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Dropout concerns

Old 01-29-20, 07:30 PM
  #1  
bikingman
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Dropout concerns

I'm exploring dropout options in BikeCAD, and I've been newly exposed to rocker dropouts. I'm generally pretty impressed with the idea... the hook was "variable chainstay lengths." I'm considering this option on my bike and have since built one into my design (see below). In saying that, I'm concerned with the angle created by the connection between the upper dropout mount and the seat stay. I'm also concerned with a small piece of the dropout mount that sticks out into the rear triangle. I've adjusted the Sy measurement, but can't seem to get it quite flush.

How do others feel about rocker dropouts? Marketing hype or useful for modifying a bike's ride/rear pannier-foot clearance?
Should I be concerned with that dropout angle and how its mount protrudes into the rear triangle?
Does what's below look correct?

Feel free to critisis anything - I'm roughly 6'2 and this bike is just smaller than a 58.

Thanks in advance!

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Old 01-29-20, 09:21 PM
  #2  
Kuromori
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Sliders/rockers are mostly for the ability to have single speed tensioning ability with vertical dropouts or discs, or to minimize wheelbase. Some people use it to minimize the wheelbase when they swap wheels and tires and tuck the wheel in as far as possible. Fewer use it to "tune" the ride somewhere in the middle and think I really wish the chainstay were 3mm shorter. The ability to "lengthen" the chainstay to get the axle under pannier loads is only in reference to the shorter wheelbase you would theoretically be running with the panniers off. It only really matters if getting a 17mm shorter wheelbase with panniers off is worth the hassle of adjusting the dropouts, the high cost of the dropouts, and the weight penalty of the dropouts.

Longer chainstays can do everything shorter chainstays can except maintain that tight wheelbase, so the real question is how important are short chainstays with panniers off to you, not if you want to sometimes lengthen the chainstays for panniers. I see the chainstay on this design is 405mm, and I don't imagine you want to use up half the rocker to run a 397 chainstay. Even if we add the full 17mm to 405mm, 422mm still isn't a great length for panniers. Of course you can pack smaller panniers to keep the weight forward, or join the lowrider front rack cult, and not have to worry about heel clearance or wheelbase at all.

I concede that if you're playing with bent seat tube chainstay lengths, then you might actually fine tune the chainstay length to be as short as tolerable instead of as short as possible. Some people might actually find a +17mm toggle in chainstay length useful as it's not entirely unnoticeable, but this would basically be people that actually bother to move the wheel forward and backwards in horizontal dropouts to tune the ride. Not very many people. 17mm won't get you the range between a tight sub 410mm chainstay, and a 440mm plus pannier happy chainstay.
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Old 01-30-20, 03:01 AM
  #3  
guy153
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I don't think the angle at the top is an issue. Just weld or braze it up and it will be fine.

When you buy regular dropouts they don't make different ones for different seat stay angles. You want to line them up so the hanger is at the correct angle and that often means a bit of a kink where the SS joins.
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Old 01-30-20, 06:59 AM
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The design of those dropouts is focused on MTB usage and the angle between the chainstay and seatstay is 44 degrees, so its no surprise that your 74 degree angle doesn't line up. Its not a problem that can't be fixed by modifying the seatstay connection point. Framebuilding is rarely plug and play, there is a fair amount of metalworking that takes place to make the pieces fit together in a pleasing way. In your case, I would move the stay back some, so its more in line with the rear of the dropout, and reshape the inside curve of the dropout to better match the stay.

Having used these dropouts on several frames, I would advise you to purchase the optional titanium bolt kit. The steel bolts that come with it make it difficult to get enough torque on them without rounding the hex on the head. It takes a lot of torque to prevent the drive side rocker from slipping forward under load. The Ti bolts have a stronger hex and an external 12 point socket head.
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Old 01-30-20, 07:20 AM
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You'll see plenty of slotted stays with the dropout tab protruding out of line. Some of them may be perfectly in line. It's a finishing detail to file the excess points off and blend them in a bit better.
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Old 01-30-20, 08:06 AM
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bikingman
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Originally Posted by dsaul View Post
The design of those dropouts is focused on MTB usage and the angle between the chainstay and seatstay is 44 degrees, so its no surprise that your 74 degree angle doesn't line up. Its not a problem that can't be fixed by modifying the seatstay connection point. Framebuilding is rarely plug and play, there is a fair amount of metalworking that takes place to make the pieces fit together in a pleasing way. In your case, I would move the stay back some, so its more in line with the rear of the dropout, and reshape the inside curve of the dropout to better match the stay.

Having used these dropouts on several frames, I would advise you to purchase the optional titanium bolt kit. The steel bolts that come with it make it difficult to get enough torque on them without rounding the hex on the head. It takes a lot of torque to prevent the drive side rocker from slipping forward under load. The Ti bolts have a stronger hex and an external 12 point socket head.
This is great insight, thanks,dsaul! And thank you for confirming my thoughts on the nature of framebuilding... My thinking was that could file off the tab that's sticking into the rear triangle given the protrusion is relatively small. Actually, I think my excitement of variable chainstay lengths was a bit misguided and this frame may not be the best candidate for this dropout, but I'll address that above below.

