Suspension: What ever happened to "falling rate" designs?

[BRacing]

Mtb suspension has been going largely to a "rising rate" design using a coil spring + air spring. This ramps up the total spring rate at the end to prevent harsh bottoming.

But a few years back (maybe a few more? I'm gettin old...) all the suspension talk was rising rate vs. falling rate vs. linear rate by manipulating different suspension designs.

My question is, are there any more successful "falling rate" designs out there?

What are/ were the most popular "falling rate" suspension frames?

Discuss...

-Brad

[binary visions]

Generally, any frame with just one pivot (i.e. no linkage) is a falling rate design, and there are lots of them. The Orange frame is winning lots of pro races, and the Bullit is one of the most popular freeride frames available.

As to how this relates to your first two sentences, I'm not sure. A lot of companies are sticking with a very simple frame design and using the shock to create the necessary progression. That doesn't mean that there aren't still progressive linkage designs out there, though, and plenty of them. The Yeti AS-X is very similar to a Bullit in design and target market, but it uses a linkage to create a progressive design. Most four bar designs are progressive to some extent such as the Kona Stinky series.

The upshot is, I think there's a lot of both designs on the market - and that's great for the consumers. More choices is always better!

[BRacing]

Hmmm, I was under the impression that a single pivot (ie Bullit) suspension design is a straight rate.

-B

[binary visions]

Hmmm, I was under the impression that a single pivot (ie Bullit) suspension design is a straight rate.

-B
Oops, I meant to include "straight" in there (straight or falling rate), but I believe most of them are, actually, falling rate designs - just most of 'em don't fall much.

[RhinofromWA]

I don't know Suspension from a hole in the wall :D but I thought single pivot linkless systems can have a rate that is rising....:think

For sh!ts and giggles I will use and abstract example for a demonstration. :rolleyes: :)

A cars motor....more specifically a crank, rod and piston of the engine. At the dead bottom of the crank the piston pauses, right? as it rises to a 90 degree point it is accelerating from a dead stop....I am pretty sure. As it passes the 90 degree point it is slowing down until it reaches the top if the crank and stops at it's highest point. The first 1/4 of the travel is accelerating and the 2nd 1/4 is slowing down....wich is then repeated in similiar fashion as the piston returns to bottom center.

I know this may be messy but if you take the center of the crank as the suspension pivot and the lower rod and piston as two mounting points of the shock. Than if a shock was operating in the first 90 degrees of motion, it would be a rising rate, right? :confused: *shrug*

The next question is "Is it enough to notice?" :rolleyes: :D

[RhinofromWA]

Much like early motocrossers found that laying their shocks down instead of sticking they straight up (perpendicular to the swing arm) gave a better ride......for the most part.

OK I am done talking moto stuff in relation to MTB...:o: you probably didn't w2ant to hear my babbling anyway. :)

[ChrisRobin]

I thought a Bullit was falling rate, not straight rate. With a 5th Element, by cranking up your air volume or whatever keeps the shock from bottoming out harshly you end up with a more linear suspension rate.

[binary visions]

I'm a little too addled from my rediculous day at work to give a good description of the picture I have in my head, but suffice to say you really need a linkage in order to make a suspension rate progressive - at least, from all of my knowledge.

Single pivot, no linkage bikes are all falling rate but some of them are close to linear - less so as you increase the amount of travel.

Let me see if I can find a good description as to why when I get home tonight. Or take the time to put what's in my head down on paper (see, disadvatages of learning through talk rather than through textbooks - I don't have good explanations for certain pieces of my knowledge :D )

edit: ChrisRobin, you posted before I got this all typed - yes, you're correct, the Bullit is a falling rate design just like all non-linkage single pivots.

[El Caballo]

On a single pivot bike, one end of the shock is moving in a circle and the other end is fixed. Therefore the rate can be rising or falling depending on what part of the circular "stroke" the shock occupies during normal suspension travel.

It's easy to figure out which: draw two lines from the shock eyelet on the swingarm, one through the shock eyelet on the frame, and one through the swingarm pivot. The shock has a rising rate when the angle between these lines is moving towards 90 degrees (decreasing from a larger angle, or increasing from a smaller angle), and a falling rate when the angle is moving away from 90 degrees.

