Mountain Bike Reviews Forum banner

One Horst or Two? What _IS_ This??

3K views 22 replies 9 participants last post by  derby 
#1 ·
For months, I've only seen pictures of the rear triangle of this Specialized bike. I assume it's a prototype DH or FR bike but WHAT IS IT???

Anyone know why the rear is doubled and what it does?

Okay it's not really a double horst but what the heck is it?
 

Attachments

See less See more
1
#2 ·
Bikezilla said:
For months, I've only seen pictures of the rear triangle of this Specialized bike. I assume it's a prototype DH or FR bike but WHAT IS IT???

Anyone know why the rear is doubled and what it does?

Okay it's not really a double horst but what the heck is it?
That's the Demo 9 from Specialized. It is their new DH/FR/Huck bike that is actually available at dealers at this time.

Basically, it is a standard FSR 4 bar bike, but they changed the shape of the chainstay so it would push on the shock instead of the upper link.

This new design has a few of advantages:
1. It lowered the center of gravity.
2. It allowed allows the use of a 26" wheel with short chainstays.
3. Lots of new marketing hype (sells bikes).

This new design has a few disadvantages:
1. It lost it's progressive suspension linkage.
2. It got very heavy (13 - 14 lbs)
3. It got really expensive ($2800 for the frame only)
4. Lots of new marketing hype (yah, this one made both lists)

I haven't ridden one, but the ones I saw at the Interbike Demo and at the Redbull Rampage looked like they worked well, but did have very slack headangle.
 
#3 ·
Demo 9

It's the new DH bike, the Demo 9. I'm guessing that they wanted to get a long stroke shock as low as possible. It probably also lowers the leverage ratio on the shock, since the shock being activated like a single pivot, but the axle path is still a 4 bar.

Wonder if the combination of horst path/SP shock actuation has any effect on the braking forces. Brake squat maybe???

But....I'm not an engineer, and I haven't ridden it, so take it FWIW ;)

Part of it could be marketing too. After all, you did notice the funkiness and post this....
 
#6 ·
Doesn't matter what it is...

I picked one up at the LBS and later, after the hernia operation, they said my back would never be the same.

I'll hazard a guess it's close to 50lb, yes, 50! My Bullit's over 40# and this bike felt way heavier for me. Nope, the LBS was not interesting in weighing the Demo 9.

Heff...Teee.

Jim
 
#7 ·
Camouflaged Dare :)

Moving away from the previous classic Horst link design of the Big Hit, by raising the drop out pivot to the align with the axle and BB pivot geometry (although I can’t see the BB pivot), the effective suspension geometry looks like it has a very low near seat tube monopivot like path, like the Specialized XC bikes have had for a few years now. That low monopivot pedaling suspension path should work even better with platform shocks than a Horst link. Now the floating brake’s IC (the brake’s virtual pivot) is way out in front like the Dare. When braking the far forward IC will help lift the heavy rear suspension and rider up into a lighter more bump compliant spring rate above sag. Maybe Specialized is trying to avoid paying ICT licensing fees to Ellsworth/Kujima, although it may not quite so stylishly map the chain-line within the ICT requirement of 11.2% variation in a special gear set.

I don’t get why the added unsprung weight in the rear, maybe it’s easier to huck without nosedive.

Looks to me like the spring/ shock linkage with the frame is still very rising rate if not more rising rate than before.

- ray
 
#8 ·
JimC. said:
I picked one up at the LBS and later, after the hernia operation, they said my back would never be the same.
I'll hazard a guess it's close to 50lb, yes, 50! My Bullit's over 40# and this bike felt way heavier for me. Nope, the LBS was not interesting in weighing the Demo 9.
Heff...Teee.
Jim
I agree, the weight is up there, and seems mostly concentrated on the rear of the frame.

A guy who bought one posted on the old DH board that stock weight is 48lbs.
 
#10 · (Edited)
Horst link vs. ICT

Acme54321 said:
Can someone clarify the differences between ICT and Horst Link designs? they both look the same to me and I have been wondering about it for a while now.
Horst link vs. ICT is small but significant to some riders. Horst Leitner designed the 4 bar linkage to use a very low pivot near the BB, Plus a pivot near the rear dropout that was well below the axle height. This combination produced a path that was rather rearward sloping from travel top-out to sag, and curving tightly, and rather in a circular shape, to vertical with the ground a little below sag, and contiued increasing in forward slope until the path nearly faced the BB at the bottom of travel. TheHorst's virtual pivot like effect for pedaling is usually stationary, more than 2 inches behind the seat tube in a position impractical to produce with a monopivot. The chain tension effects are very significant near sag to counteract bob and squat when pedaling. And the chain tensions relaxed rapidly and digressively when compressed by bumps to remove pedal kickback stalling action and bump compliance resistance. There is no particular alignment spec for the upper link, if there is an upper link. The first Horst link bike in about 1990 was similar to and called a "Macpherson-strut" design (AMP Research B-3) followed a few years later by a "Cantilevered-Mac-Strut" adding an upper swing link with a similar angle of torque to the frame near sag. (AMP B-5)

