The suspension linkage thread!

[nouseforaname]

The Konas work (the suspension performs like...) like a single pivot but ARE a 4 bar. This is how Norcos engineer characterises it.
4 pieces which transmit movement = 4 bar. 4 bar is not a bike term. Specialized does not own the 4 bar patent, they own the horst link patent which refers to a pivot on the chainstay - not how many "bars the suspnsion system has. For an example of this see the early AMP frames, or the cheap specialized Grond Control FSRs.
Having recently started to ride a non Horst bike after 3 solid years of riding only Horst, i can honestly say that there are many other factors which affect the ride a whole lot more than where that pivot is. How high the forward pivot is HUGE compared to that area....
Usually its only bike shop employees who get hung up on the 4 bar/faux bar/single pivot debate. But i'm not surprised to see a potential "reference" thread turn into a debate full of misunderstandings and misreferences.

Edit - i just watched the Kona video and found it interesting how even "dr Dew" mixes up brake Jack with brake Squat. Intentional?

[xy9ine]

hope this doesn't turn into a semantics aguement, but 4-bar typically refers to a system in which the two bars (conected to a third bar to which the axle is affixed) define the wheelpath (unlike the kona). automotive references i've seen follow this logic as well - here's an example (the axle mounts to the perch in front of the shocks); axle path is defined by the two parallel bars:



maybe some suspension guys use the terminology differently; this is the most frequently used interpretation i've seen used among bike gurus.

again, semantics...

[ERregular]

As for the Sinister, I'm not an engineer, nor do I totally understand how it works. I have spoken to its designer and builder (FTW) who described it as a 5-bar (of course, this still means next to nothing to me). I've also had the good fortune of test riding one of the prototypes and it is pretty damn amazing. The best way I can describe it is that the rear wheel has an area of movement rather than a set path, since the path actually taken depends almost entirely on the hit taken. It is a very different feel than either my own single pivot, or any other 4-bar/faux-bar design I have ever ridden.

[big ben]

Originally Posted by ERregular

As for the Sinister, I'm not an engineer, nor do I totally understand how it works. I have spoken to its designer and builder (FTW) who described it as a 5-bar (of course, this still means next to nothing to me). I've also had the good fortune of test riding one of the prototypes and it is pretty damn amazing. The best way I can describe it is that the rear wheel has an area of movement rather than a set path, since the path actually taken depends almost entirely on the hit taken. It is a very different feel than either my own single pivot, or any other 4-bar/faux-bar design I have ever ridden.

sounds like it'll be an interesting bike to check out once it hits the market!

[Wayne P]

Originally Posted by nouseforaname

The Konas work (the suspension performs like...) like a single pivot but ARE a 4 bar. This is how Norcos engineer characterises it.
4 pieces which transmit movement = 4 bar. 4 bar is not a bike term. Specialized does not own the 4 bar patent, they own the horst link patent which refers to a pivot on the chainstay - not how many "bars the suspnsion system has. For an example of this see the early AMP frames, or the cheap specialized Grond Control FSRs.
Having recently started to ride a non Horst bike after 3 solid years of riding only Horst, i can honestly say that there are many other factors which affect the ride a whole lot more than where that pivot is. How high the forward pivot is HUGE compared to that area....
Usually its only bike shop employees who get hung up on the 4 bar/faux bar/single pivot debate. But i'm not surprised to see a potential "reference" thread turn into a debate full of misunderstandings and misreferences.

Edit - i just watched the Kona video and found it interesting how even "dr Dew" mixes up brake Jack with brake Squat. Intentional?

Thank you fer bein' all smart and stuff.