From eyeballing pictures, it looks like a Heckler is always falling rate. A Bullit looks like rising rate at the beginning of the travel and falling rate for the rest. A Joker looks like falling rate.

It would be tough to mount a shock in a place where the angle could stay above 90 degrees for the entire suspension travel. Motorcycles do it, but they have more room because of wide tires and no cranks.

[w00dy]

You can do any kind of rate with or without a linkage, it's just a matter of shock placement. For the most part falling rates are not used on bikes made to take big hits because they bottom out more harshly than rising rate ones. There's still a few out there that I know are falling rate. The Rocky Mountain slayer is one example.

[mack]

i think some people are getting the 'rates' confused with axle paths...

A 4 bar is a rising rate but has a straight axle path (ex. FSR) Vpp is somthing different altogether.

[Toshi]

A cars motor....more specifically a crank, rod and piston of the engine. At the dead bottom of the crank the piston pauses, right? as it rises to a 90 degree point it is accelerating from a dead stop....I am pretty sure. As it passes the 90 degree point it is slowing down until it reaches the top if the crank and stops at it's highest point. The first 1/4 of the travel is accelerating and the 2nd 1/4 is slowing down....wich is then repeated in similiar fashion as the piston returns to bottom center.
On a single pivot bike, one end of the shock is moving in a circle and the other end is fixed. Therefore the rate can be rising or falling depending on what part of the circular "stroke" the shock occupies during normal suspension travel.
:oink: yup, it is possible to have a rising rate with a single pivot, and rhino's example of the early mx guys having their shocks "laid down" instead of straight up shows how it is accomplished.

[binary visions]

A 4 bar is a rising rate but has a straight axle path (ex. FSR) Vpp is somthing different altogether.

No no no no nononononononononono. ARGH.

A 4 bar is NOT necessarily a rising rate, and does NOT EVER have a straight axle path, FSR or not.

[binary visions]

yup, it is possible to have a rising rate with a single pivot, and rhino's example of the early mx guys having their shocks "laid down" instead of straight up shows how it is accomplished.

Doesn't this still have a small linkage, though, a'la Rocky Mountain RM# series or the Turner DHR? Isn't that the only way to accompish the proper actuation of the shock when it's laid down flat like that?

I guess my statement was a little too "blanket", but I was indicating single pivots like a Bullit/Heckler/Gemini/Prophet/Jeckyll/etc.

[Kornphlake]

generic explanation for rising rate or falling rate or linear would be if the instantaneous leverage ratio is rising, falling or constant. A bullit is falling rate (I guess, I don't have a schematic in front of me) because as the suspension compresses the shock moves from an angle where the force vector (which in the case of a bullit is a tangent to a circle concentric with the main pivot) is more parallel to the shock to an angle where it is less parallel to the shock, as the suspension compresses further the angle becomes farther from parallel.

[RhinofromWA]

A 4 bar .....does NOT EVER have a straight axle path, FSR or not.Thank you for looking past the maketing :)

I have always told people that a FSR type of 4-bar "can" create a shallower arc, or a more vertical axle path but it is not straight.

[binary visions]

I have always told people that a FSR type of 4-bar "can" create a shallower arc, or a more vertical axle path but it is not straight.
According to those with more experience than I, most FSR 4-bars actually create a wider arc than most single pivots... See "? for DW" in the Downhill forum.

[mack]

some one needs to make a chart or graph to clear this up! i am so confused, i was certain 4 bar desing had a straight axle path. :confused:

[El Caballo]

A Horst link is basically a single pivot with a floating brake and an adjustable shock leverage/rate curve.

Visualize it: the second pivot is very close to the rear axle, and doesn't move over any more of an angle than the swingarm does. It doesn't meaningfully affect the rear axle path.

There's nothing wrong with this, it's a good design, and there's a reason lots of people put floating brakes on single-pivot DH bikes. I personally think the arguing over rear axle path is somewhat overblown.

