# whats so bad about single pivot frames?



## AlexJK (May 2, 2009)

people say that they are flexy... how do they flex? which direction, whats it feel like?

i'm in the process of building a single pivot Freeride bike with a small, longer travel version of the honda unit pro-link or the standard pro-link.

the prototype is already mocked up and gets a proportinate 9 inches of travel! 
i'm also mounting the swingarm pivot around a beefed up BB shell (no need for any horst link sillyness! AND gives the ability to run single speed if desired!!)


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## yetibetty (Dec 24, 2007)

I thought that a single pivot had less flex due to less places to flex.

Just that the suspension feels less active as the wheel moves in an ark rather than the more up & down provided by variouse links, also the varouse link types can add leverage to the shock and make the suspension more active. Each extra link can add a touch of it's own flex though.

Having said that the more active the suspension is(more pivots)the more it will help provent the main structure from flexing as more shocks are absorbed.


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## pvd (Jan 4, 2006)

It has nothing to do with flex. Take a look at a Foes with the stabilizing link. No reason why that is any more flexy that a VPP or a Horst. I'm even sure it's stiffer.

http://www.foesracing.com/lineup.cfm?view=rs7

It's about wheelpath, the way the tension on the chain or force in the brakes effects the movement of the system. It can eat up a bit of energy and cause break jack.

Perfectly good for your first few FS bikes.


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## AlexJK (May 2, 2009)

pvd said:


> It has nothing to do with flex. Take a look at a Foes with the stabilizing link. No reason why that is any more flexy that a VPP or a Horst. I'm even sure it's stiffer.
> 
> https://www.foesracing.com/lineup.cfm?view=rs7
> 
> ...


well what do you think of this kind of link?
https://images.sportrider.com/bikes/2004/2004-honda-cb1000-upl.gif
that was the honda unit pro-link

https://www.hondanews.com/categories/1163/photos/14810
that was one version of the pro-link

https://www.motorcycle.com/gallery/gallery.php/d/12441-5/prolink_diagram.jpg
thats a compairison between the standard pro-link and the unit pro-link


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## AlexJK (May 2, 2009)

another thing, i'm torn between chromoly and aluminum... i was thinking of maybe using chromoly for the frame and aluminum for the swinger.

the frame is going to be comprised of a solid peice of oval tubing (braced of course)

i'm also wondering about how big of a head tube i can use, i want it to be pretty beefy.

i saw a carbon cannondale freeride lookin bike that had like a 3 inch head tube :idea: 

i don't think i want it that big though


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## pvd (Jan 4, 2006)

AlexJK said:


> well what do you think of this kind of link?


Those are all just simple swingarms. The linkage is only changing the wheel rate along the stroke, not the path. Honda developed the Unit Pro Link as a cost cutting design. There really isn't anything special about it unless you are looking to reduce manufacturing costs. Bicycles have very differerent needs when it comest to rear suspension under power. That is where the modified wheelpath designs come into play. Motoguzzi tried some parrallagram systems in the eighties. They gave up. It just turns into a huge problem with that much power going through the system. BMW has been doing the Paralever design for a while, but they are forced to (and own the patent) to reduce shaft drive climb.


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## pvd (Jan 4, 2006)

AlexJK said:


> the frame is going to be comprised of a solid peice of oval tubing (braced of course)
> 
> i'm also wondering about how big of a head tube i can use, i want it to be pretty beefy


Bigginer mistake #1: Fogetting that you are building a bicycle and not a motorcycle.

Keep it light or it will suck. Flex is way better than tank.


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## AlexJK (May 2, 2009)

i knew somone would say that! ha ha ha! it's actually really lightweight! the whole setup isn't the simplest but you'd be surprised at how lightweight it is! on a motorcycle the loads are much higher and the parts are made accordingly (my dirtbike has taken hits many times that of any MTB i will ever ride, some of over 10' high takeoff, over a 100' gap to flat)

the mtb parts will be smaller and lightened in various ways.

and even if it doesn't work (i don't expect it to the first time) i like to find ways to make it work. that is one of my greatest passions.

call me crazy but i think it's fun! :thumbsup:


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## AlexJK (May 2, 2009)

bah! gotta learn some way right?!

the pro link actually is really good at providing bottoming resistance, if it were just a cost cutting design then why have all of the japanese companies copied the pro-link design?

that and the fact that it's used almost exclusively in their race machines

anyway, help me understand brake jack!
i have a pretty good knowlege of suspension stuff but brake jack is one of those things that makes sense inn my brain but i can't really understand it...

i like to learn!