ICT (Instant Center Tracking) typically has a higher seat tube main pivot, above the top of the small ring in height. And the drop out pivot is practically as close to the axle as possible nearly at the same height. The upper swing-link is aligned to track during travel a point the chain line and lower swing-link line cross (the IC of the floating rear link) in an average gear set used for the bike design, DH bikes aligned chain-line tracking the IC in a higher gear than XC bikes. The path is circular like most Horst links with a rather stationary virtual pivot effect nearly at the same place as the lower seat tube pivot. Compared to a classic Horst linkage, the ICT path is less rearward producing less anti-squat from top out to sag, and continues around passing equal slope with a Horst path at or a little below sag, and the wider radius ICT path has digressing chain tension similar to what a Horst does but maintaining more chain tension from effective chain-stay growth but lesser bump compliance deeper in travel than a classic Horst linkage while pedaling.

Both designs fashion the pedaling effects using a floating axle link with two swing arms from the frame. A monopivot at the same center of path radius, using the same shock rate, would act slightly different than the four-bar due to the mass inertia distributions of the links and the added friction of 4 times the number of pivots. The lighter the design the closer a four-bar with a circular path and stationary virtual pivot becomes like a monopivot would with the same pivot location. All 4-bars, whether or not they have floating axle links (using 2 chain-stay pivots) have the multiple link direction inertia and friction differences compared to monopivot swingarms. A monopivot swing arm suspension is not the same as a faux-bar seat stay, even with the exact same shock and spring rates there is a small difference. The distributed inertia of multiple swing links and slightly more pivot friction produces stabilizing effects.

With the same travel and spring/shock setup the Horst link bobs less when pedaling. ICT requires much slower damping for the same level of pedaling stability. I think Horst Leitner claimed his design to be "fully-active". Ellsworth claims the ICT to be either "100% efficient" and "up to 100% efficient", depending on which ad you look at.

Hope this helps clear up the basic differences.

- ray
 
#11 ·
Near parallelogram linkages

Bikezilla said:
For months, I've only seen pictures of the rear triangle of this Specialized bike. I assume it's a prototype DH or FR bike but WHAT IS IT???

Anyone know why the rear is doubled and what it does?

Okay it's not really a double horst but what the heck is it?
As Derby says, the suspension linkage is similar to an Ellsworth Dare. As Scott says, they've lost the progressive rising rate by using a monopivot shock linkage.

I don't know why they did the latter. They did the former because the near parallelogram linkage of the Dare works well. I made a New Year's resolution to talk less about instant centers because the concept seems to befuddle people. So here goes an attempt to explain the advantages of a near parallelogram linkage without any further reference to instant centers.

With a near parallelogram linkage the movement of the rear link where the axle is mounted is almost pure translation rather than rotation. That means that the angle the link makes with respect to the main frame changes hardly at all as the suspension moves. The link moves in a circular path but it always faces approximately the same way--like the seats on a Ferris wheel. By contrast the movement of the swingarm on a monopivot is a pure rotation around a fixed point on the main frame.

The pedaling consequence of the non-rotational movement of the rear link is that the thrusting force at the ground imparts almost no squatting torque to the main frame as it tries to accelerate the center of mass. This means almost no anti-squat is required to keep pedaling efficient--i.e. rotating the wheel rather than the suspension. In gears where the chain line is essentially parallel to the linkage, that's what you'll get--no anti-squat. By "anti-squat" I mean both extending torque--the chain tries to pull the wheel down into the ground--and kickback--upward movement of the rear wheel tries to rotate the pedals backwards.

No anti-squat means you have nothing to resist bobbing caused by the rider's weight moving around on the bike. But it also means you have no restricting by chain tension of free suspension movement when hitting bumps. And there is some lessening of weight shift caused bobbing simply from the parallelogram arrangement itself. Since there's almost no torque produced on the frame from the linear movement of the rear link, the frame resists rotating backwards in response to force pushing the rear wheel up. This causes the front suspension to compress some in response to force acting up at the rear. Whether we're talking about the rider bouncing up and down on the bike or the bike landing flat after a drop off, the upward force is distributed proportionally between front and rear. This is unlike what happens with a monopivot, or with a linkage that allows a lot of rotation of the rear link. In those cases a disproportionate share of the force is handled by the rear shock. With the load distributed more evenly between two springs and dampers, there's less overall compression.