[caputo1989]

they aqll seem to work pretty well

[The Kadvang]

some one needs to make a chart or graph to clear this up! i am so confused, i was certain 4 bar desing had a straight axle path. :confused:

Just think about it. Take your arm and hold it straight out infront of you. Swing it 90 degrees to the left or right. Think of the path your hand took, it is curved, with your arm (or one bar of the suspension) being a radi in the curve of the axel path. Four bar does not mean FSR. Konas are four bar but they have the axel path of a single pivot.

[RhinofromWA]

According to those with more experience than I, most FSR 4-bars actually create a wider arc than most single pivots... See "? for DW" in the Downhill forum.That is what I meant by "shallower".....less curve, but not straight. THe marketing guys call it straight. The same marketing guys probably brag they have 12" wangs....but come on....they can't all be hung like me :rolleyes: :) j/k

I thought the ? dor DW thread was about how to get into the industry and what schooling to take......not axle paths.....I think I will stay away from that thread.

[binary visions]

That is what I meant by "shallower".....less curve, but not straight. THe marketing guys call it straight. The same marketing guys probably brag they have 12" wangs....but come on....they can't all be hung like me :rolleyes: :) j/k

Actually.. I didn't mean a wider arc.. I actually meant a deeper arc - more curve.

...and don't make me whip it out and show you what I bring to the party...

[towelie]

Yeah- what Kornphlake said.

On a picture of a single pivot bike, take a compass and draw a circle centered on the main pivot, with your circle going through wherever the shock mounts on the swingarm. Now, at random points along that circle, you can draw lines from your arc to where your shock mounts to the frame.

If these lines become MORE tangential to the arc as the swingarm progresses through it's travel, the shock can push on the arc harder and you have a rising rate.

If these lines become LESS tangential to the arc (ala Heckler), the shock can push on the arc with progressively less force, and you have a falling rate.

If these lines are tangential in the middle of your travel, but less so at the ends, you have an approximation of a linear rate, but you can't have a TRUE linear rate on a single pivot bike. (It sounds like the Bullit may fit into this catagory)

[mack]

so what the hell is VPP?

[towelie]

Depends where you put the shock, but my Blur appears to be roughly linear. It looks like it starts out slightly rising rate, is linear in the middle, and maybe slightly falling rate at the end.

Falling rate only really has one advantage that I can think of: When used with an air shock, it helps counteract the rising spring rate such shocks get as they compress. Of course, this is less of an issue with modern, "high volume" air shocks.

[binary visions]

so what the hell is VPP?
Did you mean, what suspension rate is VPP, or what kind of axle path do you get from it?

[El Caballo]

VPP is very similar to dw-link. Instead of having a pivot located near the rear axle, the rear triangle is rigid, and is connected to the frame by two link bars.

On the VPP they rotate in opposite directions, on dw-link they rotate the same direction. This will primarily affect the way they brake, because the rear triangle is rotating forwards on a VPP and not rotating much at all on a dw-link.

I will guess that a VPP will feel more like a single pivot under braking and a dw-link will feel more like a Horst link -- but this is a guess.

The ETS-X and Canfield Bros frames are similar to the dw-link, but they have longer link bars and different shock linkages.

[binary visions]

VPP is very similar to dw-link. Instead of having a pivot located near the rear axle, the rear triangle is rigid, and is connected to the frame by two link bars.
<snip>
The ETS-X and Canfield Bros frames are similar to the dw-link, but they have longer link bars and different shock linkages.

Only visually and in the physical structure of the suspension system (i.e. two linkages connecting solid rear triangles) are any of those frames similar.

Pedalling, axle path, braking, etc. will all be very different.

You may know that but most people don't and your post is likely to give people the wrong impression :)

[El Caballo]

Pedalling, axle path, braking, etc. will all be very different.

You may know that but most people don't and your post is likely to give people the wrong impression :)

You're probably right. Variation within a design has huge effects, often more than changing designs.

The variation in single-pivot frames alone is amazing, depending on where you put the pivot, what sort of shock linkage you run, and your frame geometry.

[ALEXIS_DH]

Generally, any frame with just one pivot (i.e. no linkage) is a falling rate design, and there are lots of them. The Orange frame is winning lots of pro races, and the Bullit is one of the most popular freeride frames available.