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## AlexJK (May 2, 2009)

pvd said:


> Bigginer mistake #1: Fogetting that you are building a bicycle and not a motorcycle.
> 
> Keep it light or it will suck. Flex is way better than tank.


oops  didn't read what you quoted me on!

it's not heavy at all! this tubing is plenty strong and is plenty lightweight!
i've used it many times for various uses like game hangers.

they also use it in aircraft, that has to account for somthing!


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## AlexJK (May 2, 2009)

how about a floating caliper with a pushrod connecting it to the frame?? thats used in the motorcycle world!


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## pvd (Jan 4, 2006)

AlexJK said:


> bah! gotta learn some way right?!
> 
> the pro link actually is really good at providing bottoming resistance, if it were just a cost cutting design then why have all of the japanese companies copied the pro-link design?
> 
> that and the fact that it's used almost exclusively in their race machines


1. Honda has a patent on the configuration.

2. Every bike is different just as their manufacturing process. I belive that without a complex swingarm design, the UPL wouldn't make any sense.

3. Any linkage system can produce an increasingly progressive rate. This is not exclusive to UPL. FYI, in the sportbike world, kit parts are used to remove most of progressivity from the rear. The consumer system is designed that way as a failsafe. On the track, you want it linear.



AlexJK said:


> anyway, help me understand brake jack!
> i have a pretty good knowlege of suspension stuff but brake jack is one of those things that makes sense inn my brain but i can't really understand it...


You are really going to have to buy at least 2 books.

* Tony Foale's "Motorcycle Handling and Chassis Design, The Art & Science" http://www.tonyfoale.com/book.htm

*John Bradley's "The Racing Motorcycle: A Technical Guide for Constructors, Volume 1" http://www.amazon.com/Racing-Motorcycle-Technical-Guide-Constructors/dp/0951292927

Those two books will get you started.


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## pvd (Jan 4, 2006)

AlexJK said:


> how about a floating caliper with a pushrod connecting it to the frame?? thats used in the motorcycle world!


Many bicycles use floating calipers, too. They are a good solution, but they add more weight, cost, and possiblity for problems.


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## pvd (Jan 4, 2006)

AlexJK said:


> they also use it in aircraft, that has to account for somthing!


I'd have to look at your design, but you need to remember that bikes have been evolving for about 150 years. The way they are put together has very good reasons. You want to go out on a limb, make sure that you know what side you are sawing.

Really, take a good look at an Intense M6 or a Foes DHS Mono to get a feel for the scale and state of the art in the area you are talkinga about. They both use different rear end designs, but they are similar in many ways. If you are going to deviate very far from those two designs, you should have some very good reasons for doing so. Not just hunches.


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## Monkeybike (Feb 25, 2008)

it is not about rigidity, wheel path or brake jack, it is about marketing.


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## becik (May 5, 2008)

Effectively single pivot, if not supported by another link (like foes) tend to be flexy.
The flex is induced by the swingarm itself, not the pivot.
In a design like vpp or fourbar you have more points of attachement therefore less possibility for swingarm to flex. 

I don't think it's a good idea to base your design on a motocross suspension.(beside the link system)
The forces are not de same (in size and position)
On a motoX the chain sprocket that deliver the power is small and allways as close as possible near the swing arm axle.

If you put your main pivot on the BB axle with 8"+ of travel you will have a lot bobing.
The tension on the chain, deliver via a relatively big chainring, when pedaling, will try to bring the rear weel up and fwd.

(my points of view)


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## popoff (Dec 4, 2007)

if you are building your front triangle from steel and swingarm from aluminum, here are a ew things to keep in mind. 

steel for the front triangle - you might find that by the time you add reinforcement needed for pivots/mounting points you could get pretty heavy. your unit pro link design may minimize hard points on the frame, so it could be made to work well. its a great material for a prototype as you can use straight gage steel or chromoly, its relatively easy to weld, cheap and forgiving. once you get your suspension system worked out you can go back and concentrate on weight reduction. 

aluminum for the swingarm - easy to machine, reasonable material cost, welding its more difficult (but i don't know your skill level, its something you can work up to if you have some time). one thing to consider is heat treatment its pretty expensive and time consuming with a big chance of warping of your parts. you will want to overbuild on the prototype if you want to skip heat treatment or skip solution and age it in your kitchen oven. 

