# Wishbone stays?



## IvanDobski (Jul 30, 2009)

What are the practical benefits (or otherwise) of using a wishbone stay design?

I'm putting a build together and prefer the look of theses but not sure if theatres any other value in it?

Cheers


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## restlessrider (Nov 29, 2007)

I'm not aware of a structural benefit, but in a production environment it is easier and faster to miter a single tube to the ST than two separate tubes (of course you have to first make the monostay sub-assemblies). I remember Bontrager saying he used monostays because they simplified production - and they could use the same sub-assembly for any size frame, just cut the excess 'mono' tube and weld.


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## jgerhardt (Aug 31, 2009)

I always wondered why my Dad's old Bontrager had the wishbone stay. I guess it also eliminates the need for a chainstay brace. There has to be some drawbacks to it, or you would see more of them. I could only assume that it would not be as rigid as a fastback with a chainstay brace?


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## rustola (Jan 15, 2008)

One of the 'historical' benefits of wishbones is for cantilever brakes - they don't flex as much under hard braking, as the wishbone part tends to resist tube torsion.


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## pvd (Jan 4, 2006)

Wishbone stays are really lame. Almost the worst way of doing things. They offer no mechanical advantages traditional systems and fall short in many ways. They are used by lazy framebuilders interested more in cheap production than the best design. Traditional triangulated stays with bridges are the best way of doing the rear end, but offer more challenge in placing the bend for each size frame.


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## laffeaux (Jan 4, 2004)

With disc brakes, there may not be any advantage to a wish bone stay. However, as Rustola said, when cantilever brakes where common the wishbone design was used to prevent the seat stays from flexing under hard braking.

Keith Bontrager was a big proponent of them. According to him it reduced brake flex without adding weight to the frame.


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## smudge (Jan 12, 2004)

restlessrider said:


> I remember Bontrager saying he used monostays because they simplified production - and they could use the same sub-assembly for any size frame, just cut the excess 'mono' tube and weld.


That's exactly it. Once I realized this, I thought it was genius.

A good friend of mine has a letter from Raleigh framed and hanging on the wall of his office. It was written in the 70's and was essentially a "no thanks, we don't need an apprentice" letter. The best line in there was something like this, "figure out how you want to build a bicycle and then make up whatever technical B.S. you want to help you sell them"


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## j-ro (Feb 21, 2009)

I can attest to the claims of enhanced braking from the wishbone set up.
With the studs on the reverse curve of my setup, rear brake action is instant, solid and doesn't fade.
There are some cast wishbone crowns available that are downright wispy.
They are drilled for a regular road type brake which throws the braking benifts thing right out the window.


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## smudge (Jan 12, 2004)

j-ro said:


> I can attest to the claims of enhanced braking from the wishbone set up.
> With the studs on the reverse curve of my setup, rear brake action is instant, solid and doesn't fade.
> There are some cast wishbone crowns available that are downright wispy.
> They are drilled for a regular road type brake which throws the braking benifts thing right out the window.


For the record, yours DEFINITELY doesn't appear to be easy to manufacture. I was thinking Moots, Dean and Bontrager. They could bang out hundreds of assemblies and they're identical for every size frame save for the top miter.


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## j-ro (Feb 21, 2009)

smudge said:


> They could bang out hundreds of assemblies and they're identical for every size frame save for the top miter.


yeah, it's always someone else with the good ideas. I think that's how Hunter does his, seems clean and fast.

I guess my hooptie really isn't a wishbone persay but the comment about them resisting flex was pretty relevant to it so I threw it out there. It does make a difference in CCX. After that I can't think of much that uses cantis or V's anymore.


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## pvd (Jan 4, 2006)

You guys are seriously smoking crack if you think that a wishbone stay has any advantage in reducing brake flex. It's just not true. In fact, they are typically worse. How can you all not see this? The ability of a triangulated stay configuration to support the loads of the system are far far superior.

Wishbones are just discusting junk. Simple enough.


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## j-ro (Feb 21, 2009)

Aesthetic opinions aside,(which I have no problem with) How would you explain this entire subset of bicycle component manufacturing; brake booster
It would appear that it's attempting to turn a triangulated system into a....................wait for it..........Wishbone!