As to how this relates to your first two sentences, I'm not sure. A lot of companies are sticking with a very simple frame design and using the shock to create the necessary progression. That doesn't mean that there aren't still progressive linkage designs out there, though, and plenty of them. The Yeti AS-X is very similar to a Bullit in design and target market, but it uses a linkage to create a progressive design. Most four bar designs are progressive to some extent such as the Kona Stinky series.

The upshot is, I think there's a lot of both designs on the market - and that's great for the consumers. More choices is always better!



WTF??? a single pivot being anything other than linear??

there are 2 kinds. linear and non-linear rates. non-linears can be falling or rising.

single pivots have linear rates.

if anyone wants to argue on that, i´ll post the math later. but that was the first thing i was taught in engineering dynamics.

[BRacing]

Technically, most everything is non-linear (including single pivot). If the first thing your class is teaching is advanced suspension design, then you're probably in the wrong class.

-B

[ALEXIS_DH]

Technically, most everything is non-linear (including single pivot). If the first thing your class is teaching is advanced suspension design, then you're probably in the wrong class.

-B


c´mon, dont go to technicalities, thats for phylosophers and Phd. scientists. or we´ll go into the imperfect friction coefficient in the damper, thus making this linear vs non-linear argument irrelevant.

am talking about the broad engineering concept on linear system and non-linear. my class was statics or dynamics, i dont remember, but it was a sophomoric class.

i dont have the math at hand, and am to lazy to figure it out, but the relation in a single pivot between the shock lenght and the delta of position in the wheel is a matter of sines and cosines of the delta-angle of the swingarm, instead of an exponential (non-linear) relationship.

[El Caballo]

WTF??? a single pivot being anything other than linear??

there are 2 kinds. linear and non-linear rates. non-linears can be falling or rising.

single pivots have linear rates.

if anyone wants to argue on that, i´ll post the math later. but that was the first thing i was taught in engineering dynamics.

Sine and cosine are nonlinear functions. Therefore, no single-pivot frame can have linear rate without a compensating shock linkage.

Also, non-linear functions can be falling in some places and rising at others -- for example, sine and cosine.

I hate to say this, but either your dynamics professor is ignorant or you aren't retaining information well. This is basic math.

[binary visions]

Alexis, please post this math and don't cheese out with the explanation that you're "too lazy to figure it out".

You have several people telling you that you're wrong, and you've just said, "No, you guys are wrong, but I'm too lazy to tell you why."

c´mon, dont go to technicalities, thats for phylosophers and Phd. scientists.
:rolleyes:
For short travel bikes, the rate can be almost linear, simply because of the very short shock stroke.

When you get into longer travel bikes, though (4+ inches), the falling rate is certainly not a "technicality" - it's very apparent and affects the way the bike rides. That's no small reason why the 5th Element made the Bullit such a wildly successful bike: sure, they were selling them with Fox RCs, but putting on a progressive shock (pedalling platform aside) made the bike a completely different creature.

[RhinofromWA]

Could a bike using a sliding track like the new Yeti DH bike and a good shock location make that design linear...even if it is not desireable. ;)

A slotted rear suspension travel; sliding in direction with teh shock would be a linear design.....

:confused: right? :D

MOst other designs require the qualifiers (ie. almost, yadayada-like, close to, etc) to even try and claim a linear path technically. THought the degree at wich the rate changes might be so small for all practical purposes you couldn't tell it wasn't linear.

Tweet! (2 minute penalty for Rhino's incoherant babbling)

[binary visions]

A slotted rear suspension travel; sliding in direction with teh shock would be a linear design.....
Well, that would give you a perfectly verticle suspension path, which is terrible from a rideability perspective, but yeah, it'd give you a linear design. Of course, it'd also give you a 1:1 leverage ratio so you'd get very little travel out of a very large shock :D

At least, if you're describing what I think you are. You mean, if the swingarm slides upward, compressing a shock that is mounted parallel to the seat tube, right?

You need to have a pivot point of some kind (even if it's imaginary) to achieve a leverage ratio, though, so I don't think you could ever have a perfectly linear rate.

It would seem to me to be relatively easy to design an approximately linear rate through a linkage, though, since the stroke of ANY bike shock is at most 3.5".

edit: Upon further reflection, the axle path wouldn't necessarily have to be vertical for your proposed scenario, but it would be straight (i.e. no arc), which again is bad from a usability perspective, and you still have the leverage ratio problem.