[Timmigrant]

Originally Posted by nouseforaname

The Konas work (the suspension performs like...) like a single pivot but ARE a 4 bar. This is how Norcos engineer characterises it.
4 pieces which transmit movement = 4 bar. 4 bar is not a bike term. Specialized does not own the 4 bar patent, they own the horst link patent which refers to a pivot on the chainstay - not how many "bars the suspnsion system has. For an example of this see the early AMP frames, or the cheap specialized Grond Control FSRs.
Having recently started to ride a non Horst bike after 3 solid years of riding only Horst, i can honestly say that there are many other factors which affect the ride a whole lot more than where that pivot is. How high the forward pivot is HUGE compared to that area....
Usually its only bike shop employees who get hung up on the 4 bar/faux bar/single pivot debate. But i'm not surprised to see a potential "reference" thread turn into a debate full of misunderstandings and misreferences.

Edit - i just watched the Kona video and found it interesting how even "dr Dew" mixes up brake Jack with brake Squat. Intentional?

Ya see the reason I would consider a Kona frame as a single pivot is because "single pivot" describes the rear wheel axle path. Bottom line if you remove all the linkage bits and the shock you have a pure and simple single pivot, with both the brake and the axle attached to the chain stay. The rest are just a linkage mechanism for actuating the shock. Much like a Rocky RMX / Giant Team DH type frame design, which we would all agree are single pviot designs, with a linkage actuated shock. On all 4-bar bikes (VPP, Maestro, DW, FSR, Lawwill etc) all 4-bars are used for describing the rear wheel axle path.

[ESHER SHORE]

Kona and Banshee's "Faux-Bar" is another name for "Rocker-Activated Single Pivot"

having a rocker allows fine tuning of the shock leverage ratio, and takes away side loading from the shock's bushings, improving the durability of the shock

I can feel some brake stiffening on my Chaparral but it doesn't affect my riding as i try not to use the brakes for extended periods in the rough or going through a corner

a bid advantage of the Banshee faux-bar i have found (having owned Specialized FSR and Devinci Horst pivot 4-bars) is that the faux-bar seems alot firmer under power, and does not have the pedal bounce i've always found on FSRs / Horst 4-Bars

this really helps going up hills, or accelerating out of a corner

[yoonior]

Originally Posted by ESHER SHORE

this really helps going up hills, or accelerating out of a corner

This is funny, I tend to think it's just the opposite. Have owned FSR bikes and ridden lots of Konas, I would say FSR is very efficient when pedalling (uphills/dwonhills) and Konas were much worse climbers.

[builttoride]

Originally Posted by yoonior

This is funny, I tend to think it's just the opposite. Have owned FSR bikes and ridden lots of Konas, I would say FSR is very efficient when pedalling (uphills/dwonhills) and Konas were much worse climbers.

first of all in terms of performance faux bars cannot be compaired to each other, some are far superior to others. Also a lot of it also depends on the rear shock setup.

[Sublime]

This has been talked to many times on this board, check out the link here for more information: http://bb.nsmb.com/showthread.php?t=51992&page=4


However, the best written description that I can find is from Knolly, and here are the goods...


Currently, the majority of the market is devided into a few major suspension designs:

Single pivot designs: means that the rear wheel's path is constrained to a circular arc. There are three main types:
1) low pivot - like the Kona Stinky, RM RMX, Banshee scream, etc...
2) forward pivot: SC Bullit, Cannondale Gemini, Orange Patriot
3) high pivot: Balfa BB7
Additionally, Single pivot bikes often include linkage actuated shocks (like the Kona and RM models) and may have floating brakes (Cannondale and Foes)

Four Bar linkage designs: These designs typically have the rear wheel on a linkage element that is not directly coupled to the frame. For this discusion, this will mean typical four bar bikes like those from Specialized, Titus, and Norco.
These designs follow some well establihsed guidelines and tend not to vere too much from the beaten path. However, there are exceptions: for example the Demo series (chainstay mounted shock) and of course Knolly's V-tach with out patent pending "Four by 4 Linkage"


VPP free designs: invented by Outland and currently used by SC / Intense. While technically four bar linkage bikes, they use a reversing "instant center" four bar geometry that creats axle paths and suspension feel that are substantially different that traditional four bar designs.

Parallel linkage designs: originally prominent in Karpiel bikes and advanced and specialized by companies like Canfield Brothers (great guys BTW), Dave Weagle (DW link: Ironhorse - another very cool guy) and now Giant with their Maestro line, these bikes offer another set of suspension performance characteristics each tweaked to the designers requirements.