This may be why the Dare has a reputation for being good at landing big drops and of pedaling well (although not bob-free) in spite of all the travel. It looks like Specialized is going for the same goals.
 
#12 ·
Ferris wheel chairs

Steve from JH said:
With a near parallelogram linkage the movement of the rear link where the axle is mounted is almost pure translation rather than rotation. That means that the angle the link makes with respect to the main frame changes hardly at all as the suspension moves. The link moves in a circular path but it always faces approximately the same way--like the seats on a Ferris wheel. By contrast the movement of the swingarm on a monopivot is a pure rotation around a fixed point on the main frame.
Hi Steve,
Can you elaborate how the seats on a Ferris wheel would act differently?

Of course to use the same analogy for a bike wheel the seats in both cases would be on a single axis able to spin freely, or steadied by the same force such as a chain attached to one edge of the seat. The single pivot arms hanging from giant wheel would attach to the seat's single axis, while the parallel-arm hung seat would have a floating link with the same seats rotating freely on the floating cross link on the same single axis.

I think with the 4-bar set up there would be some extra mass in the extra arms and floating link and extra friction from 4 times the number of pivots, which would slow any swinging of the seat induced from the wind across the Ferris wheel seats. But other than different mass inertia, and friction from the extra parts, how does the single arm hung seat rotate or transfer weight to the big Ferris wheel any differently?

Without the seat's free spinning axis on the floating link or lower end of the single swinging arms, and the seat were attached directly to the hanging single swing arms, or attached to the floating link across the double-swingarms, you have the same situations as during braking a monopivot braked wheel compared to a floating braked wheel. There are significant differences in that case.

Please critique where I may have skipped any facts.

Thanks in advance for the clarification.

- ray
 
#13 ·
The seats on the ferris wheel were only meant to illustrate the type of motion called curvilinear translation. With respect to the frame of the bike the floating link of a parallelogram linkage moves that way. Again with respect to the frame of the bike the swingarm does not move that way.
 
#14 ·
Steve from JH said:
The seats on the ferris wheel were only meant to illustrate the type of motion called curvilinear translation. With respect to the frame of the bike the floating link of a parallelogram linkage moves that way. Again with respect to the frame of the bike the swingarm does not move that way.
Thanks again. I sounded as if you were implying that there would be different wheel and frame effects when pedaling with the same path from the BB when using either one or many swing links between the frame and the axle. Which of course there aren't, apart from pivot friction and link inertia effect differences (at least not in a causal universe!).

Although the inertia and friction differences can be significant enough to smooth pedaling effects using widely distributed multi-links compared to the more concentrated mass with less friction thus quicker reacting single swing linkage, even though the effective path geometry balance was the same in both applications.

An abstract example would be applying the same launching effort to 2 same sized wheels, one with a heavy tire and one with a very light weight tire. The light tired wheel would quickly accelerate and roll into a bumpy section and it would bounce high and off line and come to rest quicker than the heavy wheel. The heavy tired wheel would accelerate more slowly and roll slower with the same launch energy input, but the directional momentum would be maintained much longer with less bounce and deflection, perhaps to far out distance the lighter wheel in the launch direction in the same rough terrain. Now if the tires were the same weight but the hub weights were very different, there would not be much difference in bounce and deflection direction or distance in journey. The wheel with the heavier hub would do it at a slower speed from the same launch input.

However, locking the wheel with friction (or othe means of attachment or drag) to a floating link vs. to a single swing link with the frame (on of a mult-swing-arm design or single swing-arm), usually has very different effects with the frame.

- ray
 
#15 ·
derby said:
It sounded as if you were implying that there would be different wheel and frame effects when pedaling with the same path from the BB when using either one or many swing links between the frame and the axle
Of course that's exactly what I'm saying. Once again, and I know you know I believe this, the wheel and the link to which it is attached have to be thought of as acting like a single rigid body as far as force from the ground is concerned. Ground force produces a reaction at the frame pivot, not at the axle.
 
#16 ·
True, if the wheel is locked to the link it's axle is on, such as during braking or catching a stick in the spokes. I usually try to have no brake rub when pedaling so my rear wheel rolls freely. I'm slow enough already!