one other thing i see with the prolink unit layout, it looks like it will eat up some space between seatpost and rear tire forcing you into a longer chainstay/swingarm, and it will put some massive force on the 2 mounting points, so you need to keep that in mind as you design the frame. also don't forget about front derailleur placement and clearance. there is a new shimano direct mount ft derailleur that might be easier to fit. 

i would say approach it one step at a time, start with a buildable design to get something on the ground to start with, then work toward refinement of performance and weight. it will be way more motivating to have something to ride so you can figure out where to go from there compared with a never ending design which tries to perfect everything in one pass. 
tailor the build to your skills, use thicker wall tubing if you are still ramping up your welding skills, use joints that are within the skills and tools you have to fabricate. its better to have a simple solid prototype than one that attempts high end fabircation unless you are already there. 

good luck
Mike


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## AlexJK (May 2, 2009)

it's not going to have a front mech, i'm gonna hook up either a b-boxx or a hammerschmidt.

the seat tube is only gonna be 4-5 inches long, using a scratch made tube to connect it to the frame, which will be also be braced.

i'll try to get a scan of it


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## Peter E (Feb 16, 2004)

Horst link, VPP, DW link etc are NOT better than single pivots when it comes to pealing efficiency. That is all marketing BS. Correctly designed, four bar linkage bikes (horst, vpp, dw are all different versions of four bar linkages) can be more active when braking/less sensitive to brake jack. But when it comes to pedaling, a single pivot can be just as good as all the others. All that talking about special axle paths is just pure BS. 
As DVD pointed out single pivots can me mighty stiff, if they are well designed like the Foes. There are four bar designs out there that are way flexier than some single pivots.
Braking is their main problem. Some people find it bothersome, others don’t notice. Sure it can be cured with a floating brake but that’s rarely a nice looking fix.


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## pvd (Jan 4, 2006)

Peter E said:


> Horst link, VPP, DW link etc are NOT better than single pivots when it comes to pealing efficiency. That is all marketing BS.


That is only true for a case where the single pivot has been designed to be used in a specific gear. Once you deviate from that gear, things will get much worse. The wheelpath designs have an advantage here. The s-path bikes drive the wheel to a specific postition of the stroke while the chain is under tension, but this force is easyly overcome by bump input. It really works well.

From my experience, I'd take a VPP over a Horst, and a Horst over a single pivot.


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## Peter E (Feb 16, 2004)

think you have been reading too much on the manufactures web sites. as I said its all BS.

the S-shaped paths you are talking about does not exist in real life. Only in marketing. In real life 99% of all linkage bikes have axle paths that are extremely close to a perfect arc. The difference between the axle path and a perfect arc is almost always less than 0.02", often less than 0.01". There is no way anyone could feel a difference between two bikes where the axle path differs 0.01"


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## eMcK (Aug 22, 2007)

I won't claim to be an expert on suspension design, I do ride a lot of bikes, and can say unequivocally many work as advertised. 

This isn't to say a well designed single pivot bike can;t work very, very well. But the newer multi-link bikes do a very good job of keeping bob and brake jack to minimum while remaining active to bumps.

Now whether or not this is due to an S shaped axle path, I do not know. I do know it isn't the compression damping. 

Is your claim that no one can feel the minute difference in axle path based on saddle time or computer time?


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## pvd (Jan 4, 2006)

Peter E said:


> as I said its all BS.


You can say anything you like. I've been riding for a very long time on many types of designs. I can say from personal experience that VPP puts power to the ground way better than Horst and way way better than Single Pivot.

Why don't you prove your claims with some diagrams?


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## jay_ntwr (Feb 15, 2008)

Peter E said:


> think you have been reading too much on the manufactures web sites. as I said its all BS.
> 
> the S-shaped paths you are talking about does not exist in real life. Only in marketing. In real life 99% of all linkage bikes have axle paths that are extremely close to a perfect arc. The difference between the axle path and a perfect arc is almost always less than 0.02", often less than 0.01". There is no way anyone could feel a difference between two bikes where the axle path differs 0.01"


Yeah, I'm with Peter, you're going to need to provide some sort of documentation to back this up (maybe if you do that, he'll tell us why 10spd chains are better).

Firstly, not all four bar linkages are the same. You can have a rocker-rocker, a crank-rocker, drag link, and that's just off the top of my head. It's been 10 years since I was in my kinematics course.