Seriously though Pete, if you were to cut my hooptie off below the studs and try to straighten it by pulling it apart you would never move it. The concavity of the stay before it loops around makes it super strong. 
If you were to do the same with a triangulated set you would be able to make them move.

BTW, don't you design a bike with a wishbone for your homies in Boston?


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## tamen00 (Mar 10, 2004)

I was considering a super high end ti mountain bike frame from a new company in Boston that is doing some cool frames with wishbones... but now that Pete has chimed in and stated that "Wishbones are just discusting junk." I am having second thoughts.


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## Walt (Jan 23, 2004)

*No, it's not*

I don't use rim brakes for anything, ever, so I don't have much to say on the brake-flex front, but I'm pretty sure the "Brake booster" devices are intended to reduce the flex of the bosses themselves/seatstays twisting (ie, the booster bolts on top of the brake so that the brake boss can't flex in at the top).

I could be wrong. In any case, I don't think there is anything particularly wrong with either way of building seatstays. They will both ride just fine and you'll forget about which type you've got soon enough once you're on the trail.

-Walt



j-ro said:


> Aesthetic opinions aside,(which I have no problem with) How would you explain this entire subset of bicycle component manufacturing; brake booster
> It would appear that it's attempting to turn a triangulated system into a....................wait for it..........Wishbone!
> 
> Seriously though Pete, if you were to cut my hooptie off below the studs and try to straighten it by pulling it apart you would never move it. The concavity of the stay before it loops around makes it super strong.
> ...


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## pvd (Jan 4, 2006)

I am not a part of that company. I have helped them with some design work and that is all. Their bikes are theirs. I share my opinions but they are the ones with their names on it.

Regarding brake boosters. They are an important part of any cantilevered brake system. I used them before 1998 (disk era begins) and still have one on my 24" cruiser. The job of the booster is limited to supporting the tops of the canti boss from spreading. That is all, a simple arch. The stays will support the bottom of that boss but more importantly be the structure supporting the rear wheel and rider. Because of this a design that works even better is available, the triangulated end. How is this not clear?


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## NorseRider (Feb 9, 2004)

smudge said:


> That's exactly it. Once I realized this, I thought it was genius.


Ditto. The whole rear end of the Bonty's are a true feat of engineering from a production standpoint. Modular and super simple sub-assemblies all the way.

Truls


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## Meriwether (Jul 26, 2007)

*they look cooler*

i've done a few wishbones on my personal frames and I just like how they look. If for no other reason, I was under the impression that wishbone stays would be stiffer because the tubes used are typically thicker-walled (0.9 instead of 0.6)...? But I do see what you are saying PVD about a rear triangle being stiffer or stronger when connected by two points instead of one (?).







I'm sure few could ever tell the difference while riding, BUT Wikipedia says they're stiffer so it must be true 
_"Another common seatstay variant is the wishbone, single seat stay, or mono stay,[16] which joins the stays together just above the rear wheel into a monotube that is joined to the seat tube. A wishbone design adds vertical rigidity without increasing lateral stiffness, generally an undesirable trait for bicycles with unsuspended rear wheels.[17]"_
The reference cited is:
^ Van Der Plas, Rob, (1995). Bicycle Technology (3rd ed.). Bicycle Books, San Francisco. pp. 62. ISBN 9780933201309.* "Used on a bicycle with unsuspended rear wheel, the wishbone seat stay actually adds rigidity in the wrong direction - vertical rather than lateral stiffness."*
I don't know the methods of this guy's testing, but it doesn't say they are *less* rigid in the 'wrong' (lateral) plane...just that they aren't *more* rigid in that plane.


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## jtmartino (Jul 31, 2008)

pvd said:


> The job of the booster is limited to supporting the tops of the canti boss from spreading. That is all, a simple arch. The stays will support the bottom of that boss but more importantly be the structure supporting the rear wheel and rider. Because of this a design that works even better is available, the triangulated end. How is this not clear?


A large number of the lightweight racing bikes from the 90s would experience seatstay deflection under heavy braking. I've seen it in person on a few of my own bikes - the seatstays themselves are pushed away from the rim when brakes are applied.

I'm a fan of the Salsa Arc de Tri-oomph. Great retro boosters that work well.