Without a stick in the spokes or brake friction, how can you imagine the wheel's swing or floating link is attached (except when braking)? After a few years studying this subject, that's never been demonstrated to me. I do see the chain attached to the frame (when rider is seated and pulling on the bars , so wedged into the frame, resisting/locking pedal backspin) and chain attached to wheel (cog), wheel attached to ground. So there is a correlated relation of the ground to the frame (when rider is seated) through the wheel. But the wheel is only the leverage activator, pressuring the linkage only through the axle (unless using the brake). And the linkage can rotate about the axle directed by the path with the frame. Why not?

- ray
 
#17 ·
Derby and Steve make my brain hurt...

Kidding, appreciate the knowledge and interest in all things FS.

I've sat on, but not ridden, a Demo at my LBS here in Minnestrohta. First, it's a porker 48#+ for a medium. Cool to see all that tech go into the frame - more so on the front triangle (esp HT) vs. the rear end. Also, for a medium, it seemed long in the TT relative to other big hit/DH bike I've saddled. I've not compared actual specs.

It's clear Speshy invested a lot of time and $ on this bike. Won't even touch the tech differences or +/-'s in designs other than they seemed to manipulate a ton of stuff without it being entirely clear as to why. Can't an M-1 or M-3 clear a 26" wheel and still use a more "traditional" FSR style rear end vs. the monopivot shock actuation? Hasn't Intense also done that pretty effectively?

Now, as a non-DH/hucker I cringe when looking at the bolt on front and rear wheels - front 6(?) bolts and rear 8(?) bolts to change a flat? Yikes. Then again, you probably don't flat the big meats as often...or maybe you do. Thankfully the bike should work with a host of aftermarket shocks vs. the Epic/FSR/Enduro designs which receive one-off Speshy-particular pieces from Fox (ITCH, etc.).

Unfortunately, you can't even justify the complete big box spec based on cost as, for the dough, I'd buy something else - DHR, M1, Fly, etc. - that was proven. The one at my LBS was $4800. Shoot, you can get a race-spec SGS for way less than that at equal to better parts spec.

Sean
 
#18 ·
If only you understood this fundamental point--that the force from the ground that drives the bike across the ground produces a reaction at the suspension pivot, not at the axle, everything would fall into place. Without this fundamental assumption the pole of moments theory that you've been using makes no sense. You can't explain why your own bike performs as well as it does. Nor why Dave Turner evolved his design in the direction he did. And why other makers, such as Devinci, Azonic, Craftsman, and now Specialized have done similarly.
 
#19 ·
Sure the ground produces a reaction at the monopivot or effective virtual pivot for multi-links, but only in the direction of it's path around the axle. For consistent comparison between various systems, multi-link to multi-link, single-link to multi link and single to single, the virtual pivot's path around the axle is the exact inverse of the axle path around the virtual pivot. That is done for consistent comparisons, without exceptions or class exclusivity. However if tensions mapped at a floating axle linkage’s virtual point IC is to be compared with a single swing linkage, then the virtual IC of the single link of infinity should be measured for consistency between all systems. Path (a map of linkage slope) is consistent and common with both measurement methods.

So maybe there is a semantics problem, an x/y perspective difference. Hold the axle still as the x/y perspective, and rotate the frame (while remaining stable at the same pitch), and every point of the frame (including the virtual or physical pivot) will trace the same path in inverse direction as the axle would when the frame was held still as the x/y perspective. It's easier to show the axle drawing the map of the path, the inverse action to the frame is assumed to be obvious, I guess, in common bike suspension conversation. Perhaps I should talk in terms of the frame path around the axle. They both, the axle and (virtual) pivot, have uniquely unbalanced tensions when the chain is wrapped around the wheel or cog is tightened from the frame. And the equal and inverse tensions at the axle then occur at the (virtual) pivot if the axle cannot move in the same direction of it's tension, whether the axle is prevented from being driven towards the ground because the wheel rolls in the way, or held down from lifting by gravity and/or enough extending tension.

Of course if there is a floating axle link then the from path is guided by 3 more links, and rotate the stable frame path about the axle consistent and inverse with the path of the axle around the frame's virtual pivot when frame is kept from moving. It's a more complex set of paths to obtain the same axle to frame relation.

There is some loss of purely path geometry effect due to mass and friction differences between various systems including different monopivot structures and weights. Add into the non geometry mix the varied damping and spring rates, and the geometry effects become quite muddied, like the difference between riding dry hard-pack and sticky mud. The magic of physics is that it is consistent, unlike hearsay.

Turner told me why he moved away from a classic Horst design. So the rear derailiur wouldn't bag against the low hung pivot nearby. At the same time he raised the BB pivot about the same amount to keep about the same path and resulting anti-squat bob reduction near sag. At least that what he told me. And Dave is too personable to be hyping that. He chuckles at the mention of ICT. He uses feedback from pro riders on other design tweaks.