Secondly, toggle points in a 4 bar are what make the "new" suspension designs work. It still blows my mind that they can get patents on a linkage, so I'll give you that. But somehow they've managed to do it. Path is not something to worry about as much as the toggle points in the linkage. Specifically a toggle point prevents movement in the linkage. Think of a pair of scissors. They work really well with your fingers in the ends and putting force into the opening and closing direction. But if you were to push on them toward the pivot, then they resist opening and closing. There is a lot of design that goes into suspension systems that try to counter breaking, bob, pedal forces by inserting well thought toggle points in the linkage.

Now I haven't ever modeled the coupler curve of any of these linkages but that isn't as important as resisting the other forces. The coupler curve or "arc" as you call it is going to look how it looks and that's irrelevant with respect to how a bike is actually going to ride.

There are trade offs in all the designs. Some resist pedal forces better than others, some bob less, but they each approach all the same problems and try to limit the negative affects.

Marketing doesn't control Kinematic Design, Physics do. And I will say that Kinematic Design isn't easy--or it didn't use to be so easy. Now there are some very powerful software programs that help analyze linkages, but they didn't exist 10 years ago. Doing it all by hand was brutal. Doing it with math (yes, you can do it all in equation form if you've got a great math background and understanding) is even more brutal.


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## Peter E (Feb 16, 2004)

What I claim is that almost all linkage bikes out there have axle paths that are very arc like, paths that could be copied to 99.9% of a single pivot. I don't know how many diagrams I have made throughout the years but I have done quite a few.

Here is one of the Intense 6.6. As you can see there is no S-shaped axle path









1. Using a CAD program I have plotted the position of the rear axle in 0, 25, 50, 75 and 100% of travel.

2. Using three axle positions (the 0, 50, 100%) I have created an arc (blue line) In the diagram its not possible to see the axle path of the 6.6 since it does not differ enough to the arc). The cross hair shows the location of the centre of that arc.

If one would build a single pivot bike with the same geometry as the 6.6 and place the pivot at the cross hair, the two bikes will have extremely similar axle paths. In the 0, 50 and 100% travel positions the rear axle paths of the bikes will match perfectly. In between these positions they will differ. How much depends on the design and how much travel the bike has. The more travel the more they will differ.

In the case of the 6.6 the max deviation between the axle path and arc is about 0.02", located at the 25 and 75% travel positions. Most linkage bikes have axle paths that differ less than the VPP designs. Usually less than 0.01"

Lets say you build that single pivot copy of the 6.6. When you pedal it there will be a difference in chain growth/pedal feedback of 0.02" compared to the original 6.6. That's nothing! No way could anyone feel that.

Braking is a completely different thing, then the linkage bikes, if correctly designed will out perform the single pivots.

If you want to understand how different suspensions design works, start with some cardboard and pins. You will learn much more than from a book about motorcycle suspension.


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## jay_ntwr (Feb 15, 2008)

Peter E said:


> What I claim is that almost all linkage bikes out there have axle paths that are very arc like, paths that could be copied to 99.9% of a single pivot.
> 
> You will learn much more than from a book about motorcycle suspension.


Great, we agree 100% then. You can copy the axle path no problem. But that axle path has absolutely nothing to do with how the linkage performs under braking, power, or when the rider is out of the saddle. That's where the single pivot fails.

Sure, it works great on a motorcycle where weight isn't as big of an issue %age wise in terms of total weight of the system and power is essentially unlimited.

Plotting curve, don't need cardboard, I can do it in 3D and actually run analysis on MSC's Nastran and come up with not only the linkage but the forces, velocities, an stresses in the linkage. But there is more to Kinematics than driving a CAD system. It's what separates a Mechanical Engineer from a Mechanical Designer, or one of the biggest things.

So yes, you've got the path at the wheel but again, it means nothing in terms of how the bike is going to work.


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## Peter E (Feb 16, 2004)

jay_ntwr said:


> I can do it in 3D and actually run analysis on MSC's Nastran and come up with not only the linkage but the forces, velocities, an stresses in the linkage.


why don't you do that. Go ahead with lets say the 6.6. Prove that when it comes to pedal performance that it will differ. I seriously doubt that you have actually given this problem enough thought.


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## pvd (Jan 4, 2006)

Peter E said:


> Here is one of the Intense 6.6. As you can see there is no S-shaped axle path.


Good work. I'm a bit busy during the day today, but I am going to take some actual measurements from my M6 and plot them out in solidworks. If I get the same result, I'll give it up to you. I have some old models somewhere where I studied this myself. I'll look for them again as well.

Thanks for coming through.