Each of these designs have advantages and compromises - some subtle and some quite severe - depending upon your preferences. Here's a brief run down - and by no means a complete description of each types performance characteristics. Good engineering, a solid understanding of the products intended application, and a priority assessment of design criteria (i.e. what to include and what to sacrifice) are all necessary to achieve a superb product.

Typically, there are three main things that most people look at when comparing suspension designs (and lots of smaller things later on):

Pedal Bob: how much the suspension moves when pedalling - the worst situation usually exhibited when cranking out of the saddle. Pedal bob is typically cause by two factors: 1) tension on the chain which is not perpendicular to rear wheel movment causes a vector force to compress/extend the rear shock/suspension; 2) the change in center of mass of the bike/ride combination which causes suspension to compress (i.e. stand on your bike without pedalling but bounce up and down and you're going to compress the suspension).

Pedal feedback: This is caused when chain length changes. Designs which have a lot of change in chain length canl exhibit the worst feedback (there are exceptions - mainly high single pivot bikes with idler cogs). This is due to the fact that the rear cassette only rotates one way: if the chain length grows and the cassette can not allow the chain to slacken (i.e. take slack chain from below the cassette), it will have to rotate the cranks (typically backwards) to compensate for the chainlength growth.

Brake interaction: Brake jack is when the suspension extends and causes the head angle to steepen, the back of the bike to rise and generally wants to throw you over the bars. Brake jack is always considered a bad thing. Brake squat is when the suspension compresses under braking forces. It effectively pre-loads the rear shock, making it more difficult for the suspension to soak up bumps. This makes the suspension feel more harsh and causes the tire to "skip" across the terrain, reducing traction. However, brake squat also causes the back of the bike to be lower, so can help to offset fork dive and can help to balance the bike in steep situations, so it's not all bad. Some people (like Brake therapy for example) tout that a full active brake is the best situation for performance, while others tote that a small amount of brake squat can help in steep riding situations because it helps to counter-act fork dive.

Single pivot bikes:
Low pivot designs can have fairly high lateral rigidity, especially if enhanced by a secondary ancoring point (Foes, Yeti ASX). The low pivot design exibits only a small amount of chain length growth and tend to have good (i.e. little) pedal feed back characterists. Because the chain length changes little, they also tend to be easy on deraillers. They also exibit brake squat (suspension compression under braking) which stiffens up suspension (effectively pre-loading your rear shock) reducing rear wheel tracking over rough terrain while braking. Pivot location is usually optimized for a middle chain ring (for an all around bike design) or for one chainring if it's a DH design. There is usually not too much chain tension induced pedal bob, but the low pivot exhibits more CoM pedal bob than...

Forward pivot designs take advantage of better CoM coditions to reduce pedal bob (by reducing the amount the up and down motion of the human body affects pedal bob). However, forward pivot designs have substantial chain length growth and have much more pedal feedback. This is usually really noticeable while climbing technical sections in the granny ring. You can very easily get bounced right off of your pedals. They are also hard on rear derailleurs as the rear derailleur's B-tension has it's job cut out for itself compensating for the rapid change in the amount of slack chain. Because the swing arm is longer, then tend to have more lateral flex than low pivot designs.

High Pivot designs are good for DH racing because the rear wheel's initial travel is more rear ward than other designs. These bikes often feel really fast going down rough sections and almost shoot you out of the bottom of steeps. The trade off is that the chain stay length grows substantially throughout the travel, making low speed maneuvering very difficult. They are also even harder on deraillleurs than the forward pivot design. And, they require an idler pulley to align the chain with the suspension pivot. An advantage of the idler pulley though, is that it pretty much eleminates any pedal feedback, making these bikes surprisingly good climbing bikes, even though most of them have DH geometry.