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## xmessenger (Aug 13, 2010)

I own a 92 Rocky Mountain with the wishbone seatstay and thought that there may be some advantages both for braking(cantilever) and possiblt frame strength. The former due to the larger diameter tube upon which the bosses sit would be less inclined to twist or bow out, and the latter due to the fact that there is only one large tube being welded to the ST as opposed to two smaller tubes and therefore less HAZ involved at the junction. Perhaps the triangle is a superior geometric design on paper but in reality you are using weaker tubing and increasing the HAZ dramatically if you include the welded bridge. Of course this all depends on the type of wishbone and type of A stay but in a purely general sense I do not see the weakness in this design. Lets not forget, Keith Bontrager is no dummy when it comes to design, and his bike were known for their strength. I'm not an engineer or a bike builder but from what I do know regarding tube diameter and the inherit weakening involved with welding thin tubes I fail to be convinced that the wishbone design is inferior outside of personal aesthetics.


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## Fillet-brazed (Jan 13, 2004)

j-ro said:


> Aesthetic opinions aside,(which I have no problem with) How would you explain this entire subset of bicycle component manufacturing; brake booster
> It would appear that it's attempting to turn a triangulated system into a....................wait for it..........Wishbone!
> 
> Seriously though Pete, if you were to cut my hooptie off below the studs and try to straighten it by pulling it apart you would never move it. The concavity of the stay before it loops around makes it super strong.
> ...


Got the link for this thread from a semi-current VRC thread.

The round shape on a brake booster has nothing to do wtih trying to make it like an arch or like a monostay. A brake booster would be a much stiffer (and better) brake booster if it went directly from one brake boss to the other, but it can't because the tire/wheel is in the way, so it must go around and the result is an arch.


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## jtmartino (Jul 31, 2008)

Fillet-brazed said:


> Got the link for this thread from a semi-current VRC thread.
> 
> The round shape on a brake booster has nothing to do wtih trying to make it like an arch or like a monostay. A brake booster would be a much stiffer (and better) brake booster if it went directly from one brake boss to the other, but it can't because the tire/wheel is in the way, so it must go around and the result is an arch.


Unless you were rocking one of these bad boys...

<img src = "http://4.bp.blogspot.com/_urSQl6wUA5g/S3qpl0pU3XI/AAAAAAAAH0U/EQXY4GCLigQ/s400/Hubless+Wheel+Yale+1.jpg">


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## unterhausen (Sep 28, 2008)

jtmartino said:


> Unless you were rocking one of these bad boys...


fails the kidney rule. I guess disc brakes are out?


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## JaquesN (Sep 14, 2009)

jtmartino said:


> I've seen it in person on a few of my own bikes - the seatstays themselves are pushed away from the rim when brakes are applied.


Not trying to beef with you and others in any way, but wouldn't a seat stay bridge have the same effect as the arch of a wishbone?


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## jtmartino (Jul 31, 2008)

unterhausen said:


> fails the kidney rule. I guess disc brakes are out?


No need for brakes on your fixie hubless bike 



JaquesN said:


> Not trying to beef with you and others in any way, but wouldn't a seat stay bridge have the same effect as the arch of a wishbone?


I assume so, yes. My comment was directed toward PVD's about the brake booster, not the merits of wishbone stays.


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## Eric Malcolm (Dec 18, 2011)

I have noted and followed this thread some time ago and wanted to raise a thought on this subject, but let it pass. Now that it has re-opened, I would like to say that I am wary of flippant comments that dismiss an idea without backing up with real facts.

If we are to understand the design, then compare tangible facts like deflection loads.
These are known as Moments of Inertia.
They can be looked at in a simple way as a value.

If I have a seat stay of 14 x .7mm the MoI = .002 x 2 stays = a value of .004
I look at using a mono tube of say 25.4 x .9mm @ MoI = .012 and use seatstays @ 16 x.7mm @ .002 x 2 stays and you have a stronger set-up.

Clearly, using a small Dia brake bridge will not compete with a folded around wishbone (being the closest effective point to the brake load).

I don't advocate for either design, but would prefer a good reason to be given as to which is better.