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## Peter E (Feb 16, 2004)

Have not plotted the M6 but I did plot the V10 when it was new. It did definitely not have a arc like axle path. Thats why I wrote 99%. The longer travel VPP's belong to that 1% group. Didn't you get a Tracer for your girl friend ? If possible plot that one too.

the original v10
https://www.mundobiker.es/images/stories/pa/chapter4/image030.png

looking forward seeings your diagrams


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## jay_ntwr (Feb 15, 2008)

Peter E said:


> why don't you do that. Go ahead with lets say the 6.6. Prove that when it comes to pedal performance that it will differ. I seriously doubt that you have actually given this problem enough thought.


I don't see how this would solve/prove anything (other than wasting a day or two of my time). You're still arguing that wheel path is the only thing that matters. I'm arguing it has very little to do with the way the suspension design will work. Those are fundamental barriers in moving the discussion forward.


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## Peter E (Feb 16, 2004)

just so that I know I have understood you correctly.

Two bikes, one single pivot, one four bar. 

More or less identical axle paths, same shock, shock rate, rate of the linkage (or at least very close), centre of gravity, rider height etc. 

You are saying that the linkage bike can be designed to perform better when pedalling. Right ?


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## jay_ntwr (Feb 15, 2008)

Peter E said:


> just so that I know I have understood you correctly.
> 
> Two bikes, one single pivot, one four bar.
> 
> ...


It's hard to say that the shock, shock rate, and rate of linkage (whatever that means) would be the same without going through a fairly detailed analysis. This is like assuming that one Monroe strut could be used on any passenger car and it would work properly. That seems like a invalid assumption.


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## herbn (Sep 17, 2005)

I don't trust diagrams like that, to neat But i visualize that the two corners of the rear triangle that are moving on links of different lengths there will be a ratio between the speed the links move,and by looking at the angle of the links you can visualize how they are gonna influence the wheel path.....I just looked up at your very "neat" drawing,looks like you did some impossible things with the seatstay lines to make a perfect arc happen.


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## pvd (Jan 4, 2006)

Peter E said:


> Didn't you get a Tracer for your girl friend ? If possible plot that one too.


Actually, just friend now, but I'll do the other bikes when I get around to it.


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## popoff (Dec 4, 2007)

its interesting to see other people sketching up axle paths too. here are my crude versions of the dw sultan and the rip9:



the sultan effective pivot ends up about 3.1" above and just slightly forward of the bb. this is pretty close to the pivot location on old cannondale super v900. a bike with a single pivot located where the sultan's is would be a bear to mount a front derailleur on, cannondale's approach was pretty good.



the rip actually has a linkage that is still very close to an arc, but with a very rearward pivot, about 7.3" back and 2.25" above the bb.

i think the advantage of 4bar link bikes is packaging and eliminating the need for a floating brake caliper mount, and in the case of the rip, get a pivot point way outside the main triangle. i also completely agree with Peter E about axle path's influence on pedaling feel/feedback/etc. for pedaling, since the rear wheel is on a bearing (not transferring moment at the hub to the frame) axle path is axle path. suspension rate also obviously has a huge effect, but there is so much flexibility with linkage design that you can get almost any rate you want.

another item to note on the S path bikes, some of them are pretty much an arc around the static sag point, then they curl back deep in the travel. that arc around static sag is what will be noticed most of the time while pedaling, maybe some people are animals and can pedal through while stuffed 80-90% or their travel, but i bet most people are not spinning that far into the travel.

i'm curious to know if anyone is riding a single pivot bike (swing arm with pivot near rear axle, like a kona) with v-brakes and a well set up shock and could comment on how the rear suspension feels while braking, it should be pretty active since the brake is transferring moment to the seatstay, not the chain stay. its the same idea as the cs/ss pivot concentric with the rear axle that dw designed and trek/gf is using on some of their bikes.

Mike


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## Guest (Jul 16, 2009)

*Go for it!*

Alex, I like the way you think, go for it! Weather it sucks or is the coolest thing ever you will learn something and have fun with it. Pay no mind to all the "suspension diagrams" and nay sayers. just think what the world would be like if Christopher Columbus had listened to all the folks that no doubt whipped out maps and made super cool diagrams of why his journey to the new wold would not work. I cant tell you how many rides have ben ruined by heated discussions of who's bike has better wheel travel or better geometry or some kind of techno garbage than the rest of the group:madman: . Its funny how that conversation usually takes place at the back of the pack.... (usaly behind a bunch of hardtails :eekster: )...hmmmm weird. Thanks for keeping this discussion where it belongs, here. Alex Go for it!


