontal direction, describing very stiff bikes as feeling dead.[/QUOTE

Back in the day we called this "resiliency" and it was a positive feature thin walled frames had, compared to the relatively thicker walled stuff. But the tools to sell bikes changed with competition becoming the number that mattered. Andy
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Old 12-08-19, 02:55 PM
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Originally Posted by unterhausen View Post
since there is never anything new in bicycle design, I'm almost positive there have been bikes with oval chain stays with the flatter axis oriented vertically. I'm not sure how to do a google image search that would find such a bike, but I'm pretty sure I have seen pictures. If you also had Hetchins-style bent seat stays, you might actually get a few microns of flex in the rear triangle.
The early SuperSix Evos did something like this, but ran into problems because they didn't work with wider tires/rims. The following articles have some pictures of how they were shaped.

https://www.velonews.com/2011/05/rev...six-evo_171341
https://road.cc/content/news/155494-...oad-bike-video
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Old 12-09-19, 07:19 AM
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Originally Posted by Andrew R Stewart View Post
The best "modern" example of taking advantage of a chain stay's orientation for flex is hingless rear suspended stuff that use a flat plate, horizontal WRT the ground, as the stay yoke. I forget who but I remember someone doing this in Ti. Andy
I'm sure there have been more than one builder doing this, but I remember seeing a TiCycles example back about 8 years or so.
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