I don't know why the others did. Specialized followed soon after Turner and moved the BB pivot up slightly and an inch more rearward to try to compensate in path platform. But they couldn't move it far enough back to save the earlier snappier more platform geometry pedaling effect. And like ICT, Specialized lucked into a better path for letting tunable platform shocks take over the pedaling efficiency effects more completely.

- ray
 
#20 ·
I can't follow most of this. But you seem to be saying that if a linkage bike and a single pivot bike have the same axle path then they have the same axle path. Of course it doesn't matter whether you fix the frame and move the axle or vice versa; it's still the same.

This is all irrelevant since I am not talking about axle path.

The point at issue is whether we can consider the wheel and the link to which it is attached as acting like a single unit as far as the torque produced by the thrusting force at the ground is concerned. If so then axle path is irrelevant as regards this particular torque. This assumption is made in all of the suspension theory I have read about formula race cars, drag racing, and motorcycles. As I said this assumption lies behind the pole of moments theory or instant center of forces theory used by motorcycle theorists.

An analogy can be made with what happens with the reactive chain force pulling back on the chain ring. In KS's Path Analysis he concludes that Ola was right in saying we can think of this force as acting backward on the frame along the line of the chain. This would then induce a parallel force acting backward at the frame pivot point not at the bottom bracket. Likewise the reactive force at the ground induces a parallel force at the linkage or swingarm pivot point not at the axle.

To describe all this without talking about instant centers or pivot points--the task I set myself--we have to look at the difference in the pattern of movement of the wheel/link unit in each case. Attached (I hope) you'll see diagrams derived from the ID in Linkage. In #1 I have erased all the links but the floating one and shown it juxtaposed in two positions--full extension and 75mm travel. In #2 I have done the same but erased all the links but the lower swingarm. (We can pretend that the axle is on that lower swingarm since it is so close).

In #1 you'll see that the movement is more vertical translation with only slight rotation. In #2 the movement is entirely rotation. The thrusting force will produce more torque on the frame in #2 in proportion to the angular difference. Bump forces will do the same thing, producing some compression of the front from rear compression in #1 but not in #2.
 

Attachments

#21 ·
Well the ID or any ICT labeled bike is not a good example of a floating axle link since the dropout pivot is so close to the axle it is virtually concentric and monopivot like in pedaling tension geometry. Nearly no pedaling induced chain and cog tension, pulling at the axle, is distributed to the upper link into the frame up high. And the pivot could be on the other side of the axle and have nearly the same pedaling and bump compliance effect. ICT does have a floating brake unless the brakes were attached somehow to the lower link. Unless there is some magic in the ID, virtually all the rear suspension bump input activation that influence the front suspension is due to rear shock resistance.

With the ICT bikes like monopivots, the pedaling effects are as you said just above, conditioned virtually entirely by the lower link to frame alignment action. I'd add to that the chain-line and BB height. I think I'm in agreement with you there.

I'm curious if the Rocky ETX 4-bar design is close to ICT in some gear set. That bike has a extreme floating axle.

- ray
 
#22 ·
The Id is as much an example of a floating link as any other. There are no degrees of gradation here. Either the axle is separated by two pivots at top and bottom from the frame or it is not.

Once again you're just arguing based on the faith that axle path alone explains everything. I'm showing how that is not true. The wheel drives the link to which it is attached. The link moves differently if it is a floating link. That difference imparts a different reaction at the frame and even on to the front suspension.
 
#23 ·
Well I think I have more of a kinematics perspective than a black and white fundamental notion of floating axles.

Here's simple abstract of the difference in various floating links: If you take a 10 foot see-saw with a fulcrum exactly in the middle and balance it with the weight of one sandbag on either side, the sandbag weights would be equal. If the fulcrum was moved toward one end of the see-saw, the shorter side of the see-saw will require a greater proportion of the total amount of sand in both bags. If you move the fulcrum to be just 6 inches from one end of the see-saw all the weight of both sand bags may not be even enough to balance the cantilevered weight of the see-saw board itself.

The fundamental bench rocking experiment of ICT theory omits the use of a floating axle link. A seesaw with a fulcrum needs to be placed under the bench's legs to simulate the general effects of a floating axle. Move the fulcrum near one end, and note that the bench then collapses if the person is not re-centered over the fulcrum (or even further past the re-centered point to support the unbalanced weight of the cantilevered seesaw and bench and leg).

Hope this makes the point of the importance of the location of the axle on a floating link more clear. The effect of the axle cannot be ignored in floating axles or monopivoting axles

- ray
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top