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## AlexJK (May 2, 2009)

Peter E said:


> If you want to understand how different suspensions design works, start with some cardboard and pins. You will learn much more than from a book about motorcycle suspension.


that is exactly what i've been doing! i've learned alot from it!


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## eMcK (Aug 22, 2007)

I seemed to recall reading something from Santa Cruz saying something along the lines of "sorry about that S shaped stuff, turns out it doesn't matter". I was right:

http://www.santacruzmtb.com/news/index.php?JoesCorner=1&display=3

A short quote: 


> Here's something that nobody wants to hear: Axle path doesn't matter for bicycle suspension. At least, it doesn't matter nearly as much as some people say. It's true. Axles move up and down, and everyone can imagine that they follow a certain path, so it's an appealing thing to think about. But unfortunately, describing an axle path as "vertical", the classic "near-vertical", "s-shaped", or "rearward", is an over-simplification of the suspension system


Interesting reading in there, also some words on instant center and shock rates.


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## pvd (Jan 4, 2006)

jimfab said:


> Pay no mind to all the "suspension diagrams" and nay sayers.


Nobody here has been trying to discourage him from building a single pivot bike. The discussion has digressed to the finer points of linkage and wheelpath configurations.


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## pvd (Jan 4, 2006)

I'm pretty busy right now. I'm going to return to this subject when I get back from my Whistler vacation (leaving in a week). I've also just gotten a HAAS MiniMill up and running at work and along with the small lazer cutter, I've got a lot going on. Learning new CAM sucks.

I quickly modeled up a new Uzzi VP frame. I'm going to go ahead and conceed the point on axle path. It is very close to a "virtual" simple pivot. I'd like to get down to more on this issue though as I do notice differnces from one design to another. Explainations must exist. Wether it's chain growth or wheel rate or pivot location or damping.

Ok, back to CAM and fixturing...


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## Jerk_Chicken (Oct 13, 2005)

You guys need to read this thread:

http://forums.mtbr.com/showthread.php?p=5899532#post5899532


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## Thylacine (Feb 29, 2004)

I'm guessing just for fun, JC goes into churches in the middle of a sermon and screams "GOD DOES NOT EXIST!".


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## Jerk_Chicken (Oct 13, 2005)

No, I play the first Black Sabbath album as I drive by them. Big difference.


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## Thylacine (Feb 29, 2004)

Well I guess the loons probably have a whole heap of guns back at the compound so that's probably a wise move.


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## nogod (May 30, 2009)

pvd said:


> I'd have to look at your design, but you need to remember that bikes have been evolving for about 150 years. The way they are put together has very good reasons. You want to go out on a limb, make sure that you know what side you are sawing.
> 
> Really, take a good look at an Intense M6 or a Foes DHS Mono to get a feel for the scale and state of the art in the area you are talkinga about. They both use different rear end designs, but they are similar in many ways. If you are going to deviate very far from those two designs, you should have some very good reasons for doing so. Not just hunches.


yea a 150 year rut. im not saying i have the answers or the next great design. but just because someone has been doing something the same for a long period of time doesnt mean its the best idea. after all the world is not flat.


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## 18bikes (Jan 15, 2007)

i think some people on this thread may enjoy looking at a program called linkage, it'll save you doing all the drawings yourself, and you can play with it endlessly if you buy it, which i seem to remember wasn't big money at all. if you don't buy it you can still modify the designs that are already in it in the free version

matt


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## nogod (May 30, 2009)

ok i love this thread! 

heres what im thinking...

i understand the concept of the virtual pivots being more important then axle path. and the axle path is just a result of linkages.
but with that said. if one knew what effects the actual different axle path's have on peddling and braking. then that path could be more tailored for the desired use of the bike.

after alll if you design the entire swing arm for what you want. trying to eliminate the undesired geometry, or at least compromise the good and bad. then we might move forward instead of side stepping like whats been going on in FS technology.


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## AlexJK (May 2, 2009)

18bikes said:


> i think some people on this thread may enjoy looking at a program called linkage, it'll save you doing all the drawings yourself, and you can play with it endlessly if you buy it, which i seem to remember wasn't big money at all. if you don't buy it you can still modify the designs that are already in it in the free version
> 
> matt


i can't find it, got a link?