Four Bar linkage designs. First off, the vertical axle path is a complete myth - no bike has it and no one would want it. It would mean big time chain stay growth that would lead to very bad chain tension "bob" as well as horrible pedal feedback.
The benefit of four bar designs are that they achieve really good pedaling characteristics with minimal chain legth growth and have the nice side advantage of being able to do some brake interaction tuning. One four bar linkage system CAN NOT be optimized to solve all three of those problems (bob, feedback, and brake interaction), but design compromises and optimizations can be made to minimize the negative aspects of each - of course tailored to a products intended application. Ie. an XC bike might almost forget about brake interaction while focusing primarily on pedal bob.
The four bar linkage does this by achieving a chain tension that is fairly perpendicular to wheel movement (low single pivot bikes are quite good at this too) to compensate for the "chain tension" component of pedal bob. However, the big advantage that four bar links have over single pivots is that they also have an "Instant Center" (read as an "effective center of rotation") that is much further ahead of the actual pivot locations. Therefor, they get the CoM advantage of forward pivot designs, with the contant chain length advantage of the low single pivot design. Throw in the ability to reduce brake squat (though not quite as much as with a dedicated floating brake, but this is a matter of perference, as some like a bit of brake squat as mentioned before) and the advantages of the suspension system are apparent.
It's disadvantages are the requirement of interupted seat tubes in long travel designs to avoid rear wheel / linkage interference with the seat / seat tube. Additionally, lateral rigidity can be compromized, but this is as much a design issue as anything. Finally, everything else being equal, multiple pivot points ALWAYS weigh more and cost more than single pivot designs.

Virtual Pivot Point (VPP) designs use chain tension to compensate for both components of pedal "bob": the chain tension component and the changing CoM component. They do this by using an "S" shaped axle path. Tension on the chain "pulls" the wheel into the "nook" of the lower curve of the "S". The chain length is the shortest there, and tension on the chain will try to pull the axle into the location of shortest chain length. The harder you mash on the pedals, the harder the chain pulls the suspension and rear wheel back into the nook of the lower curve of the "S". This design is very good at couteracting pedal induced suspension movement (bob).
The trade off here is that by using the chain length to control where the suspension is, the chain length changes drastically when moving away from the optial "nook" in the "S" shaped path. This results in substantial pedal feed back. Of course, the curvature of the axle path can be tailored to change less (hence less feedback) but that also means less pedal bob cancelling effect. Also, VPP designs can suffer from substantial brake squat, though newer designs (according to advertizing) are supposed to have reduced this somewhat. VPP designs also require a fair bit of sag to work correctly. This is great for DH oriented bikes (which typically run lots of sag), but reduces low speed maneuverability because the rider has to "pick up" more wheel travel when wanting to maneuver the rear end of the bike. Finally, VPP designs often have shock progressions that are third or fourth power curves, which mean that instead of a purely rising rate curve, you end up with a curve that may get steeper, then softer, then steeper again. This effect is subtle, but noticeable to some riders.

Parallel Linkage designs: the bad thing is that there is quite a variety of these designs now, all with substantially different ephasis on different performance characteristics. The good news is that they generally have traits that combine the advantages and disadvantages of the three types of designs listed above. For example, the Canfield Bros. design focuses on an effectively high pivot that produces a rear ward axle path to easily absorb high speed impacts.
the DW link is really not a parallel linkage design (since the links aren't really parallel) but achieves a balance of pedaling efficiency mixed in with a more plush suspension design the further you get into the travel (my limited understanding anyway, based on the www.dw-link.com website and only a quick visual analysis - I could be wrong).
I have not done any analysis on other designs like Giant's new Maestro series.

So, there you have it - a brief (kind of anyway) and certainly not complete (nor probably non-biased) look at the various technologies. Which one is best really depends upon what you want to do with it.