Eric


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## Francis Buxton (Apr 2, 2004)

Eric Malcolm said:


> I have noted and followed this thread some time ago and wanted to raise a thought on this subject, but let it pass. Now that it has re-opened, I would like to say that I am wary of flippant comments that dismiss an idea without backing up with real facts.
> 
> If we are to understand the design, then compare tangible facts like deflection loads.
> These are known as Moments of Inertia.
> ...


But you're kind of comparing apples to peaches here. On the "traditional" design, you're using 14mm x 0.7mm stays. On the wishbone design, you're using 16mm x 0.7mm and 25.4 x 0.9mm, which are both larger diameter tubes (one of which is also 0.2mm thicker wall). Just based on the material thicknesses/diameters, it "should" be stronger, but it's also heavier. For a true comparison, you would need at least the stays to be the same diameter/thickness.

You're also not looking at this (at least in my mind) from a structural standpoint. The traditional design is more of a true triangulated design, and the wishbone adds a weld joint and a separate tube in the upper portion, which is going to behave differently. From a braking force comparison standpoint, I can't see that there would be a tremendous amount of different between the two if there is a seatstay brace in there. That SS brace would be in largely the same position as the connection of the wishbone, and should provide similar "pulling" force to resist brake calipers on a rim attempting to push the stays out.


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## Eric Malcolm (Dec 18, 2011)

Francis

Thanks for your thoughts. My sizing was not meant to be comparitive, rather, intended as a sound technical basis for discussing using a form calculation as opposed to saying 'its rubbish' without qualifying why.

Personally, I have found V-brakes and cantilever brakes when used on the rear, both types will in real world use, have locked up the rear wheel well before the stays even begin to push out. So I'm inclined to think in terms of brake chatter (locked up rear wheel catching hard objects then soft) creates a bending moment, so structurally, the shorter the stay, and more solid connection above the rear tire is a less 'bendy' proposition.

I guess in my riding, I am a heavy front brake user, so I tend to have a very light load on the rear wheel under braking, so this will influence my personal view. I know other riders have a different style and catch tree roots and rocks while feathering the rear brake which is where I observe the 'chatter'. Simply pulling on the brake lever at standstill will push a stay outwards, but I don't use as much force when actually riding. Hence my comment to not having a preference. If you like a certain style, I don't believe mono vrs twin stays should be influenced by brake performance in the context of this discussion. The winds are blowing in the direction of Disc's on all forms of bikes making the seatstay style redundant.

Eric


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## wort (Jan 9, 2013)

smudge said:


> "figure out how you want to build a bicycle and then make up whatever technical B.S. you want to help you sell them"


I remember a guy at my Schwinn dealer years ago tell me that the "epicenter" (wishbone s-bend) seat stays on my Moab were designed to eliminate outward flex when the brake was applied. His explanation was that the tube was harder to bend back after it had been bent once. He even had a piece of welding rod that he bent and then gave to me and asked me to bend back.









While his explanation is pretty bogus (the metal gets work hardened, but that wouldn't affect the stiffness) the stays _are_ pretty stiff to brake forces (bowing outward), which I attribute to simple triangulation.

This 'feature' (the s-bend) has nothing to do with the mono-stay - it could easily be implemented on a bike with traditional seat stays by bending them in an S and then putting in a bridge, like this:

https://www.cxmagazine.com/wp-conte...-cyclocross-bike/kew7956_desalvo_nahbs_05.jpg

I do agree with PVD that wishbone and s-bend stays aren't as stiff laterally (during cornering), and probably make the bike less 'vertically compliant' as a similar bike with traditional (triangulated) seat stays.


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## Eric Malcolm (Dec 18, 2011)

I will add an interesting detail between design types as weight variations have been mentioned.

Using a weight calculator provided by Performance Metals - Australia, looking at a seat stay length of 500mm.

500 x 16 x 0.7mm x 2 stays = 262grams

Mono type: 340 x 16 x 0.7 x 2 stays = 178grs.
Plus 1 mono tube: 180 x 25.4 x 0.7mm = 76grs, Total = 254grams

Both have no bridge, not mitred or slotted for the drop-out. The mono is 20mm longer to give an attachment point for a bridge.

Not an issue as far as I can see.

Eric


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