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## brant (Jan 6, 2004)

AlexJK said:


> i can't find it, got a link?


http://www.bikechecker.com/


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## smilinsteve (Jul 21, 2009)

This is a great thread. I love reading the thoughts of the suspension brainiacs on all the theory of what should work and why. I'll keep it simple for laymen and answer, IMO, the OP's question:



> whats so bad about single pivot frames?


Answer: Nothing. 
I have a Santa Cruz superlight single pivot, and a Jamis 4 bar, and have rented lots of different four bar type bikes just to try them out. 
All bikes feel different, which is not the same as saying one is better than the other. I like how my sp bike feels, a lot. Compared to some of the others I have tried, I will say that braking stiffens the suspension. It doesn't negate the suspension, just makes it a little rougher on technical downhills than others, which is something that doesn't bother me at all. As far as climbing, I think it works as good as most any other bike I have tried. Very responsive, snappy, stiff, are some words I would use. Some bikes that claim to keep the wheel on the ground better during climbing seem a bit mushy to me, so I am not sure they are more efficient in the long run. 
The differences are small anyway. there are grandmas out there that can zoom past me on rigid single speeds, so I think that for me, and lots of other people like me, these technical arguments are interesting, but not important in defining the quality of your riding experience.


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## pvd (Jan 4, 2006)

Steve, I don't know what they did in the past, but all of the 2009 Jamis FS bikes are single pivots. You may want to take a second look at what you have.

http://www.jamisbikes.com/usa/tech/images/09_xam_techsheet.pdf


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## LWright (Jan 29, 2006)

I would think single pivot would work best for lesser travel. at 9 inches the rear wheel will be under the top tube! So I my be exaggerating, but you get the point.


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## smilinsteve (Jul 21, 2009)

pvd said:


> Steve, I don't know what they did in the past, but all of the 2009 Jamis FS bikes are single pivots. You may want to take a second look at what you have.
> 
> http://www.jamisbikes.com/usa/tech/images/09_xam_techsheet.pdf


You are right it's not really a four bar, but different from my superlight, which is a true single pivot, because the Jamis has a pivot near the dropout on the seatstay, and the swing arm connects to a link, rather than directly to the shock. Even though I have seen this design referred to as a type of single pivot, it obviously has multiple pivots, and I think it is more often referred to as a "swing link" type of suspension (like the rocky mountain element). 
Thanks for catching that. 
Regardless of what you call it, it rides different than my superlight, which rides different than my hardtail. You could say that one might be better under certain conditions, but for overall riding experience, I prefer to think of them as different, rather than ranking them from best to worse.


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## pvd (Jan 4, 2006)

The bike is a pure single pivot, just like the superlight. The pivot location may be slightly different and the wheel rate as well, but the two bikes are identical with regard to their definition. Single pivot. Something about the pivot location or wheel rate is what you must be feeling.


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## smilinsteve (Jul 21, 2009)

pvd said:


> The bike is a pure single pivot, just like the superlight. The pivot location may be slightly different and the wheel rate as well, but the two bikes are identical with regard to their definition. Single pivot. Something about the pivot location or wheel rate is what you must be feeling.


No, the superlight does not have a pivot on the seatstay, and does not have a link (which has a pivot connecting the link to the frame and a pivot connecting the link to the swing arm.) So, how can you say it is "pure single pivot" or "just like the superlight."
Clearly, not.

How about the Chumba, what would you call it? 
http://www.chumbaracing.com/vf2.shtml
I would call it the same basic suspension type as the Jamis, with the exception of a horst link pivot instead of a seatstay pivot. 
Mountain bike action calls it a "Horst-Link rear suspension with a swing-link-guided mac
strut".
http://www.chumbaracing.com/images/mba_0607_chumba_xcl_review.pdf
I know the Chumba horst link is different than a seatstay link, and people quibble over that difference, but that is minor compared to the difference between the Jamis and the Superlight!

Jamis calls it their "mp3" multilink design.
http://www.jamisbikes.com/usa/thebikes/fullsuspension/index.html

I don't mean to mince words, but if you look at the Chumba, the Rocky Mountain element, the Jamis dakar, and the Superlight, you can't say they are the same. A link and pivot on the seat or chain stay can not be disregarded. Like you said, the link effects the spring rate. It also adds to lateral stability. The pivot on the seatsay affects suspension action during braking. So, they are different!

There are sub groups and overlaps between the defined suspension types. I know the axle path is defined solely by the chainstay arc for both bikes, but there is more to a suspension than that. That's why there are terms like macpherson strut, swing link etc, to define these designs.