[RhinofromWA]

Well, that would give you a perfectly verticle suspension path, which is terrible from a rideability perspective, but yeah, it'd give you a linear design. Of course, it'd also give you a 1:1 leverage ratio so you'd get very little travel out of a very large shock :D

At least, if you're describing what I think you are. You mean, if the swingarm slides upward, compressing a shock that is mounted parallel to the seat tube, right?

You need to have a pivot point of some kind (even if it's imaginary) to achieve a leverage ratio, though, so I don't think you could ever have a perfectly linear rate.

It would seem to me to be relatively easy to design an approximately linear rate through a linkage, though, since the stroke of ANY bike shock is at most 3.5".

edit: Upon further reflection, the axle path wouldn't necessarily have to be vertical for your proposed scenario, but it would be straight (i.e. no arc), which again is bad from a usability perspective, and you still have the leverage ratio problem.I thought we were E-babbling about linear rate designs? :D

Screw if it would actually be a joy to ride. :sneaky:

I was describing a true linear design......period. As with much of this discussion, the fact you can or can't tell the difference or if the design can be truely created is irrelavent. No one cares here. :)

[binary visions]

I was describing a true linear design......period. As with much of this discussion, the fact you can or can't tell the difference or if the design can be truely created is irrelavent. No one cares here. :)
No doubt.. I wasn't criticizing your post, just thinking out loud about the disadvantages of the design. :D

[flymybike]

A shock mounted straight in line with a straight axle path is the only I know of to acheive a truely linear rate. When you introduce a arc, whether it is a axle path arc or shock engagement rotation you will get a non linear rate. You could make it close to linear but not truely through the entire range of travel.
As for a single pivot, as you lay the shock over you get a more progressive rate. If the shock starts at 90 degrees to the compressive member and swings away from 90 you get a regressive design.
There you go.

[Spunger]

I am pretty sure my Cortina Joyride is a falling rate. Probably why the dumb thing bottoms out constantly :)

I know the stable platform shocks help bandaid the falling rate suspensions. I thought about it for a while but figured we'd just keep the Float RL and use it till it busts.

[thaflyinfatman]

i dont have the math at hand, and am to lazy to figure it out, but the relation in a single pivot between the shock lenght and the delta of position in the wheel is a matter of sines and cosines of the delta-angle of the swingarm, instead of an exponential (non-linear) relationship.

Uh, you are aware that sinusoidal (and similar) relationships aren't linear functions.... hence why they're called "circular" functions.... right?

No bikes are truly "linear", but some singlepivots are close to the point where I don't think a person would be able to tell the difference.

What makes a significant change in rate (ie to make it noticeably rising-rate or falling rate) is when the angles of the suspension members (esp. relative to the shock's axis) change quickly. Shorter links = greater opportunity for rate change. You can set up a single pivot to be mildy rising-rate, but you can't do it as much as you can with a linkage design because the swingarm has to be at least the length of the wheel's radius + a bit; with a linkage you can make the links waaaay shorter than that and get a much greater change in the angles. [/basic explanation]

[binary visions]

Uh, you are aware that sinusoidal (and similar) relationships aren't linear functions.... hence why they're called "circular" functions.... right?
I'm not sure I've ever heard a logical argument out of Alexis.. Anyone remember that wild thread about Dorados and how he would type pages of pages of arguements that said, basically:

A) Nobody was a "real" DH racer if you weren't a South American, flying-all-over-the-world, world-cup-winning racer, and

B) Because his friends didn't have Dorados, they were unreliable, high maintenance, terrible forks.

[BRacing]

Remember guys, this is a technical discussion. You all have brought some interesting points to the table so far, so keep the 'name calling' out of it.

FlyinFatman: A very good explanation thus far.

I wish we had a list of popular bicycles, and could list them as rising, linear (or close to it), or falling.

-B

[binary visions]

Remember guys, this is a technical discussion. You all have brought some interesting points to the table so far, so keep the 'name calling' out of it.
Okay mom ;)

There was no name calling; sometimes it is wise to point out when you are arguing with someone who will not answer to or be swayed by logic. It avoids what I mentioned had happened before in my post: pages of illogical and inane argument.