Last edited by bikingman; 01-30-20 at 08:24 AM.
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Old 01-30-20, 08:07 AM
  #7  
bikingman
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Originally Posted by Canaboo View Post
You'll see plenty of slotted stays with the dropout tab protruding out of line. Some of them may be perfectly in line. It's a finishing detail to file the excess points off and blend them in a bit better.
Exactly what I had in mind - thanks for confirming this an acceptable practice!
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Old 01-30-20, 08:23 AM
  #8  
bikingman
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Originally Posted by Kuromori View Post
Sliders/rockers are mostly for the ability to have single speed tensioning ability with vertical dropouts or discs, or to minimize wheelbase. Some people use it to minimize the wheelbase when they swap wheels and tires and tuck the wheel in as far as possible. Fewer use it to "tune" the ride somewhere in the middle and think I really wish the chainstay were 3mm shorter. The ability to "lengthen" the chainstay to get the axle under pannier loads is only in reference to the shorter wheelbase you would theoretically be running with the panniers off. It only really matters if getting a 17mm shorter wheelbase with panniers off is worth the hassle of adjusting the dropouts, the high cost of the dropouts, and the weight penalty of the dropouts.


Longer chainstays can do everything shorter chainstays can except maintain that tight wheelbase, so the real question is how important are short chainstays with panniers off to you, not if you want to sometimes lengthen the chainstays for panniers. I see the chainstay on this design is 405mm, and I don't imagine you want to use up half the rocker to run a 397 chainstay. Even if we add the full 17mm to 405mm, 422mm still isn't a great length for panniers. Of course you can pack smaller panniers to keep the weight forward, or join the lowrider front rack cult, and not have to worry about heel clearance or wheelbase at all.


I concede that if you're playing with bent seat tube chainstay lengths, then you might actually fine tune the chainstay length to be as short as tolerable instead of as short as possible. Some people might actually find a +17mm toggle in chainstay length useful as it's not entirely unnoticeable, but this would basically be people that actually bother to move the wheel forward and backwards in horizontal dropouts to tune the ride. Not very many people. 17mm won't get you the range between a tight sub 410mm chainstay, and a 440mm plus pannier happy chainstay.

This is such great insight - thanks, Kuromori. Also, thanks for explaining how these dropouts impact variable wheelbase. It's now clear to me that these dropouts may be useful to adjust the wheelbase length, particularly to allow for larger or smaller tires on the bike. Tire swap could be great for those riding (for example) the divide tour or similar (anyone agree here?). I see the pannier eyelets are actually fixed to the seatstay on this dropout, and any modification to the axle position within the dropout wouldn't have much of an impact on pannier position relative to the rider (thinking of heal to pannier collision here). In saying that, I would like the ability to run a 30mm or perhaps a 32mm wide tire on this bike. If the space isn't available between the tire and the chainstay or the seat tube - this dropout design could be useful. However, I think there're other ways to address this problem without the need for a rocker dropout (perhaps a pinch in the seatstay or a forward offset on the seattube). Feel free to comment on any of this; all this is pretty new to me.
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Old 01-30-20, 09:01 AM
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I think the only good reason to use these is if you have a fixed/ss/internal gear. Changing the wheelbase a little doesn't make them worthwhile. I have some of the older paragon sliders, and I should probably sell them, because I really hate the idea of adjustable dropouts after my experience with Salsa's implementation.

I thought they might have different angles for the seat stays like they do with a lot of their dropouts. But it doesn't appear that they do. And I had to search for them, their new menu structure leaves something to be desired. I would take the seat stays far enough onto the dropout that the tab is just above the outside diameter of the stay. And file off the extra on the inside. Dropouts, as sold, are intended to be adapted to the frame. So they aren't fixed in stone. At least with a tab dropout you can reshape what's there to your requirements. Not so much with a socketed dropout

I think Paragon's dropouts with built in disc mounts are great, you don't really need a fixture for the brake mounts. But I would use one of the fixed length dropouts and ensure clearance for the biggest tires that you might want to use. My understanding is that the short chain stay trend is fading a little. I certainly never bought into it.

My approach to panniers is front lowriders. And bikepacking bags. Rear panniers encourage you to overload the bike, and yet make it really difficult when you have to push that overloaded bike up a hill. Then you can have your short chainstays and the problems associated with fitting both a crank and a big tire. Some of that is fun, if you get it right. Might not be a good first framebuilding project. Use longer chain stays and say you are trying out the Jones style of frame

Last edited by unterhausen; 01-30-20 at 09:07 AM.
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Old 01-30-20, 01:08 PM
  #10  
Kuromori
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Originally Posted by bikingman View Post
This is such great insight - thanks, Kuromori. Also, thanks for explaining how these dropouts impact variable wheelbase. It's now clear to me that these dropouts may be useful to adjust the wheelbase length, particularly to allow for larger or smaller tires on the bike. Tire swap could be great for those riding (for example) the divide tour or similar (anyone agree here?). I see the pannier eyelets are actually fixed to the seatstay on this dropout, and any modification to the axle position within the dropout wouldn't have much of an impact on pannier position relative to the rider (thinking of heal to pannier collision here). In saying that, I would like the ability to run a 30mm or perhaps a 32mm wide tire on this bike. If the space isn't available between the tire and the chainstay or the seat tube - this dropout design could be useful. However, I think there're other ways to address this problem without the need for a rocker dropout (perhaps a pinch in the seatstay or a forward offset on the seattube). Feel free to comment on any of this; all this is pretty new to me.
There's not much drawback to just having longer chainstays or room for bigger tires though unless the short wheelbase handing is really important though. Longer chainstays with wide tire clearance will still fit skinnier tires. The eyelets are already pretty far aft of the dropout, so it does already move the rack back a bit. Typically a rack dropout is placed above the axle, because the relative axle position is important and that allows rack to load the dropout in compression. However the concern with chainstay length is really where the axle is under the load. Depending on the rack and panniers, they can be moved around a bit, but if you move weight behind the rear axle, it starts to negatively affect handling.
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