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## shirk (Mar 24, 2004)

smilinsteve said:


> stuff


Singlepivot is the correct term for any suspension design that does not have a pivot between the rear axle and main frame pivot. These is nothing to affect the axle path on singlepivot bikes other than the placement of that main frame pivot.

This has been argued to death on every bike forum. Some people get some just count pivots and not actually understand the affects of placement.


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## pvd (Jan 4, 2006)

smilinsteve said:


> No, the superlight....


The Chumba (that you linked to) is a Horst (FSR) link. All of the Jamis stuff are single pivots. The Santa Cruz super light is a single pivot as well.

This is simple stuff once you understand the basics of suspension configurations.


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## smilinsteve (Jul 21, 2009)

Ok, call it a single pivot because there is no pivot between the rear axle and the main pivot. According to that definition, the Kona dawg is also a single pivot, even though Kona calls it a walking beam four bar. (Some call it faux bar, like Turner TNT). 
http://www.konaworld.com/bike.cfm?content=dawg
The distinctions between the designs is interesting to me, and I appreciate your input, as I am sure you are more educated about it than I am. 
There are lots of subcategories under that broad classification of bikes that have no pivot between the axle and main pivot.The Jamis is way different than the superlight, in design, and in ride. To describe that difference, it would be useful to use more illustrative terms, like "swing link guided mac strut", etc. 
My point of bringing up the Jamis is because it is different than the superlight, no matter what you call it. 
You could call the Rocky Mountain element, the Jamis Dakar, the Turner TNT, the Chumba, the superlight, and the Kona all the same suspension design but they are not, even though they might fit the broad description of single pivot as it is defined here.


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## pvd (Jan 4, 2006)

smilinsteve said:


> ..even though Kona calls it a walking beam four bar...


You seem fixated on what the marketing and sales departments name things. You really have to stop paying any attention to add copy and hype. None of it means anything.


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## smilinsteve (Jul 21, 2009)

pvd said:


> You seem fixated on what the marketing and sales departments name things. You really have to stop paying any attention to add copy and hype. None of it means anything.


I understand what you are saying, but I'm saying that "single pivot" doesn't mean anything either, if bikes that are so different can be labeled the same. 
And the common names like faux bar, walking arm, mac strut, swing link, etc, actually describe the design, and those designs do perform differently, so I don't think you can say its just marketing hype that doesn't mean anything.

But yeah, they are all single pivots if that means no pivot between rear axle and main pivot, and I didn't understand that before, but I do now, so thanks for the discussion.


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## esilvassy (Jul 25, 2006)

Trying to make it clear the faux bar bikes are single pivots because the wheel path pivots around the one pivot near the bottom bracket (that location is a generalization, also I will refer to this as the main pivot)
They are more complex than a more plain single pivot like the style used on the superlight, but in the end the wheel path is determined just by the main pivot.
The seatstay pivots and the swing link control the rate that the shock is driven (more so the swing link), so there are more options available to the designer when these are in play.

Other suspension designs have a pivot in between the rear axle and the main pivot, with this various wheel paths can be obtained. Either way companies will tweak designs slightly and place different names on them for marketing and patent reasons, but there are still general categories that designs fit into. There is a good article in an issue of dirt rag from a few years back that goes over the general designs. They also have broad generalizations about pros and cons of each type.

Also saying all of that there are surely bikes with all types of designs that ride well, its up to you to figure out what works for you.

feel free to correct me but this is the way i understand the differences...


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## scottzg (Sep 27, 2006)

yo steve-

Riding a frame really doesn't tell you much, unfortunately. Sure, you can assess the complete unit- 'this thing climbs best standing, and it loves to jump' 'this suspension knows exactly what a bump is' but you can't isolate one design element and attribute a handling characteristic to it.

You're doing the biggest, most common thing- 'this suspension design is visually similar to this other one, ergo they have the same attributes...' and it's way wrong. Not only can two executions of the same suspension design handle VASTLY differently when attached to the same bike, but how the rest of the design- front triangle geo, stem, etc will really alter the bike's personality. What type of suspension design is implemented is only one (small) piece of the pie.

In general, this forum has all the people that _really_ know what they're talking about... which is why i mostly lurk, even if i technically might qualify as a 'framebuilder.'

Kona calls it a whateverthe****youtypedout because the mtb media has blacklisted single pivots.


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## frascati (Sep 23, 2009)

A very valid point. None of that ad copy and hype amounts to anything.


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