We now return you to your regularly scheduled program...

[Spitfired]

The best description I can give for a single pivot:

Visualize a single pivot. If you draw a line from pivot to shockmount(swingarm) and then to shockmount(frame) and measure the angle between those at full extension and full compression you can get a good idea of rising for falling. If the extended angle is less than 90 and the compressed angle is less than or equal to 90, you've got rising rate. If it's initially greater than 90, chances are under compression that angle will go up (heckler for example).

For rising rate, the shock's mechanical advantage at the 90 degree is higher than that of the fully extended less than 90 degree angle. At full compression, it's pushing sraight against the swingarm - all of the springs force is concentrated in that line. As the swingarm goes back towards full exension, and the angle gets smaller, the shocks pusing force is going to be less on the swingarm.

Likewise, on a falling rate, as you compress he swingarm hat angle gets even larger than 90 making the mecanical advantage go down throughout the travel.

Heres a picture of a rising rate SP I made for you right quick

[FlipSide]

Good explanation Spitfired...I was about to post something similar! :thumb:

[thaflyinfatman]

I'm not sure I've ever heard a logical argument out of Alexis.. Anyone remember that wild thread about Dorados and how he would type pages of pages of arguements that said, basically:

A) Nobody was a "real" DH racer if you weren't a South American, flying-all-over-the-world, world-cup-winning racer, and

B) Because his friends didn't have Dorados, they were unreliable, high maintenance, terrible forks.

ahaha, did you see the 24/26 debate? He was pro-24" because it accelerates faster and you're "always accelerating" (in response to me saying "you're not always accelerating" taking "acceleration" to mean positive and "deceleration" to mean negative)... never mind that you'll average a lower speed with the greater rate of positive AND negative acceleration. But that's just what you want for dh racing!

[Gravity Ho]

Anybody else getting a nose bleed from reading all this? And here I thought I was a geek! :p

[zane]

The best description I can give for a single pivot:

Visualize a single pivot. If you draw a line from pivot to shockmount(swingarm) and then to shockmount(frame) and measure the angle between those at full extension and full compression you can get a good idea of rising for falling. If the extended angle is less than 90 and the compressed angle is less than or equal to 90, you've got rising rate. If it's initially greater than 90, chances are under compression that angle will go up (heckler for example).

For rising rate, the shock's mechanical advantage at the 90 degree is higher than that of the fully extended less than 90 degree angle. At full compression, it's pushing sraight against the swingarm - all of the springs force is concentrated in that line. As the swingarm goes back towards full exension, and the angle gets smaller, the shocks pusing force is going to be less on the swingarm.

Likewise, on a falling rate, as you compress he swingarm hat angle gets even larger than 90 making the mecanical advantage go down throughout the travel.

Heres a picture of a rising rate SP I made for you right quick

This was practically what I was planning to say.

[towelie]

Hmmm...I was just thinking about something that may through a wrench into the works here.

While my statement a few pages back says essentially the same thing spitfire just said, I think we may be neglecting something important. That is, the further the swingarm gets from horizontal (horizontal line from the pivot to axle), the more degrees of rotation are needed to get a vertical inch of travel. In an extreme case, if the swingarm went totally vertical you'd get practically no travel for large swingarm rotations. Because of this, a higher pivot location may give more of an effective rising rate, and a lower pivot location may give more of an effective falling rate, even if shock locations are the same. This is because in the higher pivot location, the swingarm is becoming more perpendicular to the direction of desired wheel travel (up). Of course, the higher the pivot, the shorter the bar between the pivot and shock mount, and the tighter the arc the shock mount follows. Tighter arcs will always keep it from being more linear, so maybe inches of travel per degree of pivot motion are in the wash here. Still, something to think about.

[zane]

Yeah, that's true. I was thinking about this the other day when I was modeling suspensions. You'd have to take the rate by the swingarm into account when calculating overall rate.....

You'd basically have to graph all of the rates of each link (the more links the more separate rates you'd have) and take the superposition of all the graphs to get the overall suspension rate. This is the most accurate way I can think of to calculate the final overall rate.