Let's look at DH racing: if you're racing expert or below, you probably want a frame that can compensate for some of your mistakes - four bar designs work well for this and it's no surprise that the Intense M1 was such a successful bike. However, if you're a pro-level DH racer, you generally DON'T make mistakes because any tiny mistake will cost you your race. So, other things begin to take priority: light weight and reliability probably being the top two. Since you're running only one chain ring, a single pivot location will probably be fine. You're going to be clipped in so pedal feed back won't be a huge deal (plus with one chainring only, you can minimize the amount of feedback). If they want to run a floating brake they can, but really - how much do they actually slam on the brakes? All of a sudden, a solid, simple bike makes a lot of sense - but probably ONLY to a pro-level rider.

If you're racing XC, the most important things are probably going to be pedalling efficiency and light weight. Brake interaction - who cares, XC bikes are twitchy to begin with.

If you're doing serious freeride, you most likely want a bike that's predictable, stable, easy to manuever at low speed, yet stable at high speed. It might not be as plush as a DH bike and hopefully you can get the seat up and down so that you can climb up and lower it on the way down.

That's my take anyway, FWIW and not getting tooooo complicated.

Regards,

Noel Buckley

[builttoride]

Well said Noel.

I really just want to re-emphisise that although that is the theory, and can be achieved if designed well, not all bikes out there are designed well and so are not taking advantage of the merits of the linkage design used. So don't just decide that you think one linkage is better than another cos you had a bad experience with a certain setup. Every bike is different, even ones that look the same... for example banshee and kona, they ride very differently even tho they look similar (obviously I am going to be biased here), but try them back to back and see for yourself which one you personally prefer.

So remember every bike design is different and also every rider is different, so you have to pick a bike for you, not just hear the hype and go with it. I always always encourage people to test ride bikes if they can before they buy.

[biggles604]

Originally Posted by Timmigrant

I don't agree that short-link 4-bar bikes (VPP, DW etc) exihibit higher than normal amounts of lateral flex, no different to a 4-bar anyway. However I find they can be harsher on square edged hits, and many exihibit a large degree of pedal feedback / chain growth.

On a well designed bike, the lateral stifness will be the same as any other bike, except, once the bearings start to wear, the amount of flex and play from the bearing wear will be greatly amplified, since there are 2 pivot points connecting the large lever-arm of the rear triangle. SC bikes are particularly bad, since the top two pivots are almost on top of each other. But, keep your bearings in good concition and swap them out right away, and you should have no problems.

[knollybikes.com]

Originally Posted by builttoride

Well said Noel.

I really just want to re-emphisise that although that is the theory, and can be achieved if designed well, not all bikes out there are designed well and so are not taking advantage of the merits of the linkage design used. So don't just decide that you think one linkage is better than another cos you had a bad experience with a certain setup. Every bike is different, even ones that look the same... for example banshee and kona, they ride very differently even tho they look similar (obviously I am going to be biased here), but try them back to back and see for yourself which one you personally prefer.

So remember every bike design is different and also every rider is different, so you have to pick a bike for you, not just hear the hype and go with it. I always always encourage people to test ride bikes if they can before they buy.

Thanks!

However, there are some problems with my post: I think that post is from a few years ago and there are a couple of mistakes, mainly in the four bar linkage paragraph when talking about instant centers. The rest of it is pretty much bang on.

In regards to the Sinister Passion frame: frankly (no pun intended), this is one of the coolest things I've seen in suspension development in many years. I have no idea how well it works as I've never ridden it, and while definitely not my style of bike design, the idea is pretty cool. I hope this works out well for Sinister - they are cool people and build nice bikes.

Cheers!

Noel

[ESHER SHORE]

This is funny, I tend to think it's just the opposite. Have owned FSR bikes and ridden lots of Konas, I would say FSR is very efficient when pedalling (uphills/dwonhills) and Konas were much worse climbers

I did say Banshee Faux-bar, not Kona

i've ridden Kona's Stinky and Stabs and those things had horrible "mush" under power and pedal bobbing

there is a rough visual similarity but the pivots, suspension leverage, rates, etc. are completely different

[Timmigrant]

Originally Posted by builttoride

first of all in terms of performance faux bars cannot be compaired to each other, some are far superior to others. Also a lot of it also depends on the rear shock setup.

In much the same way some single pivots are far superior to others.